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// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'dart:math' as math;
import 'dart:ui' as ui show Image, ImageFilter, TextHeightBehavior;
import 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'binding.dart';
import 'debug.dart';
import 'framework.dart';
import 'localizations.dart';
import 'widget_span.dart';
export 'package:flutter/animation.dart';
export 'package:flutter/foundation.dart' show
ChangeNotifier,
FlutterErrorDetails,
Listenable,
TargetPlatform,
ValueNotifier;
export 'package:flutter/painting.dart';
export 'package:flutter/rendering.dart' show
AlignmentGeometryTween,
AlignmentTween,
Axis,
BoxConstraints,
BoxConstraintsTransform,
CrossAxisAlignment,
CustomClipper,
CustomPainter,
CustomPainterSemantics,
DecorationPosition,
FlexFit,
FlowDelegate,
FlowPaintingContext,
FractionalOffsetTween,
HitTestBehavior,
LayerLink,
MainAxisAlignment,
MainAxisSize,
MouseCursor,
MultiChildLayoutDelegate,
PaintingContext,
PointerCancelEvent,
PointerCancelEventListener,
PointerDownEvent,
PointerDownEventListener,
PointerEvent,
PointerMoveEvent,
PointerMoveEventListener,
PointerUpEvent,
PointerUpEventListener,
RelativeRect,
SemanticsBuilderCallback,
ShaderCallback,
ShapeBorderClipper,
SingleChildLayoutDelegate,
StackFit,
SystemMouseCursors,
TextOverflow,
ValueChanged,
ValueGetter,
WrapAlignment,
WrapCrossAlignment;
export 'package:flutter/services.dart' show
AssetBundle;
// Examples can assume:
// class TestWidget extends StatelessWidget { const TestWidget({super.key}); @override Widget build(BuildContext context) => const Placeholder(); }
// late WidgetTester tester;
// late bool _visible;
// class Sky extends CustomPainter { @override void paint(Canvas c, Size s) {} @override bool shouldRepaint(Sky s) => false; }
// late BuildContext context;
// String userAvatarUrl = '';
// BIDIRECTIONAL TEXT SUPPORT
/// An [InheritedElement] that has hundreds of dependencies but will
/// infrequently change. This provides a performance tradeoff where building
/// the [Widget]s is faster but performing updates is slower.
///
/// | | _UbiquitousInheritedElement | InheritedElement |
/// |---------------------|------------------------------|------------------|
/// | insert (best case) | O(1) | O(1) |
/// | insert (worst case) | O(1) | O(n) |
/// | search (best case) | O(n) | O(1) |
/// | search (worst case) | O(n) | O(n) |
///
/// Insert happens when building the [Widget] tree, search happens when updating
/// [Widget]s.
class _UbiquitousInheritedElement extends InheritedElement {
/// Creates an element that uses the given widget as its configuration.
_UbiquitousInheritedElement(super.widget);
@override
void setDependencies(Element dependent, Object? value) {
// This is where the cost of [InheritedElement] is incurred during build
// time of the widget tree. Omitting this bookkeeping is where the
// performance savings come from.
assert(value == null);
}
@override
Object? getDependencies(Element dependent) {
return null;
}
@override
void notifyClients(InheritedWidget oldWidget) {
_recurseChildren(this, (Element element) {
if (element.doesDependOnInheritedElement(this)) {
notifyDependent(oldWidget, element);
}
});
}
static void _recurseChildren(Element element, ElementVisitor visitor) {
element.visitChildren((Element child) {
_recurseChildren(child, visitor);
});
visitor(element);
}
}
/// See also:
///
/// * [_UbiquitousInheritedElement], the [Element] for [_UbiquitousInheritedWidget].
abstract class _UbiquitousInheritedWidget extends InheritedWidget {
const _UbiquitousInheritedWidget({super.key, required super.child});
@override
InheritedElement createElement() => _UbiquitousInheritedElement(this);
}
/// A widget that determines the ambient directionality of text and
/// text-direction-sensitive render objects.
///
/// For example, [Padding] depends on the [Directionality] to resolve
/// [EdgeInsetsDirectional] objects into absolute [EdgeInsets] objects.
class Directionality extends _UbiquitousInheritedWidget {
/// Creates a widget that determines the directionality of text and
/// text-direction-sensitive render objects.
///
/// The [textDirection] and [child] arguments must not be null.
const Directionality({
super.key,
required this.textDirection,
required super.child,
}) : assert(textDirection != null),
assert(child != null);
/// The text direction for this subtree.
final TextDirection textDirection;
/// The text direction from the closest instance of this class that encloses
/// the given context.
///
/// If there is no [Directionality] ancestor widget in the tree at the given
/// context, then this will throw a descriptive [FlutterError] in debug mode
/// and an exception in release mode.
///
/// Typical usage is as follows:
///
/// ```dart
/// TextDirection textDirection = Directionality.of(context);
/// ```
///
/// See also:
///
/// * [maybeOf], which will return null if no [Directionality] ancestor
/// widget is in the tree.
static TextDirection of(BuildContext context) {
assert(debugCheckHasDirectionality(context));
final Directionality widget = context.dependOnInheritedWidgetOfExactType<Directionality>()!;
return widget.textDirection;
}
/// The text direction from the closest instance of this class that encloses
/// the given context.
///
/// If there is no [Directionality] ancestor widget in the tree at the given
/// context, then this will return null.
///
/// Typical usage is as follows:
///
/// ```dart
/// TextDirection? textDirection = Directionality.maybeOf(context);
/// ```
///
/// See also:
///
/// * [of], which will throw if no [Directionality] ancestor widget is in the
/// tree.
static TextDirection? maybeOf(BuildContext context) {
final Directionality? widget = context.dependOnInheritedWidgetOfExactType<Directionality>();
return widget?.textDirection;
}
@override
bool updateShouldNotify(Directionality oldWidget) => textDirection != oldWidget.textDirection;
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(EnumProperty<TextDirection>('textDirection', textDirection));
}
}
// PAINTING NODES
/// A widget that makes its child partially transparent.
///
/// This class paints its child into an intermediate buffer and then blends the
/// child back into the scene partially transparent.
///
/// For values of opacity other than 0.0 and 1.0, this class is relatively
/// expensive because it requires painting the child into an intermediate
/// buffer. For the value 0.0, the child is simply not painted at all. For the
/// value 1.0, the child is painted immediately without an intermediate buffer.
///
/// The presence of the intermediate buffer which has a transparent background
/// by default may cause some child widgets to behave differently. For example
/// a [BackdropFilter] child will only be able to apply its filter to the content
/// between this widget and the backdrop child and may require adjusting the
/// [BackdropFilter.blendMode] property to produce the desired results.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=9hltevOHQBw}
///
/// {@tool snippet}
///
/// This example shows some [Text] when the `_visible` member field is true, and
/// hides it when it is false:
///
/// ```dart
/// Opacity(
/// opacity: _visible ? 1.0 : 0.0,
/// child: const Text("Now you see me, now you don't!"),
/// )
/// ```
/// {@end-tool}
///
/// This is more efficient than adding and removing the child widget from the
/// tree on demand.
///
/// ## Performance considerations for opacity animation
///
/// Animating an [Opacity] widget directly causes the widget (and possibly its
/// subtree) to rebuild each frame, which is not very efficient. Consider using
/// an [AnimatedOpacity] or a [FadeTransition] instead.
///
/// ## Transparent image
///
/// If only a single [Image] or [Color] needs to be composited with an opacity
/// between 0.0 and 1.0, it's much faster to directly use them without [Opacity]
/// widgets.
///
/// For example, `Container(color: Color.fromRGBO(255, 0, 0, 0.5))` is much
/// faster than `Opacity(opacity: 0.5, child: Container(color: Colors.red))`.
///
/// {@tool snippet}
///
/// The following example draws an [Image] with 0.5 opacity without using
/// [Opacity]:
///
/// ```dart
/// Image.network(
/// 'https://raw.githubusercontent.com/flutter/assets-for-api-docs/master/packages/diagrams/assets/blend_mode_destination.jpeg',
/// color: const Color.fromRGBO(255, 255, 255, 0.5),
/// colorBlendMode: BlendMode.modulate
/// )
/// ```
///
/// {@end-tool}
///
/// Directly drawing an [Image] or [Color] with opacity is faster than using
/// [Opacity] on top of them because [Opacity] could apply the opacity to a
/// group of widgets and therefore a costly offscreen buffer will be used.
/// Drawing content into the offscreen buffer may also trigger render target
/// switches and such switching is particularly slow in older GPUs.
///
/// See also:
///
/// * [Visibility], which can hide a child more efficiently (albeit less
/// subtly, because it is either visible or hidden, rather than allowing
/// fractional opacity values). Specifically, the [Visibility.maintain]
/// constructor is equivalent to using an opacity widget with values of
/// `0.0` or `1.0`.
/// * [ShaderMask], which can apply more elaborate effects to its child.
/// * [Transform], which applies an arbitrary transform to its child widget at
/// paint time.
/// * [AnimatedOpacity], which uses an animation internally to efficiently
/// animate opacity.
/// * [FadeTransition], which uses a provided animation to efficiently animate
/// opacity.
/// * [Image], which can directly provide a partially transparent image with
/// much less performance hit.
class Opacity extends SingleChildRenderObjectWidget {
/// Creates a widget that makes its child partially transparent.
///
/// The [opacity] argument must not be null and must be between 0.0 and 1.0
/// (inclusive).
const Opacity({
super.key,
required this.opacity,
this.alwaysIncludeSemantics = false,
super.child,
}) : assert(opacity != null && opacity >= 0.0 && opacity <= 1.0),
assert(alwaysIncludeSemantics != null);
/// The fraction to scale the child's alpha value.
///
/// An opacity of 1.0 is fully opaque. An opacity of 0.0 is fully transparent
/// (i.e., invisible).
///
/// The opacity must not be null.
///
/// Values 1.0 and 0.0 are painted with a fast path. Other values
/// require painting the child into an intermediate buffer, which is
/// expensive.
final double opacity;
/// Whether the semantic information of the children is always included.
///
/// Defaults to false.
///
/// When true, regardless of the opacity settings the child semantic
/// information is exposed as if the widget were fully visible. This is
/// useful in cases where labels may be hidden during animations that
/// would otherwise contribute relevant semantics.
final bool alwaysIncludeSemantics;
@override
RenderOpacity createRenderObject(BuildContext context) {
return RenderOpacity(
opacity: opacity,
alwaysIncludeSemantics: alwaysIncludeSemantics,
);
}
@override
void updateRenderObject(BuildContext context, RenderOpacity renderObject) {
renderObject
..opacity = opacity
..alwaysIncludeSemantics = alwaysIncludeSemantics;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DoubleProperty('opacity', opacity));
properties.add(FlagProperty('alwaysIncludeSemantics', value: alwaysIncludeSemantics, ifTrue: 'alwaysIncludeSemantics'));
}
}
/// A widget that applies a mask generated by a [Shader] to its child.
///
/// For example, [ShaderMask] can be used to gradually fade out the edge
/// of a child by using a [ui.Gradient.linear] mask.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=7sUL66pTQ7Q}
///
/// {@tool snippet}
///
/// This example makes the text look like it is on fire:
///
/// ```dart
/// ShaderMask(
/// shaderCallback: (Rect bounds) {
/// return RadialGradient(
/// center: Alignment.topLeft,
/// radius: 1.0,
/// colors: <Color>[Colors.yellow, Colors.deepOrange.shade900],
/// tileMode: TileMode.mirror,
/// ).createShader(bounds);
/// },
/// child: const Text('I’m burning the memories'),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [Opacity], which can apply a uniform alpha effect to its child.
/// * [CustomPaint], which lets you draw directly on the canvas.
/// * [DecoratedBox], for another approach at decorating child widgets.
/// * [BackdropFilter], which applies an image filter to the background.
class ShaderMask extends SingleChildRenderObjectWidget {
/// Creates a widget that applies a mask generated by a [Shader] to its child.
///
/// The [shaderCallback] and [blendMode] arguments must not be null.
const ShaderMask({
super.key,
required this.shaderCallback,
this.blendMode = BlendMode.modulate,
super.child,
}) : assert(shaderCallback != null),
assert(blendMode != null);
/// Called to create the [dart:ui.Shader] that generates the mask.
///
/// The shader callback is called with the current size of the child so that
/// it can customize the shader to the size and location of the child.
///
/// Typically this will use a [LinearGradient], [RadialGradient], or
/// [SweepGradient] to create the [dart:ui.Shader], though the
/// [dart:ui.ImageShader] class could also be used.
final ShaderCallback shaderCallback;
/// The [BlendMode] to use when applying the shader to the child.
///
/// The default, [BlendMode.modulate], is useful for applying an alpha blend
/// to the child. Other blend modes can be used to create other effects.
final BlendMode blendMode;
@override
RenderShaderMask createRenderObject(BuildContext context) {
return RenderShaderMask(
shaderCallback: shaderCallback,
blendMode: blendMode,
);
}
@override
void updateRenderObject(BuildContext context, RenderShaderMask renderObject) {
renderObject
..shaderCallback = shaderCallback
..blendMode = blendMode;
}
}
/// A widget that applies a filter to the existing painted content and then
/// paints [child].
///
/// The filter will be applied to all the area within its parent or ancestor
/// widget's clip. If there's no clip, the filter will be applied to the full
/// screen.
///
/// The results of the filter will be blended back into the background using
/// the [blendMode] parameter.
/// {@template flutter.widgets.BackdropFilter.blendMode}
/// The only value for [blendMode] that is supported on all platforms is
/// [BlendMode.srcOver] which works well for most scenes. But that value may
/// produce surprising results when a parent of the [BackdropFilter] uses a
/// temporary buffer, or save layer, as does an [Opacity] widget. In that
/// situation, a value of [BlendMode.src] can produce more pleasing results,
/// but at the cost of incompatibility with some platforms, most notably the
/// html renderer for web applications.
/// {@endtemplate}
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=dYRs7Q1vfYI}
///
/// {@tool snippet}
/// If the [BackdropFilter] needs to be applied to an area that exactly matches
/// its child, wraps the [BackdropFilter] with a clip widget that clips exactly
/// to that child.
///
/// ```dart
/// Stack(
/// fit: StackFit.expand,
/// children: <Widget>[
/// Text('0' * 10000),
/// Center(
/// child: ClipRect( // <-- clips to the 200x200 [Container] below
/// child: BackdropFilter(
/// filter: ui.ImageFilter.blur(
/// sigmaX: 5.0,
/// sigmaY: 5.0,
/// ),
/// child: Container(
/// alignment: Alignment.center,
/// width: 200.0,
/// height: 200.0,
/// child: const Text('Hello World'),
/// ),
/// ),
/// ),
/// ),
/// ],
/// )
/// ```
/// {@end-tool}
///
/// This effect is relatively expensive, especially if the filter is non-local,
/// such as a blur.
///
/// If all you want to do is apply an [ImageFilter] to a single widget
/// (as opposed to applying the filter to everything _beneath_ a widget), use
/// [ImageFiltered] instead. For that scenario, [ImageFiltered] is both
/// easier to use and less expensive than [BackdropFilter].
///
/// {@tool snippet}
///
/// This example shows how the common case of applying a [BackdropFilter] blur
/// to a single sibling can be replaced with an [ImageFiltered] widget. This code
/// is generally simpler and the performance will be improved dramatically for
/// complex filters like blurs.
///
/// The implementation below is unnecessarily expensive.
///
/// ```dart
/// Widget buildBackdrop() {
/// return Stack(
/// children: <Widget>[
/// Positioned.fill(child: Image.asset('image.png')),
/// Positioned.fill(
/// child: BackdropFilter(
/// filter: ui.ImageFilter.blur(sigmaX: 6, sigmaY: 6),
/// ),
/// ),
/// ],
/// );
/// }
/// ```
/// {@end-tool}
/// {@tool snippet}
/// Instead consider the following approach which directly applies a blur
/// to the child widget.
///
/// ```dart
/// Widget buildFilter() {
/// return ImageFiltered(
/// imageFilter: ui.ImageFilter.blur(sigmaX: 6, sigmaY: 6),
/// child: Image.asset('image.png'),
/// );
/// }
/// ```
///
/// {@end-tool}
///
/// See also:
///
/// * [ImageFiltered], which applies an [ImageFilter] to its child.
/// * [DecoratedBox], which draws a background under (or over) a widget.
/// * [Opacity], which changes the opacity of the widget itself.
class BackdropFilter extends SingleChildRenderObjectWidget {
/// Creates a backdrop filter.
///
/// The [filter] argument must not be null.
/// The [blendMode] argument will default to [BlendMode.srcOver] and must not be
/// null if provided.
const BackdropFilter({
super.key,
required this.filter,
super.child,
this.blendMode = BlendMode.srcOver,
}) : assert(filter != null);
/// The image filter to apply to the existing painted content before painting the child.
///
/// For example, consider using [ImageFilter.blur] to create a backdrop
/// blur effect.
final ui.ImageFilter filter;
/// The blend mode to use to apply the filtered background content onto the background
/// surface.
///
/// {@macro flutter.widgets.BackdropFilter.blendMode}
final BlendMode blendMode;
@override
RenderBackdropFilter createRenderObject(BuildContext context) {
return RenderBackdropFilter(filter: filter, blendMode: blendMode);
}
@override
void updateRenderObject(BuildContext context, RenderBackdropFilter renderObject) {
renderObject
..filter = filter
..blendMode = blendMode;
}
}
/// A widget that provides a canvas on which to draw during the paint phase.
///
/// When asked to paint, [CustomPaint] first asks its [painter] to paint on the
/// current canvas, then it paints its child, and then, after painting its
/// child, it asks its [foregroundPainter] to paint. The coordinate system of the
/// canvas matches the coordinate system of the [CustomPaint] object. The
/// painters are expected to paint within a rectangle starting at the origin and
/// encompassing a region of the given size. (If the painters paint outside
/// those bounds, there might be insufficient memory allocated to rasterize the
/// painting commands and the resulting behavior is undefined.) To enforce
/// painting within those bounds, consider wrapping this [CustomPaint] with a
/// [ClipRect] widget.
///
/// Painters are implemented by subclassing [CustomPainter].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=kp14Y4uHpHs}
///
/// Because custom paint calls its painters during paint, you cannot call
/// `setState` or `markNeedsLayout` during the callback (the layout for this
/// frame has already happened).
///
/// Custom painters normally size themselves to their child. If they do not have
/// a child, they attempt to size themselves to the [size], which defaults to
/// [Size.zero]. [size] must not be null.
///
/// [isComplex] and [willChange] are hints to the compositor's raster cache
/// and must not be null.
///
/// {@tool snippet}
///
/// This example shows how the sample custom painter shown at [CustomPainter]
/// could be used in a [CustomPaint] widget to display a background to some
/// text.
///
/// ```dart
/// CustomPaint(
/// painter: Sky(),
/// child: const Center(
/// child: Text(
/// 'Once upon a time...',
/// style: TextStyle(
/// fontSize: 40.0,
/// fontWeight: FontWeight.w900,
/// color: Color(0xFFFFFFFF),
/// ),
/// ),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [CustomPainter], the class to extend when creating custom painters.
/// * [Canvas], the class that a custom painter uses to paint.
class CustomPaint extends SingleChildRenderObjectWidget {
/// Creates a widget that delegates its painting.
const CustomPaint({
super.key,
this.painter,
this.foregroundPainter,
this.size = Size.zero,
this.isComplex = false,
this.willChange = false,
super.child,
}) : assert(size != null),
assert(isComplex != null),
assert(willChange != null),
assert(painter != null || foregroundPainter != null || (!isComplex && !willChange));
/// The painter that paints before the children.
final CustomPainter? painter;
/// The painter that paints after the children.
final CustomPainter? foregroundPainter;
/// The size that this [CustomPaint] should aim for, given the layout
/// constraints, if there is no child.
///
/// Defaults to [Size.zero].
///
/// If there's a child, this is ignored, and the size of the child is used
/// instead.
final Size size;
/// Whether the painting is complex enough to benefit from caching.
///
/// The compositor contains a raster cache that holds bitmaps of layers in
/// order to avoid the cost of repeatedly rendering those layers on each
/// frame. If this flag is not set, then the compositor will apply its own
/// heuristics to decide whether the this layer is complex enough to benefit
/// from caching.
///
/// This flag can't be set to true if both [painter] and [foregroundPainter]
/// are null because this flag will be ignored in such case.
final bool isComplex;
/// Whether the raster cache should be told that this painting is likely
/// to change in the next frame.
///
/// This flag can't be set to true if both [painter] and [foregroundPainter]
/// are null because this flag will be ignored in such case.
final bool willChange;
@override
RenderCustomPaint createRenderObject(BuildContext context) {
return RenderCustomPaint(
painter: painter,
foregroundPainter: foregroundPainter,
preferredSize: size,
isComplex: isComplex,
willChange: willChange,
);
}
@override
void updateRenderObject(BuildContext context, RenderCustomPaint renderObject) {
renderObject
..painter = painter
..foregroundPainter = foregroundPainter
..preferredSize = size
..isComplex = isComplex
..willChange = willChange;
}
@override
void didUnmountRenderObject(RenderCustomPaint renderObject) {
renderObject
..painter = null
..foregroundPainter = null;
}
}
/// A widget that clips its child using a rectangle.
///
/// By default, [ClipRect] prevents its child from painting outside its
/// bounds, but the size and location of the clip rect can be customized using a
/// custom [clipper].
///
/// [ClipRect] is commonly used with these widgets, which commonly paint outside
/// their bounds:
///
/// * [CustomPaint]
/// * [CustomSingleChildLayout]
/// * [CustomMultiChildLayout]
/// * [Align] and [Center] (e.g., if [Align.widthFactor] or
/// [Align.heightFactor] is less than 1.0).
/// * [OverflowBox]
/// * [SizedOverflowBox]
///
/// {@tool snippet}
///
/// For example, by combining a [ClipRect] with an [Align], one can show just
/// the top half of an [Image]:
///
/// ```dart
/// ClipRect(
/// child: Align(
/// alignment: Alignment.topCenter,
/// heightFactor: 0.5,
/// child: Image.network(userAvatarUrl),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [CustomClipper], for information about creating custom clips.
/// * [ClipRRect], for a clip with rounded corners.
/// * [ClipOval], for an elliptical clip.
/// * [ClipPath], for an arbitrarily shaped clip.
class ClipRect extends SingleChildRenderObjectWidget {
/// Creates a rectangular clip.
///
/// If [clipper] is null, the clip will match the layout size and position of
/// the child.
///
/// The [clipBehavior] argument must not be null. If [clipBehavior] is
/// [Clip.none], no clipping will be applied.
const ClipRect({
super.key,
this.clipper,
this.clipBehavior = Clip.hardEdge,
super.child,
}) : assert(clipBehavior != null);
/// If non-null, determines which clip to use.
final CustomClipper<Rect>? clipper;
/// {@macro flutter.rendering.ClipRectLayer.clipBehavior}
///
/// Defaults to [Clip.hardEdge].
final Clip clipBehavior;
@override
RenderClipRect createRenderObject(BuildContext context) {
return RenderClipRect(clipper: clipper, clipBehavior: clipBehavior);
}
@override
void updateRenderObject(BuildContext context, RenderClipRect renderObject) {
renderObject
..clipper = clipper
..clipBehavior = clipBehavior;
}
@override
void didUnmountRenderObject(RenderClipRect renderObject) {
renderObject.clipper = null;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<CustomClipper<Rect>>('clipper', clipper, defaultValue: null));
}
}
/// A widget that clips its child using a rounded rectangle.
///
/// By default, [ClipRRect] uses its own bounds as the base rectangle for the
/// clip, but the size and location of the clip can be customized using a custom
/// [clipper].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=eI43jkQkrvs}
///
/// {@tool dartpad}
/// This example shows various [ClipRRect]s applied to containers.
///
/// ** See code in examples/api/lib/widgets/basic/clip_rrect.0.dart **
/// {@end-tool}
///
/// ## Troubleshooting
///
/// ### Why doesn't my [ClipRRect] child have rounded corners?
///
/// When a [ClipRRect] is bigger than the child it contains, its rounded corners
/// could be drawn in unexpected positions. Make sure that [ClipRRect] and its child
/// have the same bounds (by shrinking the [ClipRRect] with a [FittedBox] or by
/// growing the child).
///
/// {@tool dartpad}
/// This example shows a [ClipRRect] that adds round corners to an image.
///
/// ** See code in examples/api/lib/widgets/basic/clip_rrect.1.dart **
/// {@end-tool}
///
/// See also:
///
/// * [CustomClipper], for information about creating custom clips.
/// * [ClipRect], for more efficient clips without rounded corners.
/// * [ClipOval], for an elliptical clip.
/// * [ClipPath], for an arbitrarily shaped clip.
class ClipRRect extends SingleChildRenderObjectWidget {
/// Creates a rounded-rectangular clip.
///
/// The [borderRadius] defaults to [BorderRadius.zero], i.e. a rectangle with
/// right-angled corners.
///
/// If [clipper] is non-null, then [borderRadius] is ignored.
///
/// The [clipBehavior] argument must not be null. If [clipBehavior] is
/// [Clip.none], no clipping will be applied.
const ClipRRect({
super.key,
this.borderRadius = BorderRadius.zero,
this.clipper,
this.clipBehavior = Clip.antiAlias,
super.child,
}) : assert(borderRadius != null || clipper != null),
assert(clipBehavior != null);
/// The border radius of the rounded corners.
///
/// Values are clamped so that horizontal and vertical radii sums do not
/// exceed width/height.
///
/// This value is ignored if [clipper] is non-null.
final BorderRadiusGeometry? borderRadius;
/// If non-null, determines which clip to use.
final CustomClipper<RRect>? clipper;
/// {@macro flutter.rendering.ClipRectLayer.clipBehavior}
///
/// Defaults to [Clip.antiAlias].
final Clip clipBehavior;
@override
RenderClipRRect createRenderObject(BuildContext context) {
return RenderClipRRect(
borderRadius: borderRadius!,
clipper: clipper,
clipBehavior: clipBehavior,
textDirection: Directionality.maybeOf(context),
);
}
@override
void updateRenderObject(BuildContext context, RenderClipRRect renderObject) {
renderObject
..borderRadius = borderRadius!
..clipBehavior = clipBehavior
..clipper = clipper
..textDirection = Directionality.maybeOf(context);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<BorderRadiusGeometry>('borderRadius', borderRadius, showName: false, defaultValue: null));
properties.add(DiagnosticsProperty<CustomClipper<RRect>>('clipper', clipper, defaultValue: null));
}
}
/// A widget that clips its child using an oval.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=vzWWDO6whIM}
///
/// By default, inscribes an axis-aligned oval into its layout dimensions and
/// prevents its child from painting outside that oval, but the size and
/// location of the clip oval can be customized using a custom [clipper].
///
/// See also:
///
/// * [CustomClipper], for information about creating custom clips.
/// * [ClipRect], for more efficient clips without rounded corners.
/// * [ClipRRect], for a clip with rounded corners.
/// * [ClipPath], for an arbitrarily shaped clip.
class ClipOval extends SingleChildRenderObjectWidget {
/// Creates an oval-shaped clip.
///
/// If [clipper] is null, the oval will be inscribed into the layout size and
/// position of the child.
///
/// The [clipBehavior] argument must not be null. If [clipBehavior] is
/// [Clip.none], no clipping will be applied.
const ClipOval({
super.key,
this.clipper,
this.clipBehavior = Clip.antiAlias,
super.child,
}) : assert(clipBehavior != null);
/// If non-null, determines which clip to use.
///
/// The delegate returns a rectangle that describes the axis-aligned
/// bounding box of the oval. The oval's axes will themselves also
/// be axis-aligned.
///
/// If the [clipper] delegate is null, then the oval uses the
/// widget's bounding box (the layout dimensions of the render
/// object) instead.
final CustomClipper<Rect>? clipper;
/// {@macro flutter.rendering.ClipRectLayer.clipBehavior}
///
/// Defaults to [Clip.antiAlias].
final Clip clipBehavior;
@override
RenderClipOval createRenderObject(BuildContext context) {
return RenderClipOval(clipper: clipper, clipBehavior: clipBehavior);
}
@override
void updateRenderObject(BuildContext context, RenderClipOval renderObject) {
renderObject
..clipper = clipper
..clipBehavior = clipBehavior;
}
@override
void didUnmountRenderObject(RenderClipOval renderObject) {
renderObject.clipper = null;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<CustomClipper<Rect>>('clipper', clipper, defaultValue: null));
}
}
/// A widget that clips its child using a path.
///
/// Calls a callback on a delegate whenever the widget is to be
/// painted. The callback returns a path and the widget prevents the
/// child from painting outside the path.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=oAUebVIb-7s}
///
/// Clipping to a path is expensive. Certain shapes have more
/// optimized widgets:
///
/// * To clip to a rectangle, consider [ClipRect].
/// * To clip to an oval or circle, consider [ClipOval].
/// * To clip to a rounded rectangle, consider [ClipRRect].
///
/// To clip to a particular [ShapeBorder], consider using either the
/// [ClipPath.shape] static method or the [ShapeBorderClipper] custom clipper
/// class.
class ClipPath extends SingleChildRenderObjectWidget {
/// Creates a path clip.
///
/// If [clipper] is null, the clip will be a rectangle that matches the layout
/// size and location of the child. However, rather than use this default,
/// consider using a [ClipRect], which can achieve the same effect more
/// efficiently.
///
/// The [clipBehavior] argument must not be null. If [clipBehavior] is
/// [Clip.none], no clipping will be applied.
const ClipPath({
super.key,
this.clipper,
this.clipBehavior = Clip.antiAlias,
super.child,
}) : assert(clipBehavior != null);
/// Creates a shape clip.
///
/// Uses a [ShapeBorderClipper] to configure the [ClipPath] to clip to the
/// given [ShapeBorder].
static Widget shape({
Key? key,
required ShapeBorder shape,
Clip clipBehavior = Clip.antiAlias,
Widget? child,
}) {
assert(clipBehavior != null);
assert(shape != null);
return Builder(
key: key,
builder: (BuildContext context) {
return ClipPath(
clipper: ShapeBorderClipper(
shape: shape,
textDirection: Directionality.maybeOf(context),
),
clipBehavior: clipBehavior,
child: child,
);
},
);
}
/// If non-null, determines which clip to use.
///
/// The default clip, which is used if this property is null, is the
/// bounding box rectangle of the widget. [ClipRect] is a more
/// efficient way of obtaining that effect.
final CustomClipper<Path>? clipper;
/// {@macro flutter.rendering.ClipRectLayer.clipBehavior}
///
/// Defaults to [Clip.antiAlias].
final Clip clipBehavior;
@override
RenderClipPath createRenderObject(BuildContext context) {
return RenderClipPath(clipper: clipper, clipBehavior: clipBehavior);
}
@override
void updateRenderObject(BuildContext context, RenderClipPath renderObject) {
renderObject
..clipper = clipper
..clipBehavior = clipBehavior;
}
@override
void didUnmountRenderObject(RenderClipPath renderObject) {
renderObject.clipper = null;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<CustomClipper<Path>>('clipper', clipper, defaultValue: null));
}
}
/// A widget representing a physical layer that clips its children to a shape.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=XgUOSS30OQk}
///
/// Physical layers cast shadows based on an [elevation] which is nominally in
/// logical pixels, coming vertically out of the rendering surface.
///
/// For shapes that cannot be expressed as a rectangle with rounded corners use
/// [PhysicalShape].
///
/// See also:
///
/// * [AnimatedPhysicalModel], which animates property changes smoothly over
/// a given duration.
/// * [DecoratedBox], which can apply more arbitrary shadow effects.
/// * [ClipRect], which applies a clip to its child.
class PhysicalModel extends SingleChildRenderObjectWidget {
/// Creates a physical model with a rounded-rectangular clip.
///
/// The [color] is required; physical things have a color.
///
/// The [shape], [elevation], [color], [clipBehavior], and [shadowColor] must
/// not be null. Additionally, the [elevation] must be non-negative.
const PhysicalModel({
super.key,
this.shape = BoxShape.rectangle,
this.clipBehavior = Clip.none,
this.borderRadius,
this.elevation = 0.0,
required this.color,
this.shadowColor = const Color(0xFF000000),
super.child,
}) : assert(shape != null),
assert(elevation != null && elevation >= 0.0),
assert(color != null),
assert(shadowColor != null),
assert(clipBehavior != null);
/// The type of shape.
final BoxShape shape;
/// {@macro flutter.material.Material.clipBehavior}
///
/// Defaults to [Clip.none].
final Clip clipBehavior;
/// The border radius of the rounded corners.
///
/// Values are clamped so that horizontal and vertical radii sums do not
/// exceed width/height.
///
/// This is ignored if the [shape] is not [BoxShape.rectangle].
final BorderRadius? borderRadius;
/// The z-coordinate relative to the parent at which to place this physical
/// object.
///
/// The value is non-negative.
final double elevation;
/// The background color.
final Color color;
/// The shadow color.
final Color shadowColor;
@override
RenderPhysicalModel createRenderObject(BuildContext context) {
return RenderPhysicalModel(
shape: shape,
clipBehavior: clipBehavior,
borderRadius: borderRadius,
elevation: elevation,
color: color,
shadowColor: shadowColor,
);
}
@override
void updateRenderObject(BuildContext context, RenderPhysicalModel renderObject) {
renderObject
..shape = shape
..clipBehavior = clipBehavior
..borderRadius = borderRadius
..elevation = elevation
..color = color
..shadowColor = shadowColor;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(EnumProperty<BoxShape>('shape', shape));
properties.add(DiagnosticsProperty<BorderRadius>('borderRadius', borderRadius));
properties.add(DoubleProperty('elevation', elevation));
properties.add(ColorProperty('color', color));
properties.add(ColorProperty('shadowColor', shadowColor));
}
}
/// A widget representing a physical layer that clips its children to a path.
///
/// Physical layers cast shadows based on an [elevation] which is nominally in
/// logical pixels, coming vertically out of the rendering surface.
///
/// [PhysicalModel] does the same but only supports shapes that can be expressed
/// as rectangles with rounded corners.
///
/// {@tool dartpad}
/// This example shows how to use a [PhysicalShape] on a centered [SizedBox]
/// to clip it to a rounded rectangle using a [ShapeBorderClipper] and give it
/// an orange color along with a shadow.
///
/// ** See code in examples/api/lib/widgets/basic/physical_shape.0.dart **
/// {@end-tool}
///
/// See also:
///
/// * [ShapeBorderClipper], which converts a [ShapeBorder] to a [CustomClipper], as
/// needed by this widget.
class PhysicalShape extends SingleChildRenderObjectWidget {
/// Creates a physical model with an arbitrary shape clip.
///
/// The [color] is required; physical things have a color.
///
/// The [clipper], [elevation], [color], [clipBehavior], and [shadowColor]
/// must not be null. Additionally, the [elevation] must be non-negative.
const PhysicalShape({
super.key,
required this.clipper,
this.clipBehavior = Clip.none,
this.elevation = 0.0,
required this.color,
this.shadowColor = const Color(0xFF000000),
super.child,
}) : assert(clipper != null),
assert(clipBehavior != null),
assert(elevation != null && elevation >= 0.0),
assert(color != null),
assert(shadowColor != null);
/// Determines which clip to use.
///
/// If the path in question is expressed as a [ShapeBorder] subclass,
/// consider using the [ShapeBorderClipper] delegate class to adapt the
/// shape for use with this widget.
final CustomClipper<Path> clipper;
/// {@macro flutter.material.Material.clipBehavior}
///
/// Defaults to [Clip.none].
final Clip clipBehavior;
/// The z-coordinate relative to the parent at which to place this physical
/// object.
///
/// The value is non-negative.
final double elevation;
/// The background color.
final Color color;
/// When elevation is non zero the color to use for the shadow color.
final Color shadowColor;
@override
RenderPhysicalShape createRenderObject(BuildContext context) {
return RenderPhysicalShape(
clipper: clipper,
clipBehavior: clipBehavior,
elevation: elevation,
color: color,
shadowColor: shadowColor,
);
}
@override
void updateRenderObject(BuildContext context, RenderPhysicalShape renderObject) {
renderObject
..clipper = clipper
..clipBehavior = clipBehavior
..elevation = elevation
..color = color
..shadowColor = shadowColor;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<CustomClipper<Path>>('clipper', clipper));
properties.add(DoubleProperty('elevation', elevation));
properties.add(ColorProperty('color', color));
properties.add(ColorProperty('shadowColor', shadowColor));
}
}
// POSITIONING AND SIZING NODES
/// A widget that applies a transformation before painting its child.
///
/// Unlike [RotatedBox], which applies a rotation prior to layout, this object
/// applies its transformation just prior to painting, which means the
/// transformation is not taken into account when calculating how much space
/// this widget's child (and thus this widget) consumes.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=9z_YNlRlWfA}
///
/// {@tool snippet}
///
/// This example rotates and skews an orange box containing text, keeping the
/// top right corner pinned to its original position.
///
/// ```dart
/// Container(
/// color: Colors.black,
/// child: Transform(
/// alignment: Alignment.topRight,
/// transform: Matrix4.skewY(0.3)..rotateZ(-math.pi / 12.0),
/// child: Container(
/// padding: const EdgeInsets.all(8.0),
/// color: const Color(0xFFE8581C),
/// child: const Text('Apartment for rent!'),
/// ),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [RotatedBox], which rotates the child widget during layout, not just
/// during painting.
/// * [FractionalTranslation], which applies a translation to the child
/// that is relative to the child's size.
/// * [FittedBox], which sizes and positions its child widget to fit the parent
/// according to a given [BoxFit] discipline.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class Transform extends SingleChildRenderObjectWidget {
/// Creates a widget that transforms its child.
///
/// The [transform] argument must not be null.
const Transform({
super.key,
required this.transform,
this.origin,
this.alignment,
this.transformHitTests = true,
this.filterQuality,
super.child,
}) : assert(transform != null);
/// Creates a widget that transforms its child using a rotation around the
/// center.
///
/// The `angle` argument must not be null. It gives the rotation in clockwise
/// radians.
///
/// {@tool snippet}
///
/// This example rotates an orange box containing text around its center by
/// fifteen degrees.
///
/// ```dart
/// Transform.rotate(
/// angle: -math.pi / 12.0,
/// child: Container(
/// padding: const EdgeInsets.all(8.0),
/// color: const Color(0xFFE8581C),
/// child: const Text('Apartment for rent!'),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [RotationTransition], which animates changes in rotation smoothly
/// over a given duration.
Transform.rotate({
super.key,
required double angle,
this.origin,
this.alignment = Alignment.center,
this.transformHitTests = true,
this.filterQuality,
super.child,
}) : transform = _computeRotation(angle);
/// Creates a widget that transforms its child using a translation.
///
/// The `offset` argument must not be null. It specifies the translation.
///
/// {@tool snippet}
///
/// This example shifts the silver-colored child down by fifteen pixels.
///
/// ```dart
/// Transform.translate(
/// offset: const Offset(0.0, 15.0),
/// child: Container(
/// padding: const EdgeInsets.all(8.0),
/// color: const Color(0xFF7F7F7F),
/// child: const Text('Quarter'),
/// ),
/// )
/// ```
/// {@end-tool}
Transform.translate({
super.key,
required Offset offset,
this.transformHitTests = true,
this.filterQuality,
super.child,
}) : transform = Matrix4.translationValues(offset.dx, offset.dy, 0.0),
origin = null,
alignment = null;
/// Creates a widget that scales its child along the 2D plane.
///
/// The `scaleX` argument provides the scalar by which to multiply the `x` axis, and the `scaleY` argument provides the scalar by which to multiply the `y` axis. Either may be omitted, in which case that axis defaults to 1.0.
///
/// For convenience, to scale the child uniformly, instead of providing `scaleX` and `scaleY`, the `scale` parameter may be used.
///
/// At least one of `scale`, `scaleX`, and `scaleY` must be non-null. If `scale` is provided, the other two must be null; similarly, if it is not provided, one of the other two must be provided.
///
/// The [alignment] controls the origin of the scale; by default, this is
/// the center of the box.
///
/// {@tool snippet}
///
/// This example shrinks an orange box containing text such that each dimension
/// is half the size it would otherwise be.
///
/// ```dart
/// Transform.scale(
/// scale: 0.5,
/// child: Container(
/// padding: const EdgeInsets.all(8.0),
/// color: const Color(0xFFE8581C),
/// child: const Text('Bad Idea Bears'),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [ScaleTransition], which animates changes in scale smoothly
/// over a given duration.
Transform.scale({
super.key,
double? scale,
double? scaleX,
double? scaleY,
this.origin,
this.alignment = Alignment.center,
this.transformHitTests = true,
this.filterQuality,
super.child,
}) : assert(!(scale == null && scaleX == null && scaleY == null), "At least one of 'scale', 'scaleX' and 'scaleY' is required to be non-null"),
assert(scale == null || (scaleX == null && scaleY == null), "If 'scale' is non-null then 'scaleX' and 'scaleY' must be left null"),
transform = Matrix4.diagonal3Values(scale ?? scaleX ?? 1.0, scale ?? scaleY ?? 1.0, 1.0);
// Computes a rotation matrix for an angle in radians, attempting to keep rotations
// at integral values for angles of 0, π/2, π, 3π/2.
static Matrix4 _computeRotation(double radians) {
assert(radians.isFinite, 'Cannot compute the rotation matrix for a non-finite angle: $radians');
if (radians == 0.0) {
return Matrix4.identity();
}
final double sin = math.sin(radians);
if (sin == 1.0) {
return _createZRotation(1.0, 0.0);
}
if (sin == -1.0) {
return _createZRotation(-1.0, 0.0);
}
final double cos = math.cos(radians);
if (cos == -1.0) {
return _createZRotation(0.0, -1.0);
}
return _createZRotation(sin, cos);
}
static Matrix4 _createZRotation(double sin, double cos) {
final Matrix4 result = Matrix4.zero();
result.storage[0] = cos;
result.storage[1] = sin;
result.storage[4] = -sin;
result.storage[5] = cos;
result.storage[10] = 1.0;
result.storage[15] = 1.0;
return result;
}
/// The matrix to transform the child by during painting.
final Matrix4 transform;
/// The origin of the coordinate system (relative to the upper left corner of
/// this render object) in which to apply the matrix.
///
/// Setting an origin is equivalent to conjugating the transform matrix by a
/// translation. This property is provided just for convenience.
final Offset? origin;
/// The alignment of the origin, relative to the size of the box.
///
/// This is equivalent to setting an origin based on the size of the box.
/// If it is specified at the same time as the [origin], both are applied.
///
/// An [AlignmentDirectional.centerStart] value is the same as an [Alignment]
/// whose [Alignment.x] value is `-1.0` if [Directionality.of] returns
/// [TextDirection.ltr], and `1.0` if [Directionality.of] returns
/// [TextDirection.rtl]. Similarly [AlignmentDirectional.centerEnd] is the
/// same as an [Alignment] whose [Alignment.x] value is `1.0` if
/// [Directionality.of] returns [TextDirection.ltr], and `-1.0` if
/// [Directionality.of] returns [TextDirection.rtl].
final AlignmentGeometry? alignment;
/// Whether to apply the transformation when performing hit tests.
final bool transformHitTests;
/// The filter quality with which to apply the transform as a bitmap operation.
///
/// {@template flutter.widgets.Transform.optional.FilterQuality}
/// The transform will be applied by re-rendering the child if [filterQuality] is null,
/// otherwise it controls the quality of an [ImageFilter.matrix] applied to a bitmap
/// rendering of the child.
/// {@endtemplate}
final FilterQuality? filterQuality;
@override
RenderTransform createRenderObject(BuildContext context) {
return RenderTransform(
transform: transform,
origin: origin,
alignment: alignment,
textDirection: Directionality.maybeOf(context),
transformHitTests: transformHitTests,
filterQuality: filterQuality,
);
}
@override
void updateRenderObject(BuildContext context, RenderTransform renderObject) {
renderObject
..transform = transform
..origin = origin
..alignment = alignment
..textDirection = Directionality.maybeOf(context)
..transformHitTests = transformHitTests
..filterQuality = filterQuality;
}
}
/// A widget that can be targeted by a [CompositedTransformFollower].
///
/// When this widget is composited during the compositing phase (which comes
/// after the paint phase, as described in [WidgetsBinding.drawFrame]), it
/// updates the [link] object so that any [CompositedTransformFollower] widgets
/// that are subsequently composited in the same frame and were given the same
/// [LayerLink] can position themselves at the same screen location.
///
/// A single [CompositedTransformTarget] can be followed by multiple
/// [CompositedTransformFollower] widgets.
///
/// The [CompositedTransformTarget] must come earlier in the paint order than
/// any linked [CompositedTransformFollower]s.
///
/// See also:
///
/// * [CompositedTransformFollower], the widget that can target this one.
/// * [LeaderLayer], the layer that implements this widget's logic.
class CompositedTransformTarget extends SingleChildRenderObjectWidget {
/// Creates a composited transform target widget.
///
/// The [link] property must not be null, and must not be currently being used
/// by any other [CompositedTransformTarget] object that is in the tree.
const CompositedTransformTarget({
super.key,
required this.link,
super.child,
}) : assert(link != null);
/// The link object that connects this [CompositedTransformTarget] with one or
/// more [CompositedTransformFollower]s.
///
/// This property must not be null. The object must not be associated with
/// another [CompositedTransformTarget] that is also being painted.
final LayerLink link;
@override
RenderLeaderLayer createRenderObject(BuildContext context) {
return RenderLeaderLayer(
link: link,
);
}
@override
void updateRenderObject(BuildContext context, RenderLeaderLayer renderObject) {
renderObject.link = link;
}
}
/// A widget that follows a [CompositedTransformTarget].
///
/// When this widget is composited during the compositing phase (which comes
/// after the paint phase, as described in [WidgetsBinding.drawFrame]), it
/// applies a transformation that brings [targetAnchor] of the linked
/// [CompositedTransformTarget] and [followerAnchor] of this widget together.
/// The two anchor points will have the same global coordinates, unless [offset]
/// is not [Offset.zero], in which case [followerAnchor] will be offset by
/// [offset] in the linked [CompositedTransformTarget]'s coordinate space.
///
/// The [LayerLink] object used as the [link] must be the same object as that
/// provided to the matching [CompositedTransformTarget].
///
/// The [CompositedTransformTarget] must come earlier in the paint order than
/// this [CompositedTransformFollower].
///
/// Hit testing on descendants of this widget will only work if the target
/// position is within the box that this widget's parent considers to be
/// hittable. If the parent covers the screen, this is trivially achievable, so
/// this widget is usually used as the root of an [OverlayEntry] in an app-wide
/// [Overlay] (e.g. as created by the [MaterialApp] widget's [Navigator]).
///
/// See also:
///
/// * [CompositedTransformTarget], the widget that this widget can target.
/// * [FollowerLayer], the layer that implements this widget's logic.
/// * [Transform], which applies an arbitrary transform to a child.
class CompositedTransformFollower extends SingleChildRenderObjectWidget {
/// Creates a composited transform target widget.
///
/// The [link] property must not be null. If it was also provided to a
/// [CompositedTransformTarget], that widget must come earlier in the paint
/// order.
///
/// The [showWhenUnlinked] and [offset] properties must also not be null.
const CompositedTransformFollower({
super.key,
required this.link,
this.showWhenUnlinked = true,
this.offset = Offset.zero,
this.targetAnchor = Alignment.topLeft,
this.followerAnchor = Alignment.topLeft,
super.child,
}) : assert(link != null),
assert(showWhenUnlinked != null),
assert(offset != null),
assert(targetAnchor != null),
assert(followerAnchor != null);
/// The link object that connects this [CompositedTransformFollower] with a
/// [CompositedTransformTarget].
///
/// This property must not be null.
final LayerLink link;
/// Whether to show the widget's contents when there is no corresponding
/// [CompositedTransformTarget] with the same [link].
///
/// When the widget is linked, the child is positioned such that it has the
/// same global position as the linked [CompositedTransformTarget].
///
/// When the widget is not linked, then: if [showWhenUnlinked] is true, the
/// child is visible and not repositioned; if it is false, then child is
/// hidden.
final bool showWhenUnlinked;
/// The anchor point on the linked [CompositedTransformTarget] that
/// [followerAnchor] will line up with.
///
/// {@template flutter.widgets.CompositedTransformFollower.targetAnchor}
/// For example, when [targetAnchor] and [followerAnchor] are both
/// [Alignment.topLeft], this widget will be top left aligned with the linked
/// [CompositedTransformTarget]. When [targetAnchor] is
/// [Alignment.bottomLeft] and [followerAnchor] is [Alignment.topLeft], this
/// widget will be left aligned with the linked [CompositedTransformTarget],
/// and its top edge will line up with the [CompositedTransformTarget]'s
/// bottom edge.
/// {@endtemplate}
///
/// Defaults to [Alignment.topLeft].
final Alignment targetAnchor;
/// The anchor point on this widget that will line up with [targetAnchor] on
/// the linked [CompositedTransformTarget].
///
/// {@macro flutter.widgets.CompositedTransformFollower.targetAnchor}
///
/// Defaults to [Alignment.topLeft].
final Alignment followerAnchor;
/// The additional offset to apply to the [targetAnchor] of the linked
/// [CompositedTransformTarget] to obtain this widget's [followerAnchor]
/// position.
final Offset offset;
@override
RenderFollowerLayer createRenderObject(BuildContext context) {
return RenderFollowerLayer(
link: link,
showWhenUnlinked: showWhenUnlinked,
offset: offset,
leaderAnchor: targetAnchor,
followerAnchor: followerAnchor,
);
}
@override
void updateRenderObject(BuildContext context, RenderFollowerLayer renderObject) {
renderObject
..link = link
..showWhenUnlinked = showWhenUnlinked
..offset = offset
..leaderAnchor = targetAnchor
..followerAnchor = followerAnchor;
}
}
/// Scales and positions its child within itself according to [fit].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=T4Uehk3_wlY}
///
/// {@tool dartpad}
/// In this example, the image is stretched to fill the entire [Container], which would
/// not happen normally without using FittedBox.
///
/// ** See code in examples/api/lib/widgets/basic/fitted_box.0.dart **
/// {@end-tool}
///
/// See also:
///
/// * [Transform], which applies an arbitrary transform to its child widget at
/// paint time.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class FittedBox extends SingleChildRenderObjectWidget {
/// Creates a widget that scales and positions its child within itself according to [fit].
///
/// The [fit] and [alignment] arguments must not be null.
const FittedBox({
super.key,
this.fit = BoxFit.contain,
this.alignment = Alignment.center,
this.clipBehavior = Clip.none,
super.child,
}) : assert(fit != null),
assert(alignment != null),
assert(clipBehavior != null);
/// How to inscribe the child into the space allocated during layout.
final BoxFit fit;
/// How to align the child within its parent's bounds.
///
/// An alignment of (-1.0, -1.0) aligns the child to the top-left corner of its
/// parent's bounds. An alignment of (1.0, 0.0) aligns the child to the middle
/// of the right edge of its parent's bounds.
///
/// Defaults to [Alignment.center].
///
/// See also:
///
/// * [Alignment], a class with convenient constants typically used to
/// specify an [AlignmentGeometry].
/// * [AlignmentDirectional], like [Alignment] for specifying alignments
/// relative to text direction.
final AlignmentGeometry alignment;
/// {@macro flutter.material.Material.clipBehavior}
///
/// Defaults to [Clip.none].
final Clip clipBehavior;
@override
RenderFittedBox createRenderObject(BuildContext context) {
return RenderFittedBox(
fit: fit,
alignment: alignment,
textDirection: Directionality.maybeOf(context),
clipBehavior: clipBehavior,
);
}
@override
void updateRenderObject(BuildContext context, RenderFittedBox renderObject) {
renderObject
..fit = fit
..alignment = alignment
..textDirection = Directionality.maybeOf(context)
..clipBehavior = clipBehavior;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(EnumProperty<BoxFit>('fit', fit));
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
}
}
/// Applies a translation transformation before painting its child.
///
/// The translation is expressed as a [Offset] scaled to the child's size. For
/// example, an [Offset] with a `dx` of 0.25 will result in a horizontal
/// translation of one quarter the width of the child.
///
/// Hit tests will only be detected inside the bounds of the
/// [FractionalTranslation], even if the contents are offset such that
/// they overflow.
///
/// See also:
///
/// * [Transform], which applies an arbitrary transform to its child widget at
/// paint time.
/// * [Transform.translate], which applies an absolute offset translation
/// transformation instead of an offset scaled to the child.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class FractionalTranslation extends SingleChildRenderObjectWidget {
/// Creates a widget that translates its child's painting.
///
/// The [translation] argument must not be null.
const FractionalTranslation({
super.key,
required this.translation,
this.transformHitTests = true,
super.child,
}) : assert(translation != null);
/// The translation to apply to the child, scaled to the child's size.
///
/// For example, an [Offset] with a `dx` of 0.25 will result in a horizontal
/// translation of one quarter the width of the child.
final Offset translation;
/// Whether to apply the translation when performing hit tests.
final bool transformHitTests;
@override
RenderFractionalTranslation createRenderObject(BuildContext context) {
return RenderFractionalTranslation(
translation: translation,
transformHitTests: transformHitTests,
);
}
@override
void updateRenderObject(BuildContext context, RenderFractionalTranslation renderObject) {
renderObject
..translation = translation
..transformHitTests = transformHitTests;
}
}
/// A widget that rotates its child by a integral number of quarter turns.
///
/// Unlike [Transform], which applies a transform just prior to painting,
/// this object applies its rotation prior to layout, which means the entire
/// rotated box consumes only as much space as required by the rotated child.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=BFE6_UglLfQ}
///
/// {@tool snippet}
///
/// This snippet rotates the child (some [Text]) so that it renders from bottom
/// to top, like an axis label on a graph:
///
/// ```dart
/// const RotatedBox(
/// quarterTurns: 3,
/// child: Text('Hello World!'),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [Transform], which is a paint effect that allows you to apply an
/// arbitrary transform to a child.
/// * [Transform.rotate], which applies a rotation paint effect.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class RotatedBox extends SingleChildRenderObjectWidget {
/// A widget that rotates its child.
///
/// The [quarterTurns] argument must not be null.
const RotatedBox({
super.key,
required this.quarterTurns,
super.child,
}) : assert(quarterTurns != null);
/// The number of clockwise quarter turns the child should be rotated.
final int quarterTurns;
@override
RenderRotatedBox createRenderObject(BuildContext context) => RenderRotatedBox(quarterTurns: quarterTurns);
@override
void updateRenderObject(BuildContext context, RenderRotatedBox renderObject) {
renderObject.quarterTurns = quarterTurns;
}
}
/// A widget that insets its child by the given padding.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=oD5RtLhhubg}
///
/// When passing layout constraints to its child, padding shrinks the
/// constraints by the given padding, causing the child to layout at a smaller
/// size. Padding then sizes itself to its child's size, inflated by the
/// padding, effectively creating empty space around the child.
///
/// {@tool snippet}
///
/// This snippet creates "Hello World!" [Text] inside a [Card] that is indented
/// by sixteen pixels in each direction.
///
/// ![](https://flutter.github.io/assets-for-api-docs/assets/widgets/padding.png)
///
/// ```dart
/// const Card(
/// child: Padding(
/// padding: EdgeInsets.all(16.0),
/// child: Text('Hello World!'),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// ## Design discussion
///
/// ### Why use a [Padding] widget rather than a [Container] with a [Container.padding] property?
///
/// There isn't really any difference between the two. If you supply a
/// [Container.padding] argument, [Container] simply builds a [Padding] widget
/// for you.
///
/// [Container] doesn't implement its properties directly. Instead, [Container]
/// combines a number of simpler widgets together into a convenient package. For
/// example, the [Container.padding] property causes the container to build a
/// [Padding] widget and the [Container.decoration] property causes the
/// container to build a [DecoratedBox] widget. If you find [Container]
/// convenient, feel free to use it. If not, feel free to build these simpler
/// widgets in whatever combination meets your needs.
///
/// In fact, the majority of widgets in Flutter are simply combinations of other
/// simpler widgets. Composition, rather than inheritance, is the primary
/// mechanism for building up widgets.
///
/// See also:
///
/// * [AnimatedPadding], which animates changes in [padding] over a given
/// duration.
/// * [EdgeInsets], the class that is used to describe the padding dimensions.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class Padding extends SingleChildRenderObjectWidget {
/// Creates a widget that insets its child.
///
/// The [padding] argument must not be null.
const Padding({
super.key,
required this.padding,
super.child,
}) : assert(padding != null);
/// The amount of space by which to inset the child.
final EdgeInsetsGeometry padding;
@override
RenderPadding createRenderObject(BuildContext context) {
return RenderPadding(
padding: padding,
textDirection: Directionality.maybeOf(context),
);
}
@override
void updateRenderObject(BuildContext context, RenderPadding renderObject) {
renderObject
..padding = padding
..textDirection = Directionality.maybeOf(context);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('padding', padding));
}
}
/// A widget that aligns its child within itself and optionally sizes itself
/// based on the child's size.
///
/// For example, to align a box at the bottom right, you would pass this box a
/// tight constraint that is bigger than the child's natural size,
/// with an alignment of [Alignment.bottomRight].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=g2E7yl3MwMk}
///
/// This widget will be as big as possible if its dimensions are constrained and
/// [widthFactor] and [heightFactor] are null. If a dimension is unconstrained
/// and the corresponding size factor is null then the widget will match its
/// child's size in that dimension. If a size factor is non-null then the
/// corresponding dimension of this widget will be the product of the child's
/// dimension and the size factor. For example if widthFactor is 2.0 then
/// the width of this widget will always be twice its child's width.
///
/// ## How it works
///
/// The [alignment] property describes a point in the `child`'s coordinate system
/// and a different point in the coordinate system of this widget. The [Align]
/// widget positions the `child` such that both points are lined up on top of
/// each other.
///
/// {@tool snippet}
/// The [Align] widget in this example uses one of the defined constants from
/// [Alignment], [Alignment.topRight]. This places the [FlutterLogo] in the top
/// right corner of the parent blue [Container].
///
/// ![A blue square container with the Flutter logo in the top right corner.](https://flutter.github.io/assets-for-api-docs/assets/widgets/align_constant.png)
///
/// ```dart
/// Center(
/// child: Container(
/// height: 120.0,
/// width: 120.0,
/// color: Colors.blue[50],
/// child: const Align(
/// alignment: Alignment.topRight,
/// child: FlutterLogo(
/// size: 60,
/// ),
/// ),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// {@tool snippet}
/// The [Alignment] used in the following example defines a single point:
///
/// * (0.2 * width of [FlutterLogo]/2 + width of [FlutterLogo]/2, 0.6 * height
/// of [FlutterLogo]/2 + height of [FlutterLogo]/2) = (36.0, 48.0).
///
/// The [Alignment] class uses a coordinate system with an origin in the center
/// of the [Container], as shown with the [Icon] above. [Align] will place the
/// [FlutterLogo] at (36.0, 48.0) according to this coordinate system.
///
/// ![A blue square container with the Flutter logo positioned according to the
/// Alignment specified above. A point is marked at the center of the container
/// for the origin of the Alignment coordinate system.](https://flutter.github.io/assets-for-api-docs/assets/widgets/align_alignment.png)
///
/// ```dart
/// Center(
/// child: Container(
/// height: 120.0,
/// width: 120.0,
/// color: Colors.blue[50],
/// child: const Align(
/// alignment: Alignment(0.2, 0.6),
/// child: FlutterLogo(
/// size: 60,
/// ),
/// ),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// {@tool snippet}
/// The [FractionalOffset] used in the following example defines two points:
///
/// * (0.2 * width of [FlutterLogo], 0.6 * height of [FlutterLogo]) = (12.0, 36.0)
/// in the coordinate system of the blue container.
/// * (0.2 * width of [Align], 0.6 * height of [Align]) = (24.0, 72.0) in the
/// coordinate system of the [Align] widget.
///
/// The [Align] widget positions the [FlutterLogo] such that the two points are on
/// top of each other. In this example, the top left of the [FlutterLogo] will
/// be placed at (24.0, 72.0) - (12.0, 36.0) = (12.0, 36.0) from the top left of
/// the [Align] widget.
///
/// The [FractionalOffset] class uses a coordinate system with an origin in the top-left
/// corner of the [Container] in difference to the center-oriented system used in
/// the example above with [Alignment].
///
/// ![A blue square container with the Flutter logo positioned according to the
/// FractionalOffset specified above. A point is marked at the top left corner
/// of the container for the origin of the FractionalOffset coordinate system.](https://flutter.github.io/assets-for-api-docs/assets/widgets/align_fractional_offset.png)
///
/// ```dart
/// Center(
/// child: Container(
/// height: 120.0,
/// width: 120.0,
/// color: Colors.blue[50],
/// child: const Align(
/// alignment: FractionalOffset(0.2, 0.6),
/// child: FlutterLogo(
/// size: 60,
/// ),
/// ),
/// ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [AnimatedAlign], which animates changes in [alignment] smoothly over a
/// given duration.
/// * [CustomSingleChildLayout], which uses a delegate to control the layout of
/// a single child.
/// * [Center], which is the same as [Align] but with the [alignment] always
/// set to [Alignment.center].
/// * [FractionallySizedBox], which sizes its child based on a fraction of its
/// own size and positions the child according to an [Alignment] value.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class Align extends SingleChildRenderObjectWidget {
/// Creates an alignment widget.
///
/// The alignment defaults to [Alignment.center].
const Align({
super.key,
this.alignment = Alignment.center,
this.widthFactor,
this.heightFactor,
super.child,
}) : assert(alignment != null),
assert(widthFactor == null || widthFactor >= 0.0),
assert(heightFactor == null || heightFactor >= 0.0);
/// How to align the child.
///
/// The x and y values of the [Alignment] control the horizontal and vertical
/// alignment, respectively. An x value of -1.0 means that the left edge of
/// the child is aligned with the left edge of the parent whereas an x value
/// of 1.0 means that the right edge of the child is aligned with the right
/// edge of the parent. Other values interpolate (and extrapolate) linearly.
/// For example, a value of 0.0 means that the center of the child is aligned
/// with the center of the parent.
///
/// See also:
///
/// * [Alignment], which has more details and some convenience constants for
/// common positions.
/// * [AlignmentDirectional], which has a horizontal coordinate orientation
/// that depends on the [TextDirection].
final AlignmentGeometry alignment;
/// If non-null, sets its width to the child's width multiplied by this factor.
///
/// Can be both greater and less than 1.0 but must be non-negative.
final double? widthFactor;
/// If non-null, sets its height to the child's height multiplied by this factor.
///
/// Can be both greater and less than 1.0 but must be non-negative.
final double? heightFactor;
@override
RenderPositionedBox createRenderObject(BuildContext context) {
return RenderPositionedBox(
alignment: alignment,
widthFactor: widthFactor,
heightFactor: heightFactor,
textDirection: Directionality.maybeOf(context),
);
}
@override
void updateRenderObject(BuildContext context, RenderPositionedBox renderObject) {
renderObject
..alignment = alignment
..widthFactor = widthFactor
..heightFactor = heightFactor
..textDirection = Directionality.maybeOf(context);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
properties.add(DoubleProperty('widthFactor', widthFactor, defaultValue: null));
properties.add(DoubleProperty('heightFactor', heightFactor, defaultValue: null));
}
}
/// A widget that centers its child within itself.
///
/// This widget will be as big as possible if its dimensions are constrained and
/// [widthFactor] and [heightFactor] are null. If a dimension is unconstrained
/// and the corresponding size factor is null then the widget will match its
/// child's size in that dimension. If a size factor is non-null then the
/// corresponding dimension of this widget will be the product of the child's
/// dimension and the size factor. For example if widthFactor is 2.0 then
/// the width of this widget will always be twice its child's width.
///
/// See also:
///
/// * [Align], which lets you arbitrarily position a child within itself,
/// rather than just centering it.
/// * [Row], a widget that displays its children in a horizontal array.
/// * [Column], a widget that displays its children in a vertical array.
/// * [Container], a convenience widget that combines common painting,
/// positioning, and sizing widgets.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class Center extends Align {
/// Creates a widget that centers its child.
const Center({ super.key, super.widthFactor, super.heightFactor, super.child });
}
/// A widget that defers the layout of its single child to a delegate.
///
/// The delegate can determine the layout constraints for the child and can
/// decide where to position the child. The delegate can also determine the size
/// of the parent, but the size of the parent cannot depend on the size of the
/// child.
///
/// See also:
///
/// * [SingleChildLayoutDelegate], which controls the layout of the child.
/// * [Align], which sizes itself based on its child's size and positions
/// the child according to an [Alignment] value.
/// * [FractionallySizedBox], which sizes its child based on a fraction of its own
/// size and positions the child according to an [Alignment] value.
/// * [CustomMultiChildLayout], which uses a delegate to position multiple
/// children.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class CustomSingleChildLayout extends SingleChildRenderObjectWidget {
/// Creates a custom single child layout.
///
/// The [delegate] argument must not be null.
const CustomSingleChildLayout({
super.key,
required this.delegate,
super.child,
}) : assert(delegate != null);
/// The delegate that controls the layout of the child.
final SingleChildLayoutDelegate delegate;
@override
RenderCustomSingleChildLayoutBox createRenderObject(BuildContext context) {
return RenderCustomSingleChildLayoutBox(delegate: delegate);
}
@override
void updateRenderObject(BuildContext context, RenderCustomSingleChildLayoutBox renderObject) {
renderObject.delegate = delegate;
}
}
/// Metadata for identifying children in a [CustomMultiChildLayout].
///
/// The [MultiChildLayoutDelegate.hasChild],
/// [MultiChildLayoutDelegate.layoutChild], and
/// [MultiChildLayoutDelegate.positionChild] methods use these identifiers.
class LayoutId extends ParentDataWidget<MultiChildLayoutParentData> {
/// Marks a child with a layout identifier.
///
/// Both the child and the id arguments must not be null.
LayoutId({
Key? key,
required this.id,
required super.child,
}) : assert(child != null),
assert(id != null),
super(key: key ?? ValueKey<Object>(id));
/// An object representing the identity of this child.
///
/// The [id] needs to be unique among the children that the
/// [CustomMultiChildLayout] manages.
final Object id;
@override
void applyParentData(RenderObject renderObject) {
assert(renderObject.parentData is MultiChildLayoutParentData);
final MultiChildLayoutParentData parentData = renderObject.parentData! as MultiChildLayoutParentData;
if (parentData.id != id) {
parentData.id = id;
final AbstractNode? targetParent = renderObject.parent;
if (targetParent is RenderObject) {
targetParent.markNeedsLayout();
}
}
}
@override
Type get debugTypicalAncestorWidgetClass => CustomMultiChildLayout;
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<Object>('id', id));
}
}
/// A widget that uses a delegate to size and position multiple children.
///
/// The delegate can determine the layout constraints for each child and can
/// decide where to position each child. The delegate can also determine the
/// size of the parent, but the size of the parent cannot depend on the sizes of
/// the children.
///
/// [CustomMultiChildLayout] is appropriate when there are complex relationships
/// between the size and positioning of multiple widgets. To control the
/// layout of a single child, [CustomSingleChildLayout] is more appropriate. For
/// simple cases, such as aligning a widget to one or another edge, the [Stack]
/// widget is more appropriate.
///
/// Each child must be wrapped in a [LayoutId] widget to identify the widget for
/// the delegate.
///
/// {@tool dartpad}
/// This example shows a [CustomMultiChildLayout] widget being used to lay out
/// colored blocks from start to finish in a cascade that has some overlap.
///
/// It responds to changes in [Directionality] by re-laying out its children.
///
/// ** See code in examples/api/lib/widgets/basic/custom_multi_child_layout.0.dart **
/// {@end-tool}
///
/// See also:
///
/// * [MultiChildLayoutDelegate], for details about how to control the layout of
/// the children.
/// * [CustomSingleChildLayout], which uses a delegate to control the layout of
/// a single child.
/// * [Stack], which arranges children relative to the edges of the container.
/// * [Flow], which provides paint-time control of its children using transform
/// matrices.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class CustomMultiChildLayout extends MultiChildRenderObjectWidget {
/// Creates a custom multi-child layout.
///
/// The [delegate] argument must not be null.
CustomMultiChildLayout({
super.key,
required this.delegate,
super.children,
}) : assert(delegate != null);
/// The delegate that controls the layout of the children.
final MultiChildLayoutDelegate delegate;
@override
RenderCustomMultiChildLayoutBox createRenderObject(BuildContext context) {
return RenderCustomMultiChildLayoutBox(delegate: delegate);
}
@override
void updateRenderObject(BuildContext context, RenderCustomMultiChildLayoutBox renderObject) {
renderObject.delegate = delegate;
}
}
/// A box with a specified size.
///
/// If given a child, this widget forces it to have a specific width and/or height.
/// These values will be ignored if this widget's parent does not permit them.
/// For example, this happens if the parent is the screen (forces the child to
/// be the same size as the parent), or another [SizedBox] (forces its child to
/// have a specific width and/or height). This can be remedied by wrapping the
/// child [SizedBox] in a widget that does permit it to be any size up to the
/// size of the parent, such as [Center] or [Align].
///
/// If either the width or height is null, this widget will try to size itself to
/// match the child's size in that dimension. If the child's size depends on the
/// size of its parent, the height and width must be provided.
///
/// If not given a child, [SizedBox] will try to size itself as close to the
/// specified height and width as possible given the parent's constraints. If
/// [height] or [width] is null or unspecified, it will be treated as zero.
///
/// The [SizedBox.expand] constructor can be used to make a [SizedBox] that
/// sizes itself to fit the parent. It is equivalent to setting [width] and
/// [height] to [double.infinity].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=EHPu_DzRfqA}
///
/// {@tool snippet}
///
/// This snippet makes the child widget (a [Card] with some [Text]) have the
/// exact size 200x300, parental constraints permitting:
///
/// ```dart
/// const SizedBox(
/// width: 200.0,
/// height: 300.0,
/// child: Card(child: Text('Hello World!')),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [ConstrainedBox], a more generic version of this class that takes
/// arbitrary [BoxConstraints] instead of an explicit width and height.
/// * [UnconstrainedBox], a container that tries to let its child draw without
/// constraints.
/// * [FractionallySizedBox], a widget that sizes its child to a fraction of
/// the total available space.
/// * [AspectRatio], a widget that attempts to fit within the parent's
/// constraints while also sizing its child to match a given aspect ratio.
/// * [FittedBox], which sizes and positions its child widget to fit the parent
/// according to a given [BoxFit] discipline.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
/// * [Understanding constraints](https://flutter.dev/docs/development/ui/layout/constraints),
/// an in-depth article about layout in Flutter.
class SizedBox extends SingleChildRenderObjectWidget {
/// Creates a fixed size box. The [width] and [height] parameters can be null
/// to indicate that the size of the box should not be constrained in
/// the corresponding dimension.
const SizedBox({ super.key, this.width, this.height, super.child });
/// Creates a box that will become as large as its parent allows.
const SizedBox.expand({ super.key, super.child })
: width = double.infinity,
height = double.infinity;
/// Creates a box that will become as small as its parent allows.
const SizedBox.shrink({ super.key, super.child })
: width = 0.0,
height = 0.0;
/// Creates a box with the specified size.
SizedBox.fromSize({ super.key, super.child, Size? size })
: width = size?.width,
height = size?.height;
/// Creates a box whose [width] and [height] are equal.
const SizedBox.square({super.key, super.child, double? dimension})
: width = dimension,
height = dimension;
/// If non-null, requires the child to have exactly this width.
final double? width;
/// If non-null, requires the child to have exactly this height.
final double? height;
@override
RenderConstrainedBox createRenderObject(BuildContext context) {
return RenderConstrainedBox(
additionalConstraints: _additionalConstraints,
);
}
BoxConstraints get _additionalConstraints {
return BoxConstraints.tightFor(width: width, height: height);
}
@override
void updateRenderObject(BuildContext context, RenderConstrainedBox renderObject) {
renderObject.additionalConstraints = _additionalConstraints;
}
@override
String toStringShort() {
final String type;
if (width == double.infinity && height == double.infinity) {
type = '${objectRuntimeType(this, 'SizedBox')}.expand';
} else if (width == 0.0 && height == 0.0) {
type = '${objectRuntimeType(this, 'SizedBox')}.shrink';
} else {
type = objectRuntimeType(this, 'SizedBox');
}
return key == null ? type : '$type-$key';
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
final DiagnosticLevel level;
if ((width == double.infinity && height == double.infinity) ||
(width == 0.0 && height == 0.0)) {
level = DiagnosticLevel.hidden;
} else {
level = DiagnosticLevel.info;
}
properties.add(DoubleProperty('width', width, defaultValue: null, level: level));
properties.add(DoubleProperty('height', height, defaultValue: null, level: level));
}
}
/// A widget that imposes additional constraints on its child.
///
/// For example, if you wanted [child] to have a minimum height of 50.0 logical
/// pixels, you could use `const BoxConstraints(minHeight: 50.0)` as the
/// [constraints].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=o2KveVr7adg}
///
/// {@tool snippet}
///
/// This snippet makes the child widget (a [Card] with some [Text]) fill the
/// parent, by applying [BoxConstraints.expand] constraints:
///
/// ```dart
/// ConstrainedBox(
/// constraints: const BoxConstraints.expand(),
/// child: const Card(child: Text('Hello World!')),
/// )
/// ```
/// {@end-tool}
///
/// The same behavior can be obtained using the [SizedBox.expand] widget.
///
/// See also:
///
/// * [BoxConstraints], the class that describes constraints.
/// * [UnconstrainedBox], a container that tries to let its child draw without
/// constraints.
/// * [SizedBox], which lets you specify tight constraints by explicitly
/// specifying the height or width.
/// * [FractionallySizedBox], which sizes its child based on a fraction of its
/// own size and positions the child according to an [Alignment] value.
/// * [AspectRatio], a widget that attempts to fit within the parent's
/// constraints while also sizing its child to match a given aspect ratio.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class ConstrainedBox extends SingleChildRenderObjectWidget {
/// Creates a widget that imposes additional constraints on its child.
///
/// The [constraints] argument must not be null.
ConstrainedBox({
super.key,
required this.constraints,
super.child,
}) : assert(constraints != null),
assert(constraints.debugAssertIsValid());
/// The additional constraints to impose on the child.
final BoxConstraints constraints;
@override
RenderConstrainedBox createRenderObject(BuildContext context) {
return RenderConstrainedBox(additionalConstraints: constraints);
}
@override
void updateRenderObject(BuildContext context, RenderConstrainedBox renderObject) {
renderObject.additionalConstraints = constraints;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<BoxConstraints>('constraints', constraints, showName: false));
}
}
/// A container widget that applies an arbitrary transform to its constraints,
/// and sizes its child using the resulting [BoxConstraints], optionally
/// clipping, or treating the overflow as an error.
///
/// This container sizes its child using a [BoxConstraints] created by applying
/// [constraintsTransform] to its own constraints. This container will then
/// attempt to adopt the same size, within the limits of its own constraints. If
/// it ends up with a different size, it will align the child based on
/// [alignment]. If the container cannot expand enough to accommodate the entire
/// child, the child will be clipped if [clipBehavior] is not [Clip.none].
///
/// In debug mode, if [clipBehavior] is [Clip.none] and the child overflows the
/// container, a warning will be printed on the console, and black and yellow
/// striped areas will appear where the overflow occurs.
///
/// When [child] is null, this widget becomes as small as possible and never
/// overflows.
///
/// This widget can be used to ensure some of [child]'s natural dimensions are
/// honored, and get an early warning otherwise during development. For
/// instance, if [child] requires a minimum height to fully display its content,
/// [constraintsTransform] can be set to [maxHeightUnconstrained], so that if
/// the parent [RenderObject] fails to provide enough vertical space, a warning
/// will be displayed in debug mode, while still allowing [child] to grow
/// vertically:
///
/// {@tool snippet}
/// In the following snippet, the [Card] is guaranteed to be at least as tall as
/// its "natural" height. Unlike [UnconstrainedBox], it will become taller if
/// its "natural" height is smaller than 40 px. If the [Container] isn't high
/// enough to show the full content of the [Card], in debug mode a warning will
/// be given.
///
/// ```dart
/// Container(
/// constraints: const BoxConstraints(minHeight: 40, maxHeight: 100),
/// alignment: Alignment.center,
/// child: const ConstraintsTransformBox(
/// constraintsTransform: ConstraintsTransformBox.maxHeightUnconstrained,
/// child: Card(child: Text('Hello World!')),
/// )
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [ConstrainedBox], which renders a box which imposes constraints
/// on its child.
/// * [OverflowBox], a widget that imposes additional constraints on its child,
/// and allows the child to overflow itself.
/// * [UnconstrainedBox] which allows its children to render themselves
/// unconstrained and expands to fit them.
class ConstraintsTransformBox extends SingleChildRenderObjectWidget {
/// Creates a widget that uses a function to transform the constraints it
/// passes to its child. If the child overflows the parent's constraints, a
/// warning will be given in debug mode.
///
/// The `debugTransformType` argument adds a debug label to this widget.
///
/// The `alignment`, `clipBehavior` and `constraintsTransform` arguments must
/// not be null.
const ConstraintsTransformBox({
super.key,
super.child,
this.textDirection,
this.alignment = Alignment.center,
required this.constraintsTransform,
this.clipBehavior = Clip.none,
String debugTransformType = '',
}) : _debugTransformLabel = debugTransformType,
assert(alignment != null),
assert(clipBehavior != null),
assert(constraintsTransform != null),
assert(debugTransformType != null);
/// A [BoxConstraintsTransform] that always returns its argument as-is (i.e.,
/// it is an identity function).
///
/// The [ConstraintsTransformBox] becomes a proxy widget that has no effect on
/// layout if [constraintsTransform] is set to this.
static BoxConstraints unmodified(BoxConstraints constraints) => constraints;
/// A [BoxConstraintsTransform] that always returns a [BoxConstraints] that
/// imposes no constraints on either dimension (i.e. `const BoxConstraints()`).
///
/// Setting [constraintsTransform] to this allows [child] to render at its
/// "natural" size (equivalent to an [UnconstrainedBox] with `constrainedAxis`
/// set to null).
static BoxConstraints unconstrained(BoxConstraints constraints) => const BoxConstraints();
/// A [BoxConstraintsTransform] that removes the width constraints from the
/// input.
///
/// Setting [constraintsTransform] to this allows [child] to render at its
/// "natural" width (equivalent to an [UnconstrainedBox] with
/// `constrainedAxis` set to [Axis.horizontal]).
static BoxConstraints widthUnconstrained(BoxConstraints constraints) => constraints.heightConstraints();
/// A [BoxConstraintsTransform] that removes the height constraints from the
/// input.
///
/// Setting [constraintsTransform] to this allows [child] to render at its
/// "natural" height (equivalent to an [UnconstrainedBox] with
/// `constrainedAxis` set to [Axis.vertical]).
static BoxConstraints heightUnconstrained(BoxConstraints constraints) => constraints.widthConstraints();
/// A [BoxConstraintsTransform] that removes the `maxHeight` constraint from
/// the input.
///
/// Setting [constraintsTransform] to this allows [child] to render at its
/// "natural" height or the `minHeight` of the incoming [BoxConstraints],
/// whichever is larger.
static BoxConstraints maxHeightUnconstrained(BoxConstraints constraints) => constraints.copyWith(maxHeight: double.infinity);
/// A [BoxConstraintsTransform] that removes the `maxWidth` constraint from
/// the input.
///
/// Setting [constraintsTransform] to this allows [child] to render at its
/// "natural" width or the `minWidth` of the incoming [BoxConstraints],
/// whichever is larger.
static BoxConstraints maxWidthUnconstrained(BoxConstraints constraints) => constraints.copyWith(maxWidth: double.infinity);
/// A [BoxConstraintsTransform] that removes both the `maxWidth` and the
/// `maxHeight` constraints from the input.
///
/// Setting [constraintsTransform] to this allows [child] to render at least
/// its "natural" size, and grow along an axis if the incoming
/// [BoxConstraints] has a larger minimum constraint on that axis.
static BoxConstraints maxUnconstrained(BoxConstraints constraints) => constraints.copyWith(maxWidth: double.infinity, maxHeight: double.infinity);
static final Map<BoxConstraintsTransform, String> _debugKnownTransforms = <BoxConstraintsTransform, String>{
unmodified: 'unmodified',
unconstrained: 'unconstrained',
widthUnconstrained: 'width constraints removed',
heightUnconstrained: 'height constraints removed',
maxWidthUnconstrained: 'maxWidth constraint removed',
maxHeightUnconstrained: 'maxHeight constraint removed',
maxUnconstrained: 'maxWidth & maxHeight constraints removed',
};
/// The text direction to use when interpreting the [alignment] if it is an
/// [AlignmentDirectional].
///
/// Defaults to null, in which case [Directionality.maybeOf] is used to determine
/// the text direction.
final TextDirection? textDirection;
/// The alignment to use when laying out the child, if it has a different size
/// than this widget.
///
/// If this is an [AlignmentDirectional], then [textDirection] must not be
/// null.
///
/// See also:
///
/// * [Alignment] for non-[Directionality]-aware alignments.
/// * [AlignmentDirectional] for [Directionality]-aware alignments.
final AlignmentGeometry alignment;
/// {@template flutter.widgets.constraintsTransform}
/// The function used to transform the incoming [BoxConstraints], to size
/// [child].
///
/// The function must return a [BoxConstraints] that is
/// [BoxConstraints.isNormalized].
///
/// See [ConstraintsTransformBox] for predefined common
/// [BoxConstraintsTransform]s.
/// {@endtemplate}
final BoxConstraintsTransform constraintsTransform;
/// {@macro flutter.material.Material.clipBehavior}
///
/// {@template flutter.widgets.ConstraintsTransformBox.clipBehavior}
/// In debug mode, if [clipBehavior] is [Clip.none], and the child overflows
/// its constraints, a warning will be printed on the console, and black and
/// yellow striped areas will appear where the overflow occurs. For other
/// values of [clipBehavior], the contents are clipped accordingly.
/// {@endtemplate}
///
/// Defaults to [Clip.none].
final Clip clipBehavior;
final String _debugTransformLabel;
@override
RenderConstraintsTransformBox createRenderObject(BuildContext context) {
return RenderConstraintsTransformBox(
textDirection: textDirection ?? Directionality.maybeOf(context),
alignment: alignment,
constraintsTransform: constraintsTransform,
clipBehavior: clipBehavior,
);
}
@override
void updateRenderObject(BuildContext context, covariant RenderConstraintsTransformBox renderObject) {
renderObject
..textDirection = textDirection ?? Directionality.maybeOf(context)
..constraintsTransform = constraintsTransform
..alignment = alignment
..clipBehavior = clipBehavior;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
final String? debugTransformLabel = _debugTransformLabel.isNotEmpty
? _debugTransformLabel
: _debugKnownTransforms[constraintsTransform];
if (debugTransformLabel != null) {
properties.add(DiagnosticsProperty<String>('constraints transform', debugTransformLabel));
}
}
}
/// A widget that imposes no constraints on its child, allowing it to render
/// at its "natural" size.
///
/// This allows a child to render at the size it would render if it were alone
/// on an infinite canvas with no constraints. This container will then attempt
/// to adopt the same size, within the limits of its own constraints. If it ends
/// up with a different size, it will align the child based on [alignment].
/// If the box cannot expand enough to accommodate the entire child, the
/// child will be clipped.
///
/// In debug mode, if the child overflows the container, a warning will be
/// printed on the console, and black and yellow striped areas will appear where
/// the overflow occurs.
///
/// See also:
///
/// * [ConstrainedBox], for a box which imposes constraints on its child.
/// * [Align], which loosens the constraints given to the child rather than
/// removing them entirely.
/// * [Container], a convenience widget that combines common painting,
/// positioning, and sizing widgets.
/// * [OverflowBox], a widget that imposes different constraints on its child
/// than it gets from its parent, possibly allowing the child to overflow
/// the parent.
/// * [ConstraintsTransformBox], a widget that sizes its child using a
/// transformed [BoxConstraints], and shows a warning if the child overflows
/// in debug mode.
class UnconstrainedBox extends StatelessWidget {
/// Creates a widget that imposes no constraints on its child, allowing it to
/// render at its "natural" size. If the child overflows the parents
/// constraints, a warning will be given in debug mode.
const UnconstrainedBox({
super.key,
this.child,
this.textDirection,
this.alignment = Alignment.center,
this.constrainedAxis,
this.clipBehavior = Clip.none,
}) : assert(alignment != null),
assert(clipBehavior != null);
/// The text direction to use when interpreting the [alignment] if it is an
/// [AlignmentDirectional].
final TextDirection? textDirection;
/// The alignment to use when laying out the child.
///
/// If this is an [AlignmentDirectional], then [textDirection] must not be
/// null.
///
/// See also:
///
/// * [Alignment] for non-[Directionality]-aware alignments.
/// * [AlignmentDirectional] for [Directionality]-aware alignments.
final AlignmentGeometry alignment;
/// The axis to retain constraints on, if any.
///
/// If not set, or set to null (the default), neither axis will retain its
/// constraints. If set to [Axis.vertical], then vertical constraints will
/// be retained, and if set to [Axis.horizontal], then horizontal constraints
/// will be retained.
final Axis? constrainedAxis;
/// {@macro flutter.material.Material.clipBehavior}
///
/// Defaults to [Clip.none].
final Clip clipBehavior;
/// The widget below this widget in the tree.
///
/// {@macro flutter.widgets.ProxyWidget.child}
final Widget? child;
BoxConstraintsTransform _axisToTransform(Axis? constrainedAxis) {
if (constrainedAxis != null) {
switch (constrainedAxis) {
case Axis.horizontal:
return ConstraintsTransformBox.heightUnconstrained;
case Axis.vertical:
return ConstraintsTransformBox.widthUnconstrained;
}
} else {
return ConstraintsTransformBox.unconstrained;
}
}
@override
Widget build(BuildContext context) {
return ConstraintsTransformBox(
textDirection: textDirection,
alignment: alignment,
clipBehavior: clipBehavior,
constraintsTransform: _axisToTransform(constrainedAxis),
child: child,
);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
properties.add(EnumProperty<Axis>('constrainedAxis', constrainedAxis, defaultValue: null));
properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
}
}
/// A widget that sizes its child to a fraction of the total available space.
/// For more details about the layout algorithm, see
/// [RenderFractionallySizedOverflowBox].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=PEsY654EGZ0}
///
/// {@tool dartpad}
/// This sample shows a [FractionallySizedBox] whose one child is 50% of
/// the box's size per the width and height factor parameters, and centered
/// within that box by the alignment parameter.
///
/// ** See code in examples/api/lib/widgets/basic/fractionally_sized_box.0.dart **
/// {@end-tool}
///
/// See also:
///
/// * [Align], which sizes itself based on its child's size and positions
/// the child according to an [Alignment] value.
/// * [OverflowBox], a widget that imposes different constraints on its child
/// than it gets from its parent, possibly allowing the child to overflow the
/// parent.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class FractionallySizedBox extends SingleChildRenderObjectWidget {
/// Creates a widget that sizes its child to a fraction of the total available space.
///
/// If non-null, the [widthFactor] and [heightFactor] arguments must be
/// non-negative.
const FractionallySizedBox({
super.key,
this.alignment = Alignment.center,
this.widthFactor,
this.heightFactor,
super.child,
}) : assert(alignment != null),
assert(widthFactor == null || widthFactor >= 0.0),
assert(heightFactor == null || heightFactor >= 0.0);
/// {@template flutter.widgets.basic.fractionallySizedBox.widthFactor}
/// If non-null, the fraction of the incoming width given to the child.
///
/// If non-null, the child is given a tight width constraint that is the max
/// incoming width constraint multiplied by this factor.
///
/// If null, the incoming width constraints are passed to the child
/// unmodified.
/// {@endtemplate}
final double? widthFactor;
/// {@template flutter.widgets.basic.fractionallySizedBox.heightFactor}
/// If non-null, the fraction of the incoming height given to the child.
///
/// If non-null, the child is given a tight height constraint that is the max
/// incoming height constraint multiplied by this factor.
///
/// If null, the incoming height constraints are passed to the child
/// unmodified.
/// {@endtemplate}
final double? heightFactor;
/// {@template flutter.widgets.basic.fractionallySizedBox.alignment}
/// How to align the child.
///
/// The x and y values of the alignment control the horizontal and vertical
/// alignment, respectively. An x value of -1.0 means that the left edge of
/// the child is aligned with the left edge of the parent whereas an x value
/// of 1.0 means that the right edge of the child is aligned with the right
/// edge of the parent. Other values interpolate (and extrapolate) linearly.
/// For example, a value of 0.0 means that the center of the child is aligned
/// with the center of the parent.
///
/// Defaults to [Alignment.center].
///
/// See also:
///
/// * [Alignment], a class with convenient constants typically used to
/// specify an [AlignmentGeometry].
/// * [AlignmentDirectional], like [Alignment] for specifying alignments
/// relative to text direction.
/// {@endtemplate}
final AlignmentGeometry alignment;
@override
RenderFractionallySizedOverflowBox createRenderObject(BuildContext context) {
return RenderFractionallySizedOverflowBox(
alignment: alignment,
widthFactor: widthFactor,
heightFactor: heightFactor,
textDirection: Directionality.maybeOf(context),
);
}
@override
void updateRenderObject(BuildContext context, RenderFractionallySizedOverflowBox renderObject) {
renderObject
..alignment = alignment
..widthFactor = widthFactor
..heightFactor = heightFactor
..textDirection = Directionality.maybeOf(context);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
properties.add(DoubleProperty('widthFactor', widthFactor, defaultValue: null));
properties.add(DoubleProperty('heightFactor', heightFactor, defaultValue: null));
}
}
/// A box that limits its size only when it's unconstrained.
///
/// If this widget's maximum width is unconstrained then its child's width is
/// limited to [maxWidth]. Similarly, if this widget's maximum height is
/// unconstrained then its child's height is limited to [maxHeight].
///
/// This has the effect of giving the child a natural dimension in unbounded
/// environments. For example, by providing a [maxHeight] to a widget that
/// normally tries to be as big as possible, the widget will normally size
/// itself to fit its parent, but when placed in a vertical list, it will take
/// on the given height.
///
/// This is useful when composing widgets that normally try to match their
/// parents' size, so that they behave reasonably in lists (which are
/// unbounded).
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=uVki2CIzBTs}
///
/// See also:
///
/// * [ConstrainedBox], which applies its constraints in all cases, not just
/// when the incoming constraints are unbounded.
/// * [SizedBox], which lets you specify tight constraints by explicitly
/// specifying the height or width.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class LimitedBox extends SingleChildRenderObjectWidget {
/// Creates a box that limits its size only when it's unconstrained.
///
/// The [maxWidth] and [maxHeight] arguments must not be null and must not be
/// negative.
const LimitedBox({
super.key,
this.maxWidth = double.infinity,
this.maxHeight = double.infinity,
super.child,
}) : assert(maxWidth != null && maxWidth >= 0.0),
assert(maxHeight != null && maxHeight >= 0.0);
/// The maximum width limit to apply in the absence of a
/// [BoxConstraints.maxWidth] constraint.
final double maxWidth;
/// The maximum height limit to apply in the absence of a
/// [BoxConstraints.maxHeight] constraint.
final double maxHeight;
@override
RenderLimitedBox createRenderObject(BuildContext context) {
return RenderLimitedBox(
maxWidth: maxWidth,
maxHeight: maxHeight,
);
}
@override
void updateRenderObject(BuildContext context, RenderLimitedBox renderObject) {
renderObject
..maxWidth = maxWidth
..maxHeight = maxHeight;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DoubleProperty('maxWidth', maxWidth, defaultValue: double.infinity));
properties.add(DoubleProperty('maxHeight', maxHeight, defaultValue: double.infinity));
}
}
/// A widget that imposes different constraints on its child than it gets
/// from its parent, possibly allowing the child to overflow the parent.
///
/// See also:
///
/// * [RenderConstrainedOverflowBox] for details about how [OverflowBox] is
/// rendered.
/// * [SizedOverflowBox], a widget that is a specific size but passes its
/// original constraints through to its child, which may then overflow.
/// * [ConstrainedBox], a widget that imposes additional constraints on its
/// child.
/// * [UnconstrainedBox], a container that tries to let its child draw without
/// constraints.
/// * [SizedBox], a box with a specified size.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class OverflowBox extends SingleChildRenderObjectWidget {
/// Creates a widget that lets its child overflow itself.
const OverflowBox({
super.key,
this.alignment = Alignment.center,
this.minWidth,
this.maxWidth,
this.minHeight,
this.maxHeight,
super.child,
});
/// How to align the child.
///
/// The x and y values of the alignment control the horizontal and vertical
/// alignment, respectively. An x value of -1.0 means that the left edge of
/// the child is aligned with the left edge of the parent whereas an x value
/// of 1.0 means that the right edge of the child is aligned with the right
/// edge of the parent. Other values interpolate (and extrapolate) linearly.
/// For example, a value of 0.0 means that the center of the child is aligned
/// with the center of the parent.
///
/// Defaults to [Alignment.center].
///
/// See also:
///
/// * [Alignment], a class with convenient constants typically used to
/// specify an [AlignmentGeometry].
/// * [AlignmentDirectional], like [Alignment] for specifying alignments
/// relative to text direction.
final AlignmentGeometry alignment;
/// The minimum width constraint to give the child. Set this to null (the
/// default) to use the constraint from the parent instead.
final double? minWidth;
/// The maximum width constraint to give the child. Set this to null (the
/// default) to use the constraint from the parent instead.
final double? maxWidth;
/// The minimum height constraint to give the child. Set this to null (the
/// default) to use the constraint from the parent instead.
final double? minHeight;
/// The maximum height constraint to give the child. Set this to null (the
/// default) to use the constraint from the parent instead.
final double? maxHeight;
@override
RenderConstrainedOverflowBox createRenderObject(BuildContext context) {
return RenderConstrainedOverflowBox(
alignment: alignment,
minWidth: minWidth,
maxWidth: maxWidth,
minHeight: minHeight,
maxHeight: maxHeight,
textDirection: Directionality.maybeOf(context),
);
}
@override
void updateRenderObject(BuildContext context, RenderConstrainedOverflowBox renderObject) {
renderObject
..alignment = alignment
..minWidth = minWidth
..maxWidth = maxWidth
..minHeight = minHeight
..maxHeight = maxHeight
..textDirection = Directionality.maybeOf(context);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
properties.add(DoubleProperty('minWidth', minWidth, defaultValue: null));
properties.add(DoubleProperty('maxWidth', maxWidth, defaultValue: null));
properties.add(DoubleProperty('minHeight', minHeight, defaultValue: null));
properties.add(DoubleProperty('maxHeight', maxHeight, defaultValue: null));
}
}
/// A widget that is a specific size but passes its original constraints
/// through to its child, which may then overflow.
///
/// See also:
///
/// * [OverflowBox], A widget that imposes different constraints on its child
/// than it gets from its parent, possibly allowing the child to overflow the
/// parent.
/// * [ConstrainedBox], a widget that imposes additional constraints on its
/// child.
/// * [UnconstrainedBox], a container that tries to let its child draw without
/// constraints.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class SizedOverflowBox extends SingleChildRenderObjectWidget {
/// Creates a widget of a given size that lets its child overflow.
///
/// The [size] argument must not be null.
const SizedOverflowBox({
super.key,
required this.size,
this.alignment = Alignment.center,
super.child,
}) : assert(size != null),
assert(alignment != null);
/// How to align the child.
///
/// The x and y values of the alignment control the horizontal and vertical
/// alignment, respectively. An x value of -1.0 means that the left edge of
/// the child is aligned with the left edge of the parent whereas an x value
/// of 1.0 means that the right edge of the child is aligned with the right
/// edge of the parent. Other values interpolate (and extrapolate) linearly.
/// For example, a value of 0.0 means that the center of the child is aligned
/// with the center of the parent.
///
/// Defaults to [Alignment.center].
///
/// See also:
///
/// * [Alignment], a class with convenient constants typically used to
/// specify an [AlignmentGeometry].
/// * [AlignmentDirectional], like [Alignment] for specifying alignments
/// relative to text direction.
final AlignmentGeometry alignment;
/// The size this widget should attempt to be.
final Size size;
@override
RenderSizedOverflowBox createRenderObject(BuildContext context) {
return RenderSizedOverflowBox(
alignment: alignment,
requestedSize: size,
textDirection: Directionality.of(context),
);
}
@override
void updateRenderObject(BuildContext context, RenderSizedOverflowBox renderObject) {
renderObject
..alignment = alignment
..requestedSize = size
..textDirection = Directionality.of(context);
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
properties.add(DiagnosticsProperty<Size>('size', size, defaultValue: null));
}
}
/// A widget that lays the child out as if it was in the tree, but without
/// painting anything, without making the child available for hit testing, and
/// without taking any room in the parent.
///
/// Offstage children are still active: they can receive focus and have keyboard
/// input directed to them.
///
/// Animations continue to run in offstage children, and therefore use battery
/// and CPU time, regardless of whether the animations end up being visible.
///
/// [Offstage] can be used to measure the dimensions of a widget without
/// bringing it on screen (yet). To hide a widget from view while it is not
/// needed, prefer removing the widget from the tree entirely rather than
/// keeping it alive in an [Offstage] subtree.
///
/// {@tool dartpad}
/// This example shows a [FlutterLogo] widget when the `_offstage` member field
/// is false, and hides it without any room in the parent when it is true. When
/// offstage, this app displays a button to get the logo size, which will be
/// displayed in a [SnackBar].
///
/// ** See code in examples/api/lib/widgets/basic/offstage.0.dart **
/// {@end-tool}
///
/// See also:
///
/// * [Visibility], which can hide a child more efficiently (albeit less
/// subtly).
/// * [TickerMode], which can be used to disable animations in a subtree.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class Offstage extends SingleChildRenderObjectWidget {
/// Creates a widget that visually hides its child.
const Offstage({ super.key, this.offstage = true, super.child })
: assert(offstage != null);
/// Whether the child is hidden from the rest of the tree.
///
/// If true, the child is laid out as if it was in the tree, but without
/// painting anything, without making the child available for hit testing, and
/// without taking any room in the parent.
///
/// Offstage children are still active: they can receive focus and have keyboard
/// input directed to them.
///
/// Animations continue to run in offstage children, and therefore use battery
/// and CPU time, regardless of whether the animations end up being visible.
///
/// If false, the child is included in the tree as normal.
final bool offstage;
@override
RenderOffstage createRenderObject(BuildContext context) => RenderOffstage(offstage: offstage);
@override
void updateRenderObject(BuildContext context, RenderOffstage renderObject) {
renderObject.offstage = offstage;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DiagnosticsProperty<bool>('offstage', offstage));
}
@override
SingleChildRenderObjectElement createElement() => _OffstageElement(this);
}
class _OffstageElement extends SingleChildRenderObjectElement {
_OffstageElement(Offstage super.widget);
@override
void debugVisitOnstageChildren(ElementVisitor visitor) {
if (!(widget as Offstage).offstage) {
super.debugVisitOnstageChildren(visitor);
}
}
}
/// A widget that attempts to size the child to a specific aspect ratio.
///
/// The widget first tries the largest width permitted by the layout
/// constraints. The height of the widget is determined by applying the
/// given aspect ratio to the width, expressed as a ratio of width to height.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=XcnP3_mO_Ms}
///
/// For example, a 16:9 width:height aspect ratio would have a value of
/// 16.0/9.0. If the maximum width is infinite, the initial width is determined
/// by applying the aspect ratio to the maximum height.
///
/// {@tool dartpad}
/// This examples shows how AspectRatio sets width when its parent's width
/// constraint is infinite. Since its parent's allowed height is a fixed value,
/// the actual width is determined via the given AspectRatio.
///
/// Since the height is fixed at 100.0 in this example and the aspect ratio is
/// set to 16 / 9, the width should then be 100.0 / 9 * 16.
///
/// ** See code in examples/api/lib/widgets/basic/aspect_ratio.0.dart **
/// {@end-tool}
///
/// Now consider a second example, this time with an aspect ratio of 2.0 and
/// layout constraints that require the width to be between 0.0 and 100.0 and
/// the height to be between 0.0 and 100.0. We'll select a width of 100.0 (the
/// biggest allowed) and a height of 50.0 (to match the aspect ratio).
///
/// {@tool dartpad}
///
///
/// ** See code in examples/api/lib/widgets/basic/aspect_ratio.1.dart **
/// {@end-tool}
///
/// In that same situation, if the aspect ratio is 0.5, we'll also select a
/// width of 100.0 (still the biggest allowed) and we'll attempt to use a height
/// of 200.0. Unfortunately, that violates the constraints because the child can
/// be at most 100.0 pixels tall. The widget will then take that value
/// and apply the aspect ratio again to obtain a width of 50.0. That width is
/// permitted by the constraints and the child receives a width of 50.0 and a
/// height of 100.0. If the width were not permitted, the widget would
/// continue iterating through the constraints. If the widget does not
/// find a feasible size after consulting each constraint, the widget
/// will eventually select a size for the child that meets the layout
/// constraints but fails to meet the aspect ratio constraints.
///
/// {@tool dartpad}
///
///
/// ** See code in examples/api/lib/widgets/basic/aspect_ratio.2.dart **
/// {@end-tool}
///
/// See also:
///
/// * [Align], a widget that aligns its child within itself and optionally
/// sizes itself based on the child's size.
/// * [ConstrainedBox], a widget that imposes additional constraints on its
/// child.
/// * [UnconstrainedBox], a container that tries to let its child draw without
/// constraints.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class AspectRatio extends SingleChildRenderObjectWidget {
/// Creates a widget with a specific aspect ratio.
///
/// The [aspectRatio] argument must be a finite number greater than zero.
const AspectRatio({
super.key,
required this.aspectRatio,
super.child,
}) : assert(aspectRatio != null),
assert(aspectRatio > 0.0);
/// The aspect ratio to attempt to use.
///
/// The aspect ratio is expressed as a ratio of width to height. For example,
/// a 16:9 width:height aspect ratio would have a value of 16.0/9.0.
final double aspectRatio;
@override
RenderAspectRatio createRenderObject(BuildContext context) => RenderAspectRatio(aspectRatio: aspectRatio);
@override
void updateRenderObject(BuildContext context, RenderAspectRatio renderObject) {
renderObject.aspectRatio = aspectRatio;
}
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(DoubleProperty('aspectRatio', aspectRatio));
}
}
/// A widget that sizes its child to the child's maximum intrinsic width.
///
/// This class is useful, for example, when unlimited width is available and
/// you would like a child that would otherwise attempt to expand infinitely to
/// instead size itself to a more reasonable width.
///
/// The constraints that this widget passes to its child will adhere to the
/// parent's constraints, so if the constraints are not large enough to satisfy
/// the child's maximum intrinsic width, then the child will get less width
/// than it otherwise would. Likewise, if the minimum width constraint is
/// larger than the child's maximum intrinsic width, the child will be given
/// more width than it otherwise would.
///
/// If [stepWidth] is non-null, the child's width will be snapped to a multiple
/// of the [stepWidth]. Similarly, if [stepHeight] is non-null, the child's
/// height will be snapped to a multiple of the [stepHeight].
///
/// This class is relatively expensive, because it adds a speculative layout
/// pass before the final layout phase. Avoid using it where possible. In the
/// worst case, this widget can result in a layout that is O(N²) in the depth of
/// the tree.
///
/// See also:
///
/// * [Align], a widget that aligns its child within itself. This can be used
/// to loosen the constraints passed to the [RenderIntrinsicWidth],
/// allowing the [RenderIntrinsicWidth]'s child to be smaller than that of
/// its parent.
/// * [Row], which when used with [CrossAxisAlignment.stretch] can be used
/// to loosen just the width constraints that are passed to the
/// [RenderIntrinsicWidth], allowing the [RenderIntrinsicWidth]'s child's
/// width to be smaller than that of its parent.
/// * [The catalog of layout widgets](https://flutter.dev/widgets/layout/).
class IntrinsicWidth extends SingleChildRenderObjectWidget {
/// Creates a widget that sizes its child to the child's intrinsic width.
///
/// This class is relatively expensive. Avoid using it where possible.
const IntrinsicWidth({ super.key, this.stepWidth, this.stepHeight, super.child })
: assert(stepWidth == null || stepWidth >= 0.0),
assert(stepHeight == null || stepHeight >= 0.0);
/// If non-null, force the child's width to be a multiple of this value.
///
/// If null or 0.0 the child's width will be the same as its maximum
/// intrinsic width.
///
/// This value must not be negative.
///
/// See also:
///
/// * [RenderBox.getMaxIntrinsicWidth], which defines a widget's max
/// intrinsic width in general.
final double? stepWidth;
/// If non-null, force the child's height to be a multiple of this value.
///
/// If null or 0.0 the child's height will not be constrained.
///
/// This value must not be negative.
final double? stepHeight;
double? get _stepWidth => stepWidth == 0.0 ? null : stepWidth;
double? get _stepHeight => stepHeight == 0.0 ? null : stepHeight;
@override
RenderIntrinsicWidth createRenderObject(BuildContext context) {
return RenderIntrinsicWidth(stepWidth: _stepWidth, stepHeight: _stepHeight);
}
@override
void updateRenderObject(BuildContext context, RenderIntrinsicWidth renderObject) {
renderObject
..stepWidth = _stepWidth
..stepHeight = _stepHeight;
}
}
/// A widget that sizes its child to the child's intrinsic height.
///
/// This class is useful, for example, when unlimited height is available and
/// you would like a child that would otherwise attempt to expand infinitely to
/// instead size itself to a more reasonable height.
///
/// The constraints that this widget passes to its child will adhere to the
/// parent's constraints, so if the constraints are not large enough to satisfy
/// the child's maximum intrinsic height, then the child will get less height
/// than it otherwise would. Likewise, if the minimum height constraint is
/// larger than the child's maximum intrinsic height, the child will be given
/// more height than it otherwise would.
///
/// This class is relatively expensive, because it adds a speculative layout
/// pass before the final layout phase. Avoid using it where possible. In the
/// worst case, this widget can result in a layout that is O(N²) in the depth of
/// the tree.
///
/// See also:
///
/// * [Align], a widget that aligns its child within itself. This can be used
/// to loosen the constraints passed to the [RenderIntrinsicHeight],
/// allowing the [RenderIntrinsicHeight]'s child to be smaller than that of
/// its parent.
/// * [Column], which when used with [CrossAxisAlignment.stretch] can be used
/// to loosen just the height constraints that are passed to the
/// [RenderIntrinsicHeight], allowing the [RenderIntrinsicHeight]'s child's
/// height to be smaller than that of its parent.
/// * [The catalog of layout widgets](https://flutter.dev/widgets/layout/).
class IntrinsicHeight extends SingleChildRenderObjectWidget {
/// Creates a widget that sizes its child to the child's intrinsic height.
///
/// This class is relatively expensive. Avoid using it where possible.
const IntrinsicHeight({ super.key, super.child });
@override
RenderIntrinsicHeight createRenderObject(BuildContext context) => RenderIntrinsicHeight();
}
/// A widget that positions its child according to the child's baseline.
///
/// This widget shifts the child down such that the child's baseline (or the
/// bottom of the child, if the child has no baseline) is [baseline]
/// logical pixels below the top of this box, then sizes this box to
/// contain the child. If [baseline] is less than the distance from
/// the top of the child to the baseline of the child, then the child
/// is top-aligned instead.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=8ZaFk0yvNlI}
///
/// See also:
///
/// * [Align], a widget that aligns its child within itself and optionally
/// sizes itself based on the child's size.
/// * [Center], a widget that centers its child within itself.
/// * The [catalog of layout widgets](https://flutter.dev/widgets/layout/).
class Baseline extends SingleChildRenderObjectWidget {
/// Creates a widget that positions its child according to the child's baseline.
///
/// The [baseline] and [baselineType] arguments must not be null.
const Baseline({
super.key,
required this.baseline,
required this.baselineType,
super.child,
}) : assert(baseline != null),
assert(baselineType != null);
/// The number of logical pixels from the top of this box at which to position
/// the child's baseline.
final double baseline;
/// The type of baseline to use for positioning the child.
final TextBaseline baselineType;
@override
RenderBaseline createRenderObject(BuildContext context) {
return RenderBaseline(baseline: baseline, baselineType: baselineType);
}
@override
void updateRenderObject(BuildContext context, RenderBaseline renderObject) {
renderObject
..baseline = baseline
..baselineType = baselineType;
}
}
// SLIVERS
/// A sliver that contains a single box widget.
///
/// Slivers are special-purpose widgets that can be combined using a
/// [CustomScrollView] to create custom scroll effects. A [SliverToBoxAdapter]
/// is a basic sliver that creates a bridge back to one of the usual box-based
/// widgets.
///
/// Rather than using multiple [SliverToBoxAdapter] widgets to display multiple
/// box widgets in a [CustomScrollView], consider using [SliverList],
/// [SliverFixedExtentList], [SliverPrototypeExtentList], or [SliverGrid],
/// which are more efficient because they instantiate only those children that
/// are actually visible through the scroll view's viewport.
///
/// See also:
///