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// Copyright 2016 The Chromium 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 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/scheduler.dart';
import 'box.dart';
import 'object.dart';
import 'shifted_box.dart';
/// A [RenderAnimatedSize] can be in exactly one of these states.
@visibleForTesting
enum RenderAnimatedSizeState {
/// The initial state, when we do not yet know what the starting and target
/// sizes are to animate.
///
/// The next state is [stable].
start,
/// At this state the child's size is assumed to be stable and we are either
/// animating, or waiting for the child's size to change.
///
/// If the child's size changes, the state will become [changed]. Otherwise,
/// it remains [stable].
stable,
/// At this state we know that the child has changed once after being assumed
/// [stable].
///
/// The next state will be one of:
///
/// * [stable] if the child's size stabilized immediately. This is a signal
/// for the render object to begin animating the size towards the child's new
/// size.
///
/// * [unstable] if the child's size continues to change.
changed,
/// At this state the child's size is assumed to be unstable (changing each
/// frame).
///
/// Instead of chasing the child's size in this state, the render object
/// tightly tracks the child's size until it stabilizes.
///
/// The render object remains in this state until a frame where the child's
/// size remains the same as the previous frame. At that time, the next state
/// is [stable].
unstable,
}
/// A render object that animates its size to its child's size over a given
/// [duration] and with a given [curve]. If the child's size itself animates
/// (i.e. if it changes size two frames in a row, as opposed to abruptly
/// changing size in one frame then remaining that size in subsequent frames),
/// this render object sizes itself to fit the child instead of animating
/// itself.
///
/// When the child overflows the current animated size of this render object, it
/// is clipped.
class RenderAnimatedSize extends RenderAligningShiftedBox {
/// Creates a render object that animates its size to match its child.
/// The [duration] and [curve] arguments define the animation.
///
/// The [alignment] argument is used to align the child when the parent is not
/// (yet) the same size as the child.
///
/// The [duration] is required.
///
/// The [vsync] should specify a [TickerProvider] for the animation
/// controller.
///
/// The arguments [duration], [curve], [alignment], and [vsync] must
/// not be null.
RenderAnimatedSize({
@required TickerProvider vsync,
@required Duration duration,
Curve curve: Curves.linear,
AlignmentGeometry alignment: Alignment.center,
TextDirection textDirection,
RenderBox child,
}) : assert(vsync != null),
assert(duration != null),
assert(curve != null),
_vsync = vsync,
super(child: child, alignment: alignment, textDirection: textDirection) {
_controller = new AnimationController(
vsync: vsync,
duration: duration,
)..addListener(() {
if (_controller.value != _lastValue)
markNeedsLayout();
});
_animation = new CurvedAnimation(
parent: _controller,
curve: curve
);
}
AnimationController _controller;
CurvedAnimation _animation;
final SizeTween _sizeTween = new SizeTween();
bool _hasVisualOverflow;
double _lastValue;
/// The state this size animation is in.
///
/// See [RenderAnimatedSizeState] for possible states.
@visibleForTesting
RenderAnimatedSizeState get state => _state;
RenderAnimatedSizeState _state = RenderAnimatedSizeState.start;
/// The duration of the animation.
Duration get duration => _controller.duration;
set duration(Duration value) {
assert(value != null);
if (value == _controller.duration)
return;
_controller.duration = value;
}
/// The curve of the animation.
Curve get curve => _animation.curve;
set curve(Curve value) {
assert(value != null);
if (value == _animation.curve)
return;
_animation.curve = value;
}
/// Whether the size is being currently animated towards the child's size.
///
/// See [RenderAnimatedSizeState] for situations when we may not be animating
/// the size.
bool get isAnimating => _controller.isAnimating;
/// The [TickerProvider] for the [AnimationController] that runs the animation.
TickerProvider get vsync => _vsync;
TickerProvider _vsync;
set vsync(TickerProvider value) {
assert(value != null);
if (value == _vsync)
return;
_vsync = value;
_controller.resync(vsync);
}
@override
void detach() {
_controller.stop();
super.detach();
}
Size get _animatedSize {
return _sizeTween.evaluate(_animation);
}
@override
void performLayout() {
_lastValue = _controller.value;
_hasVisualOverflow = false;
if (child == null || constraints.isTight) {
_controller.stop();
size = _sizeTween.begin = _sizeTween.end = constraints.smallest;
_state = RenderAnimatedSizeState.start;
child?.layout(constraints);
return;
}
child.layout(constraints, parentUsesSize: true);
assert(_state != null);
switch (_state) {
case RenderAnimatedSizeState.start:
_layoutStart();
break;
case RenderAnimatedSizeState.stable:
_layoutStable();
break;
case RenderAnimatedSizeState.changed:
_layoutChanged();
break;
case RenderAnimatedSizeState.unstable:
_layoutUnstable();
break;
}
size = constraints.constrain(_animatedSize);
alignChild();
if (size.width < _sizeTween.end.width ||
size.height < _sizeTween.end.height)
_hasVisualOverflow = true;
}
void _restartAnimation() {
_lastValue = 0.0;
_controller.forward(from: 0.0);
}
/// Laying out the child for the first time.
///
/// We have the initial size to animate from, but we do not have the target
/// size to animate to, so we set both ends to child's size.
void _layoutStart() {
_sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
_state = RenderAnimatedSizeState.stable;
}
/// At this state we're assuming the child size is stable and letting the
/// animation run its course.
///
/// If during animation the size of the child changes we restart the
/// animation.
void _layoutStable() {
if (_sizeTween.end != child.size) {
_sizeTween.begin = size;
_sizeTween.end = debugAdoptSize(child.size);
_restartAnimation();
_state = RenderAnimatedSizeState.changed;
} else if (_controller.value == _controller.upperBound) {
// Animation finished. Reset target sizes.
_sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
} else if (!_controller.isAnimating) {
_controller.forward(); // resume the animation after being detached
}
}
/// This state indicates that the size of the child changed once after being
/// considered stable.
///
/// If the child stabilizes immediately, we go back to stable state. If it
/// changes again, we match the child's size, restart animation and go to
/// unstable state.
void _layoutChanged() {
if (_sizeTween.end != child.size) {
// Child size changed again. Match the child's size and restart animation.
_sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
_restartAnimation();
_state = RenderAnimatedSizeState.unstable;
} else {
// Child size stabilized.
_state = RenderAnimatedSizeState.stable;
if (!_controller.isAnimating)
_controller.forward(); // resume the animation after being detached
}
}
/// The child's size is not stable.
///
/// Continue tracking the child's size until is stabilizes.
void _layoutUnstable() {
if (_sizeTween.end != child.size) {
// Still unstable. Continue tracking the child.
_sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
_restartAnimation();
} else {
// Child size stabilized.
_controller.stop();
_state = RenderAnimatedSizeState.stable;
}
}
@override
void paint(PaintingContext context, Offset offset) {
if (child != null && _hasVisualOverflow) {
final Rect rect = Offset.zero & size;
context.pushClipRect(needsCompositing, offset, rect, super.paint);
} else {
super.paint(context, offset);
}
}
}