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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 'package:flutter/rendering.dart';
import 'basic.dart';
import 'framework.dart';
/// An interface for widgets that can return the size this widget would prefer
/// if it were otherwise unconstrained.
/// There are a few cases, notably [AppBar] and [TabBar], where it would be
/// undesirable for the widget to constrain its own size but where the widget
/// needs to expose a preferred or "default" size. For example a primary
/// [Scaffold] sets its app bar height to the app bar's preferred height
/// plus the height of the system status bar.
/// Widgets that need to know the preferred size of their child can require
/// that their child implement this interface by using this class rather
/// than [Widget] as the type of their `child` property.
/// Use [PreferredSize] to give a preferred size to an arbitrary widget.
// (We ignore `avoid_implementing_value_types` here because the superclass
// doesn't really implement `operator ==`, it just overrides it to _prevent_ it
// from being implemented, which is the exact opposite of the spirit of the
// `avoid_implementing_value_types` lint.)
// ignore: avoid_implementing_value_types
abstract class PreferredSizeWidget implements Widget {
/// The size this widget would prefer if it were otherwise unconstrained.
/// In many cases it's only necessary to define one preferred dimension.
/// For example the [Scaffold] only depends on its app bar's preferred
/// height. In that case implementations of this method can just return
/// `Size.fromHeight(myAppBarHeight)`.
Size get preferredSize;
/// A widget with a preferred size.
/// This widget does not impose any constraints on its child, and it doesn't
/// affect the child's layout in any way. It just advertises a preferred size
/// which can be used by the parent.
/// Parents like [Scaffold] use [PreferredSizeWidget] to require that their
/// children implement that interface. To give a preferred size to an arbitrary
/// widget so that it can be used in a `child` property of that type, this
/// widget, [PreferredSize], can be used.
/// Widgets like [AppBar] implement a [PreferredSizeWidget], so that this
/// [PreferredSize] widget is not necessary for them.
/// {@tool dartpad}
/// This sample shows a custom widget, similar to an [AppBar], which uses a
/// [PreferredSize] widget, with its height set to 80 logical pixels.
/// Changing the [PreferredSize] can be used to change the height
/// of the custom app bar.
/// ** See code in examples/api/lib/widgets/preferred_size/preferred_size.0.dart **
/// {@end-tool}
/// See also:
/// * [AppBar.bottom] and [Scaffold.appBar], which require preferred size widgets.
/// * [PreferredSizeWidget], the interface which this widget implements to expose
/// its preferred size.
/// * [AppBar] and [TabBar], which implement PreferredSizeWidget.
class PreferredSize extends StatelessWidget implements PreferredSizeWidget {
/// Creates a widget that has a preferred size that the parent can query.
const PreferredSize({
required this.child,
required this.preferredSize,
/// The widget below this widget in the tree.
/// {@macro flutter.widgets.ProxyWidget.child}
final Widget child;
final Size preferredSize;
Widget build(BuildContext context) => child;