packages/flutter/lib/src/material/banner.dart - mirrors/flutter - Git at Google

 // 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/widgets.dart';

 import 'banner_theme.dart';
 import 'divider.dart';
 import 'material.dart';
 import 'scaffold.dart';
 import 'theme.dart';

 // Examples can assume:
 // late BuildContext context;

 const Duration _materialBannerTransitionDuration = Duration(milliseconds: 250);
 const Curve _materialBannerHeightCurve = Curves.fastOutSlowIn;

 /// Specify how a [MaterialBanner] was closed.
 ///
 /// The [ScaffoldMessengerState.showMaterialBanner] function returns a
 /// [ScaffoldFeatureController]. The value of the controller's closed property
 /// is a Future that resolves to a MaterialBannerClosedReason. Applications that need
 /// to know how a [MaterialBanner] was closed can use this value.
 ///
 /// Example:
 ///
 /// ```dart
 /// ScaffoldMessenger.of(context).showMaterialBanner(
 ///   const MaterialBanner(
 ///     content: Text('Message...'),
 ///     actions: <Widget>[
 ///       // ...
 ///     ],
 ///   )
 /// ).closed.then((MaterialBannerClosedReason reason) {
 ///    // ...
 /// });
 /// ```
 enum MaterialBannerClosedReason {
   /// The material banner was closed through a [SemanticsAction.dismiss].
   dismiss,

   /// The material banner was closed by a user's swipe.
   swipe,

   /// The material banner was closed by the [ScaffoldFeatureController] close callback
   /// or by calling [ScaffoldMessengerState.hideCurrentMaterialBanner] directly.
   hide,

   /// The material banner was closed by a call to [ScaffoldMessengerState.removeCurrentMaterialBanner].
   remove,
 }

 /// A Material Design banner.
 ///
 /// A banner displays an important, succinct message, and provides actions for
 /// users to address (or dismiss the banner). A user action is required for it
 /// to be dismissed.
 ///
 /// Banners should be displayed at the top of the screen, below a top app bar.
 /// They are persistent and non-modal, allowing the user to either ignore them or
 /// interact with them at any time.
 ///
 /// {@tool dartpad}
 /// Banners placed directly into the widget tree are static.
 ///
 /// ** See code in examples/api/lib/material/banner/material_banner.0.dart **
 /// {@end-tool}
 ///
 /// {@tool dartpad}
 /// MaterialBanner's can also be presented through a [ScaffoldMessenger].
 /// Here is an example where ScaffoldMessengerState.showMaterialBanner() is used to show the MaterialBanner.
 ///
 /// ** See code in examples/api/lib/material/banner/material_banner.1.dart **
 /// {@end-tool}
 ///
 /// The [actions] will be placed beside the [content] if there is only one.
 /// Otherwise, the [actions] will be placed below the [content]. Use
 /// [forceActionsBelow] to override this behavior.
 ///
 /// If the [actions] placed below the [content], they will be laid out in a row.
 /// If there isn't sufficient room to display everything, they are laid out
 /// in a column instead.
 ///
 /// The [actions] and [content] must be provided. An optional leading widget
 /// (typically an [Image]) can also be provided. The [contentTextStyle] and
 /// [backgroundColor] can be provided to customize the banner.
 ///
 /// This widget is unrelated to the widgets library [Banner] widget.
 class MaterialBanner extends StatefulWidget {
   /// Creates a [MaterialBanner].
   ///
   /// The [actions], [content], and [forceActionsBelow] must be non-null.
   /// The [actions].length must be greater than 0. The [elevation] must be null or
   /// non-negative.
   const MaterialBanner({
     super.key,
     required this.content,
     this.contentTextStyle,
     required this.actions,
     this.elevation,
     this.leading,
     this.backgroundColor,
     this.surfaceTintColor,
     this.shadowColor,
     this.dividerColor,
     this.padding,
     this.margin,
     this.leadingPadding,
     this.forceActionsBelow = false,
     this.overflowAlignment = OverflowBarAlignment.end,
     this.animation,
     this.onVisible,
   }) : assert(elevation == null || elevation >= 0.0);

   /// The content of the [MaterialBanner].
   ///
   /// Typically a [Text] widget.
   final Widget content;

   /// Style for the text in the [content] of the [MaterialBanner].
   ///
   /// If `null`, [MaterialBannerThemeData.contentTextStyle] is used. If that is
   /// also `null`, [TextTheme.bodyMedium] of [ThemeData.textTheme] is used.
   final TextStyle? contentTextStyle;

   /// The set of actions that are displayed at the bottom or trailing side of
   /// the [MaterialBanner].
   ///
   /// Typically this is a list of [TextButton] widgets.
   final List<Widget> actions;

   /// The z-coordinate at which to place the material banner.
   ///
   /// This controls the size of the shadow below the material banner.
   ///
   /// Defines the banner's [Material.elevation].
   ///
   /// If this property is null, then [MaterialBannerThemeData.elevation] of
   /// [ThemeData.bannerTheme] is used, if that is also null, the default value is 0.
   /// If the elevation is 0, the [Scaffold]'s body will be pushed down by the
   /// MaterialBanner when used with [ScaffoldMessenger].
   final double? elevation;

   /// The (optional) leading widget of the [MaterialBanner].
   ///
   /// Typically an [Icon] widget.
   final Widget? leading;

   /// The color of the surface of this [MaterialBanner].
   ///
   /// If `null`, [MaterialBannerThemeData.backgroundColor] is used. If that is
   /// also `null`, [ColorScheme.surface] of [ThemeData.colorScheme] is used.
   final Color? backgroundColor;

   /// The color used as an overlay on [backgroundColor] to indicate elevation.
   ///
   /// If null, [MaterialBannerThemeData.surfaceTintColor] is used. If that
   /// is also null, the default value is [ColorScheme.surfaceTint].
   ///
   /// See [Material.surfaceTintColor] for more details on how this
   /// overlay is applied.
   final Color? surfaceTintColor;

   /// The color of the shadow below the [MaterialBanner].
   ///
   /// If this property is null, then [MaterialBannerThemeData.shadowColor] of
   /// [ThemeData.bannerTheme] is used. If that is also null, the default value
   /// is null.
   final Color? shadowColor;

   /// The color of the divider.
   ///
   /// If this property is null, then [MaterialBannerThemeData.dividerColor] of
   /// [ThemeData.bannerTheme] is used. If that is also null, the default value
   /// is [ColorScheme.surfaceVariant].
   final Color? dividerColor;

   /// The amount of space by which to inset the [content].
   ///
   /// If the [actions] are below the [content], this defaults to
   /// `EdgeInsetsDirectional.only(start: 16.0, top: 24.0, end: 16.0, bottom: 4.0)`.
   ///
   /// If the [actions] are trailing the [content], this defaults to
   /// `EdgeInsetsDirectional.only(start: 16.0, top: 2.0)`.
   final EdgeInsetsGeometry? padding;

   /// Empty space to surround the [MaterialBanner].
   ///
   /// If the [margin] is null then this defaults to
   /// 0 if the banner's [elevation] is 0, 10 otherwise.
   final EdgeInsetsGeometry? margin;

   /// The amount of space by which to inset the [leading] widget.
   ///
   /// This defaults to `EdgeInsetsDirectional.only(end: 16.0)`.
   final EdgeInsetsGeometry? leadingPadding;

   /// An override to force the [actions] to be below the [content] regardless of
   /// how many there are.
   ///
   /// If this is true, the [actions] will be placed below the [content]. If
   /// this is false, the [actions] will be placed on the trailing side of the
   /// [content] if [actions]'s length is 1 and below the [content] if greater
   /// than 1.
   ///
   /// Defaults to false.
   final bool forceActionsBelow;

   /// The horizontal alignment of the [actions] when the [actions] laid out in a column.
   ///
   /// Defaults to [OverflowBarAlignment.end].
   final OverflowBarAlignment overflowAlignment;

   /// The animation driving the entrance and exit of the material banner when presented by the [ScaffoldMessenger].
   final Animation<double>? animation;

   /// Called the first time that the material banner is visible within a [Scaffold] when presented by the [ScaffoldMessenger].
   final VoidCallback? onVisible;

   // API for ScaffoldMessengerState.showMaterialBanner():

   /// Creates an animation controller useful for driving a [MaterialBanner]'s entrance and exit animation.
   static AnimationController createAnimationController({ required TickerProvider vsync }) {
     return AnimationController(
       duration: _materialBannerTransitionDuration,
       debugLabel: 'MaterialBanner',
       vsync: vsync,
     );
   }

   /// Creates a copy of this material banner but with the animation replaced with the given animation.
   ///
   /// If the original material banner lacks a key, the newly created material banner will
   /// use the given fallback key.
   MaterialBanner withAnimation(Animation<double> newAnimation, { Key? fallbackKey }) {
     return MaterialBanner(
       key: key ?? fallbackKey,
       content: content,
       contentTextStyle: contentTextStyle,
       actions: actions,
       elevation: elevation,
       leading: leading,
       backgroundColor: backgroundColor,
       padding: padding,
       margin: margin,
       leadingPadding: leadingPadding,
       forceActionsBelow: forceActionsBelow,
       overflowAlignment: overflowAlignment,
       animation: newAnimation,
       onVisible: onVisible,
     );
   }

   @override
   State<MaterialBanner> createState() => _MaterialBannerState();
 }

 class _MaterialBannerState extends State<MaterialBanner> {
   bool _wasVisible = false;

   @override
   void initState() {
     super.initState();
     widget.animation?.addStatusListener(_onAnimationStatusChanged);
   }

   @override
   void didUpdateWidget(MaterialBanner oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (widget.animation != oldWidget.animation) {
       oldWidget.animation?.removeStatusListener(_onAnimationStatusChanged);
       widget.animation?.addStatusListener(_onAnimationStatusChanged);
     }
   }

   @override
   void dispose() {
     widget.animation?.removeStatusListener(_onAnimationStatusChanged);
     super.dispose();
   }

   void _onAnimationStatusChanged(AnimationStatus animationStatus) {
     switch (animationStatus) {
       case AnimationStatus.dismissed:
       case AnimationStatus.forward:
       case AnimationStatus.reverse:
         break;
       case AnimationStatus.completed:
         if (widget.onVisible != null && !_wasVisible) {
           widget.onVisible!();
         }
         _wasVisible = true;
     }
   }

   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMediaQuery(context));
     final bool accessibleNavigation = MediaQuery.accessibleNavigationOf(context);

     assert(widget.actions.isNotEmpty);

     final ThemeData theme = Theme.of(context);
     final MaterialBannerThemeData bannerTheme = MaterialBannerTheme.of(context);
     final MaterialBannerThemeData defaults = theme.useMaterial3 ? _BannerDefaultsM3(context) : _BannerDefaultsM2(context);

     final bool isSingleRow = widget.actions.length == 1 && !widget.forceActionsBelow;
     final EdgeInsetsGeometry padding = widget.padding ?? bannerTheme.padding ?? (isSingleRow
         ? const EdgeInsetsDirectional.only(start: 16.0, top: 2.0)
         : const EdgeInsetsDirectional.only(start: 16.0, top: 24.0, end: 16.0, bottom: 4.0));
     final EdgeInsetsGeometry leadingPadding = widget.leadingPadding
         ?? bannerTheme.leadingPadding
         ?? const EdgeInsetsDirectional.only(end: 16.0);

     final Widget buttonBar = Container(
       alignment: AlignmentDirectional.centerEnd,
       constraints: const BoxConstraints(minHeight: 52.0),
       padding: const EdgeInsets.symmetric(horizontal: 8),
       child: OverflowBar(
         overflowAlignment: widget.overflowAlignment,
         spacing: 8,
         children: widget.actions,
       ),
     );

     final double elevation = widget.elevation ?? bannerTheme.elevation ?? 0.0;
     final EdgeInsetsGeometry margin = widget.margin ?? EdgeInsets.only(bottom: elevation > 0 ? 10.0 : 0.0);
     final Color backgroundColor = widget.backgroundColor
         ?? bannerTheme.backgroundColor
         ?? defaults.backgroundColor!;
     final Color? surfaceTintColor = widget.surfaceTintColor
         ?? bannerTheme.surfaceTintColor
         ?? defaults.surfaceTintColor;
     final Color? shadowColor = widget.shadowColor
         ?? bannerTheme.shadowColor;
     final Color? dividerColor = widget.dividerColor
         ?? bannerTheme.dividerColor
         ?? defaults.dividerColor;
     final TextStyle? textStyle = widget.contentTextStyle
         ?? bannerTheme.contentTextStyle
         ?? defaults.contentTextStyle;

     Widget materialBanner = Container(
       margin: margin,
       child: Material(
         elevation: elevation,
         color: backgroundColor,
         surfaceTintColor: surfaceTintColor,
         shadowColor: shadowColor,
         child: Column(
           mainAxisSize: MainAxisSize.min,
           children: <Widget>[
             Padding(
               padding: padding,
               child: Row(
                 children: <Widget>[
                   if (widget.leading != null)
                     Padding(
                       padding: leadingPadding,
                       child: widget.leading,
                     ),
                   Expanded(
                     child: DefaultTextStyle(
                       style: textStyle!,
                       child: widget.content,
                     ),
                   ),
                   if (isSingleRow)
                     buttonBar,
                 ],
               ),
             ),
             if (!isSingleRow)
               buttonBar,
             if (elevation == 0)
               Divider(height: 0, color: dividerColor),
           ],
         ),
       ),
     );

     // This provides a static banner for backwards compatibility.
     if (widget.animation == null) {
       return materialBanner;
     }

     materialBanner = SafeArea(
       child: materialBanner,
     );

     final CurvedAnimation heightAnimation = CurvedAnimation(parent: widget.animation!, curve: _materialBannerHeightCurve);
     final Animation<Offset> slideOutAnimation = Tween<Offset>(
       begin: const Offset(0.0, -1.0),
       end: Offset.zero,
     ).animate(CurvedAnimation(
       parent: widget.animation!,
       curve: const Threshold(0.0),
     ));

     materialBanner = Semantics(
       container: true,
       liveRegion: true,
       onDismiss: () {
         ScaffoldMessenger.of(context).removeCurrentMaterialBanner(reason: MaterialBannerClosedReason.dismiss);
       },
       child: accessibleNavigation
           ? materialBanner
           : SlideTransition(
         position: slideOutAnimation,
         child: materialBanner,
       ),
     );

     final Widget materialBannerTransition;
     if (accessibleNavigation) {
       materialBannerTransition = materialBanner;
     } else {
       materialBannerTransition = AnimatedBuilder(
         animation: heightAnimation,
         builder: (BuildContext context, Widget? child) {
           return Align(
             alignment: AlignmentDirectional.bottomStart,
             heightFactor: heightAnimation.value,
             child: child,
           );
         },
         child: materialBanner,
       );
     }

     return Hero(
       tag: '<MaterialBanner Hero tag - ${widget.content}>',
       child: ClipRect(child: materialBannerTransition),
     );
   }
 }

 class _BannerDefaultsM2 extends MaterialBannerThemeData {
   _BannerDefaultsM2(this.context)
     : _theme = Theme.of(context),
       super(elevation: 0.0);

   final BuildContext context;
   final ThemeData _theme;

   @override
   Color? get backgroundColor => _theme.colorScheme.surface;

   @override
   TextStyle? get contentTextStyle => _theme.textTheme.bodyMedium;
 }

 // BEGIN GENERATED TOKEN PROPERTIES - Banner

 // Do not edit by hand. The code between the "BEGIN GENERATED" and
 // "END GENERATED" comments are generated from data in the Material
 // Design token database by the script:
 //   dev/tools/gen_defaults/bin/gen_defaults.dart.

 // Token database version: v0_152

 class _BannerDefaultsM3 extends MaterialBannerThemeData {
   const _BannerDefaultsM3(this.context)
     : super(elevation: 1.0);

   final BuildContext context;

   @override
   Color? get backgroundColor => Theme.of(context).colorScheme.surface;

   @override
   Color? get surfaceTintColor => Theme.of(context).colorScheme.surfaceTint;

   @override
   Color? get dividerColor => Theme.of(context).colorScheme.outlineVariant;

   @override
   TextStyle? get contentTextStyle => Theme.of(context).textTheme.bodyMedium;
 }

 // END GENERATED TOKEN PROPERTIES - Banner
	// 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/widgets.dart';

	import 'banner_theme.dart';
	import 'divider.dart';
	import 'material.dart';
	import 'scaffold.dart';
	import 'theme.dart';

	// Examples can assume:
	// late BuildContext context;

	const Duration _materialBannerTransitionDuration = Duration(milliseconds: 250);
	const Curve _materialBannerHeightCurve = Curves.fastOutSlowIn;

	/// Specify how a [MaterialBanner] was closed.
	///
	/// The [ScaffoldMessengerState.showMaterialBanner] function returns a
	/// [ScaffoldFeatureController]. The value of the controller's closed property
	/// is a Future that resolves to a MaterialBannerClosedReason. Applications that need
	/// to know how a [MaterialBanner] was closed can use this value.
	///
	/// Example:
	///
	/// ```dart
	/// ScaffoldMessenger.of(context).showMaterialBanner(
	/// const MaterialBanner(
	/// content: Text('Message...'),
	/// actions: <Widget>[
	/// // ...
	/// ],
	/// )
	/// ).closed.then((MaterialBannerClosedReason reason) {
	/// // ...
	/// });
	/// ```
	enum MaterialBannerClosedReason {
	/// The material banner was closed through a [SemanticsAction.dismiss].
	dismiss,

	/// The material banner was closed by a user's swipe.
	swipe,

	/// The material banner was closed by the [ScaffoldFeatureController] close callback
	/// or by calling [ScaffoldMessengerState.hideCurrentMaterialBanner] directly.
	hide,

	/// The material banner was closed by a call to [ScaffoldMessengerState.removeCurrentMaterialBanner].
	remove,
	}

	/// A Material Design banner.
	///
	/// A banner displays an important, succinct message, and provides actions for
	/// users to address (or dismiss the banner). A user action is required for it
	/// to be dismissed.
	///
	/// Banners should be displayed at the top of the screen, below a top app bar.
	/// They are persistent and non-modal, allowing the user to either ignore them or
	/// interact with them at any time.
	///
	/// {@tool dartpad}
	/// Banners placed directly into the widget tree are static.
	///
	/// See code in examples/api/lib/material/banner/material_banner.0.dart
	/// {@end-tool}
	///
	/// {@tool dartpad}
	/// MaterialBanner's can also be presented through a [ScaffoldMessenger].
	/// Here is an example where ScaffoldMessengerState.showMaterialBanner() is used to show the MaterialBanner.
	///
	/// See code in examples/api/lib/material/banner/material_banner.1.dart
	/// {@end-tool}
	///
	/// The [actions] will be placed beside the [content] if there is only one.
	/// Otherwise, the [actions] will be placed below the [content]. Use
	/// [forceActionsBelow] to override this behavior.
	///
	/// If the [actions] placed below the [content], they will be laid out in a row.
	/// If there isn't sufficient room to display everything, they are laid out
	/// in a column instead.
	///
	/// The [actions] and [content] must be provided. An optional leading widget
	/// (typically an [Image]) can also be provided. The [contentTextStyle] and
	/// [backgroundColor] can be provided to customize the banner.
	///
	/// This widget is unrelated to the widgets library [Banner] widget.
	class MaterialBanner extends StatefulWidget {
	/// Creates a [MaterialBanner].
	///
	/// The [actions], [content], and [forceActionsBelow] must be non-null.
	/// The [actions].length must be greater than 0. The [elevation] must be null or
	/// non-negative.
	const MaterialBanner({
	super.key,
	required this.content,
	this.contentTextStyle,
	required this.actions,
	this.elevation,
	this.leading,
	this.backgroundColor,
	this.surfaceTintColor,
	this.shadowColor,
	this.dividerColor,
	this.padding,
	this.margin,
	this.leadingPadding,
	this.forceActionsBelow = false,
	this.overflowAlignment = OverflowBarAlignment.end,
	this.animation,
	this.onVisible,
	}) : assert(elevation == null \|\| elevation >= 0.0);

	/// The content of the [MaterialBanner].
	///
	/// Typically a [Text] widget.
	final Widget content;

	/// Style for the text in the [content] of the [MaterialBanner].
	///
	/// If `null`, [MaterialBannerThemeData.contentTextStyle] is used. If that is
	/// also `null`, [TextTheme.bodyMedium] of [ThemeData.textTheme] is used.
	final TextStyle? contentTextStyle;

	/// The set of actions that are displayed at the bottom or trailing side of
	/// the [MaterialBanner].
	///
	/// Typically this is a list of [TextButton] widgets.
	final List<Widget> actions;

	/// The z-coordinate at which to place the material banner.
	///
	/// This controls the size of the shadow below the material banner.
	///
	/// Defines the banner's [Material.elevation].
	///
	/// If this property is null, then [MaterialBannerThemeData.elevation] of
	/// [ThemeData.bannerTheme] is used, if that is also null, the default value is 0.
	/// If the elevation is 0, the [Scaffold]'s body will be pushed down by the
	/// MaterialBanner when used with [ScaffoldMessenger].
	final double? elevation;

	/// The (optional) leading widget of the [MaterialBanner].
	///
	/// Typically an [Icon] widget.
	final Widget? leading;

	/// The color of the surface of this [MaterialBanner].
	///
	/// If `null`, [MaterialBannerThemeData.backgroundColor] is used. If that is
	/// also `null`, [ColorScheme.surface] of [ThemeData.colorScheme] is used.
	final Color? backgroundColor;

	/// The color used as an overlay on [backgroundColor] to indicate elevation.
	///
	/// If null, [MaterialBannerThemeData.surfaceTintColor] is used. If that
	/// is also null, the default value is [ColorScheme.surfaceTint].
	///
	/// See [Material.surfaceTintColor] for more details on how this
	/// overlay is applied.
	final Color? surfaceTintColor;

	/// The color of the shadow below the [MaterialBanner].
	///
	/// If this property is null, then [MaterialBannerThemeData.shadowColor] of
	/// [ThemeData.bannerTheme] is used. If that is also null, the default value
	/// is null.
	final Color? shadowColor;

	/// The color of the divider.
	///
	/// If this property is null, then [MaterialBannerThemeData.dividerColor] of
	/// [ThemeData.bannerTheme] is used. If that is also null, the default value
	/// is [ColorScheme.surfaceVariant].
	final Color? dividerColor;

	/// The amount of space by which to inset the [content].
	///
	/// If the [actions] are below the [content], this defaults to
	/// `EdgeInsetsDirectional.only(start: 16.0, top: 24.0, end: 16.0, bottom: 4.0)`.
	///
	/// If the [actions] are trailing the [content], this defaults to
	/// `EdgeInsetsDirectional.only(start: 16.0, top: 2.0)`.
	final EdgeInsetsGeometry? padding;

	/// Empty space to surround the [MaterialBanner].
	///
	/// If the [margin] is null then this defaults to
	/// 0 if the banner's [elevation] is 0, 10 otherwise.
	final EdgeInsetsGeometry? margin;

	/// The amount of space by which to inset the [leading] widget.
	///
	/// This defaults to `EdgeInsetsDirectional.only(end: 16.0)`.
	final EdgeInsetsGeometry? leadingPadding;

	/// An override to force the [actions] to be below the [content] regardless of
	/// how many there are.
	///
	/// If this is true, the [actions] will be placed below the [content]. If
	/// this is false, the [actions] will be placed on the trailing side of the
	/// [content] if [actions]'s length is 1 and below the [content] if greater
	/// than 1.
	///
	/// Defaults to false.
	final bool forceActionsBelow;

	/// The horizontal alignment of the [actions] when the [actions] laid out in a column.
	///
	/// Defaults to [OverflowBarAlignment.end].
	final OverflowBarAlignment overflowAlignment;

	/// The animation driving the entrance and exit of the material banner when presented by the [ScaffoldMessenger].
	final Animation<double>? animation;

	/// Called the first time that the material banner is visible within a [Scaffold] when presented by the [ScaffoldMessenger].
	final VoidCallback? onVisible;

	// API for ScaffoldMessengerState.showMaterialBanner():

	/// Creates an animation controller useful for driving a [MaterialBanner]'s entrance and exit animation.
	static AnimationController createAnimationController({ required TickerProvider vsync }) {
	return AnimationController(
	duration: _materialBannerTransitionDuration,
	debugLabel: 'MaterialBanner',
	vsync: vsync,
	);
	}

	/// Creates a copy of this material banner but with the animation replaced with the given animation.
	///
	/// If the original material banner lacks a key, the newly created material banner will
	/// use the given fallback key.
	MaterialBanner withAnimation(Animation<double> newAnimation, { Key? fallbackKey }) {
	return MaterialBanner(
	key: key ?? fallbackKey,
	content: content,
	contentTextStyle: contentTextStyle,
	actions: actions,
	elevation: elevation,
	leading: leading,
	backgroundColor: backgroundColor,
	padding: padding,
	margin: margin,
	leadingPadding: leadingPadding,
	forceActionsBelow: forceActionsBelow,
	overflowAlignment: overflowAlignment,
	animation: newAnimation,
	onVisible: onVisible,
	);
	}

	@override
	State<MaterialBanner> createState() => _MaterialBannerState();
	}

	class _MaterialBannerState extends State<MaterialBanner> {
	bool _wasVisible = false;

	@override
	void initState() {
	super.initState();
	widget.animation?.addStatusListener(_onAnimationStatusChanged);
	}

	@override
	void didUpdateWidget(MaterialBanner oldWidget) {
	super.didUpdateWidget(oldWidget);
	if (widget.animation != oldWidget.animation) {
	oldWidget.animation?.removeStatusListener(_onAnimationStatusChanged);
	widget.animation?.addStatusListener(_onAnimationStatusChanged);
	}
	}

	@override
	void dispose() {
	widget.animation?.removeStatusListener(_onAnimationStatusChanged);
	super.dispose();
	}

	void _onAnimationStatusChanged(AnimationStatus animationStatus) {
	switch (animationStatus) {
	case AnimationStatus.dismissed:
	case AnimationStatus.forward:
	case AnimationStatus.reverse:
	break;
	case AnimationStatus.completed:
	if (widget.onVisible != null && !_wasVisible) {
	widget.onVisible!();
	}
	_wasVisible = true;
	}
	}

	@override
	Widget build(BuildContext context) {
	assert(debugCheckHasMediaQuery(context));
	final bool accessibleNavigation = MediaQuery.accessibleNavigationOf(context);

	assert(widget.actions.isNotEmpty);

	final ThemeData theme = Theme.of(context);
	final MaterialBannerThemeData bannerTheme = MaterialBannerTheme.of(context);
	final MaterialBannerThemeData defaults = theme.useMaterial3 ? _BannerDefaultsM3(context) : _BannerDefaultsM2(context);

	final bool isSingleRow = widget.actions.length == 1 && !widget.forceActionsBelow;
	final EdgeInsetsGeometry padding = widget.padding ?? bannerTheme.padding ?? (isSingleRow
	? const EdgeInsetsDirectional.only(start: 16.0, top: 2.0)
	: const EdgeInsetsDirectional.only(start: 16.0, top: 24.0, end: 16.0, bottom: 4.0));
	final EdgeInsetsGeometry leadingPadding = widget.leadingPadding
	?? bannerTheme.leadingPadding
	?? const EdgeInsetsDirectional.only(end: 16.0);

	final Widget buttonBar = Container(
	alignment: AlignmentDirectional.centerEnd,
	constraints: const BoxConstraints(minHeight: 52.0),
	padding: const EdgeInsets.symmetric(horizontal: 8),
	child: OverflowBar(
	overflowAlignment: widget.overflowAlignment,
	spacing: 8,
	children: widget.actions,
	),
	);

	final double elevation = widget.elevation ?? bannerTheme.elevation ?? 0.0;
	final EdgeInsetsGeometry margin = widget.margin ?? EdgeInsets.only(bottom: elevation > 0 ? 10.0 : 0.0);
	final Color backgroundColor = widget.backgroundColor
	?? bannerTheme.backgroundColor
	?? defaults.backgroundColor!;
	final Color? surfaceTintColor = widget.surfaceTintColor
	?? bannerTheme.surfaceTintColor
	?? defaults.surfaceTintColor;
	final Color? shadowColor = widget.shadowColor
	?? bannerTheme.shadowColor;
	final Color? dividerColor = widget.dividerColor
	?? bannerTheme.dividerColor
	?? defaults.dividerColor;
	final TextStyle? textStyle = widget.contentTextStyle
	?? bannerTheme.contentTextStyle
	?? defaults.contentTextStyle;

	Widget materialBanner = Container(
	margin: margin,
	child: Material(
	elevation: elevation,
	color: backgroundColor,
	surfaceTintColor: surfaceTintColor,
	shadowColor: shadowColor,
	child: Column(
	mainAxisSize: MainAxisSize.min,
	children: <Widget>[
	Padding(
	padding: padding,
	child: Row(
	children: <Widget>[
	if (widget.leading != null)
	Padding(
	padding: leadingPadding,
	child: widget.leading,
	),
	Expanded(
	child: DefaultTextStyle(
	style: textStyle!,
	child: widget.content,
	),
	),
	if (isSingleRow)
	buttonBar,
	],
	),
	),
	if (!isSingleRow)
	buttonBar,
	if (elevation == 0)
	Divider(height: 0, color: dividerColor),
	],
	),
	),
	);

	// This provides a static banner for backwards compatibility.
	if (widget.animation == null) {
	return materialBanner;
	}

	materialBanner = SafeArea(
	child: materialBanner,
	);

	final CurvedAnimation heightAnimation = CurvedAnimation(parent: widget.animation!, curve: _materialBannerHeightCurve);
	final Animation<Offset> slideOutAnimation = Tween<Offset>(
	begin: const Offset(0.0, -1.0),
	end: Offset.zero,
	).animate(CurvedAnimation(
	parent: widget.animation!,
	curve: const Threshold(0.0),
	));

	materialBanner = Semantics(
	container: true,
	liveRegion: true,
	onDismiss: () {
	ScaffoldMessenger.of(context).removeCurrentMaterialBanner(reason: MaterialBannerClosedReason.dismiss);
	},
	child: accessibleNavigation
	? materialBanner
	: SlideTransition(
	position: slideOutAnimation,
	child: materialBanner,
	),
	);

	final Widget materialBannerTransition;
	if (accessibleNavigation) {
	materialBannerTransition = materialBanner;
	} else {
	materialBannerTransition = AnimatedBuilder(
	animation: heightAnimation,
	builder: (BuildContext context, Widget? child) {
	return Align(
	alignment: AlignmentDirectional.bottomStart,
	heightFactor: heightAnimation.value,
	child: child,
	);
	},
	child: materialBanner,
	);
	}

	return Hero(
	tag: '<MaterialBanner Hero tag - ${widget.content}>',
	child: ClipRect(child: materialBannerTransition),
	);
	}
	}

	class _BannerDefaultsM2 extends MaterialBannerThemeData {
	_BannerDefaultsM2(this.context)
	: _theme = Theme.of(context),
	super(elevation: 0.0);

	final BuildContext context;
	final ThemeData _theme;

	@override
	Color? get backgroundColor => _theme.colorScheme.surface;

	@override
	TextStyle? get contentTextStyle => _theme.textTheme.bodyMedium;
	}

	// BEGIN GENERATED TOKEN PROPERTIES - Banner

	// Do not edit by hand. The code between the "BEGIN GENERATED" and
	// "END GENERATED" comments are generated from data in the Material
	// Design token database by the script:
	// dev/tools/gen_defaults/bin/gen_defaults.dart.

	// Token database version: v0_152

	class _BannerDefaultsM3 extends MaterialBannerThemeData {
	const _BannerDefaultsM3(this.context)
	: super(elevation: 1.0);

	final BuildContext context;

	@override
	Color? get backgroundColor => Theme.of(context).colorScheme.surface;

	@override
	Color? get surfaceTintColor => Theme.of(context).colorScheme.surfaceTint;

	@override
	Color? get dividerColor => Theme.of(context).colorScheme.outlineVariant;

	@override
	TextStyle? get contentTextStyle => Theme.of(context).textTheme.bodyMedium;
	}

	// END GENERATED TOKEN PROPERTIES - Banner