packages/flutter/lib/src/material/snack_bar.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/rendering.dart';
 import 'package:flutter/widgets.dart';

 import 'button_theme.dart';
 import 'color_scheme.dart';
 import 'flat_button.dart';
 import 'material.dart';
 import 'scaffold.dart';
 import 'snack_bar_theme.dart';
 import 'theme.dart';
 import 'theme_data.dart';

 const double _singleLineVerticalPadding = 14.0;

 // TODO(ianh): We should check if the given text and actions are going to fit on
 // one line or not, and if they are, use the single-line layout, and if not, use
 // the multiline layout. See link above.

 // TODO(ianh): Implement the Tablet version of snackbar if we're "on a tablet".

 const Duration _snackBarTransitionDuration = Duration(milliseconds: 250);
 const Duration _snackBarDisplayDuration = Duration(milliseconds: 4000);
 const Curve _snackBarHeightCurve = Curves.fastOutSlowIn;
 const Curve _snackBarFadeInCurve = Interval(0.45, 1.0, curve: Curves.fastOutSlowIn);
 const Curve _snackBarFadeOutCurve = Interval(0.72, 1.0, curve: Curves.fastOutSlowIn);

 /// Specify how a [SnackBar] was closed.
 ///
 /// The [ScaffoldState.showSnackBar] function returns a
 /// [ScaffoldFeatureController]. The value of the controller's closed property
 /// is a Future that resolves to a SnackBarClosedReason. Applications that need
 /// to know how a snackbar was closed can use this value.
 ///
 /// Example:
 ///
 /// ```dart
 /// Scaffold.of(context).showSnackBar(
 ///   SnackBar( ... )
 /// ).closed.then((SnackBarClosedReason reason) {
 ///    ...
 /// });
 /// ```
 enum SnackBarClosedReason {
   /// The snack bar was closed after the user tapped a [SnackBarAction].
   action,

   /// The snack bar was closed through a [SemanticAction.dismiss].
   dismiss,

   /// The snack bar was closed by a user's swipe.
   swipe,

   /// The snack bar was closed by the [ScaffoldFeatureController] close callback
   /// or by calling [ScaffoldState.hideCurrentSnackBar] directly.
   hide,

   /// The snack bar was closed by an call to [ScaffoldState.removeCurrentSnackBar].
   remove,

   /// The snack bar was closed because its timer expired.
   timeout,
 }

 /// A button for a [SnackBar], known as an "action".
 ///
 /// Snack bar actions are always enabled. If you want to disable a snack bar
 /// action, simply don't include it in the snack bar.
 ///
 /// Snack bar actions can only be pressed once. Subsequent presses are ignored.
 ///
 /// See also:
 ///
 ///  * [SnackBar]
 ///  * <https://material.io/design/components/snackbars.html>
 class SnackBarAction extends StatefulWidget {
   /// Creates an action for a [SnackBar].
   ///
   /// The [label] and [onPressed] arguments must be non-null.
   const SnackBarAction({
     Key key,
     this.textColor,
     this.disabledTextColor,
     @required this.label,
     @required this.onPressed,
   }) : assert(label != null),
        assert(onPressed != null),
        super(key: key);

   /// The button label color. If not provided, defaults to [accentColor].
   final Color textColor;

   /// The button disabled label color. This color is shown after the
   /// [snackBarAction] is dismissed.
   final Color disabledTextColor;

   /// The button label.
   final String label;

   /// The callback to be called when the button is pressed. Must not be null.
   ///
   /// This callback will be called at most once each time this action is
   /// displayed in a [SnackBar].
   final VoidCallback onPressed;

   @override
   _SnackBarActionState createState() => _SnackBarActionState();
 }

 class _SnackBarActionState extends State<SnackBarAction> {
   bool _haveTriggeredAction = false;

   void _handlePressed() {
     if (_haveTriggeredAction)
       return;
     setState(() {
       _haveTriggeredAction = true;
     });
     widget.onPressed();
     Scaffold.of(context).hideCurrentSnackBar(reason: SnackBarClosedReason.action);
   }

   @override
   Widget build(BuildContext context) {
     final SnackBarThemeData snackBarTheme = Theme.of(context).snackBarTheme;
     final Color textColor = widget.textColor ?? snackBarTheme.actionTextColor;
     final Color disabledTextColor = widget.disabledTextColor ?? snackBarTheme.disabledActionTextColor;

     return FlatButton(
       onPressed: _haveTriggeredAction ? null : _handlePressed,
       child: Text(widget.label),
       textColor: textColor,
       disabledTextColor: disabledTextColor,
     );
   }
 }

 /// A lightweight message with an optional action which briefly displays at the
 /// bottom of the screen.
 ///
 /// To display a snack bar, call `Scaffold.of(context).showSnackBar()`, passing
 /// an instance of [SnackBar] that describes the message.
 ///
 /// To control how long the [SnackBar] remains visible, specify a [duration].
 ///
 /// A SnackBar with an action will not time out when TalkBack or VoiceOver are
 /// enabled. This is controlled by [AccessibilityFeatures.accessibleNavigation].
 ///
 /// See also:
 ///
 ///  * [Scaffold.of], to obtain the current [ScaffoldState], which manages the
 ///    display and animation of snack bars.
 ///  * [ScaffoldState.showSnackBar], which displays a [SnackBar].
 ///  * [ScaffoldState.removeCurrentSnackBar], which abruptly hides the currently
 ///    displayed snack bar, if any, and allows the next to be displayed.
 ///  * [SnackBarAction], which is used to specify an [action] button to show
 ///    on the snack bar.
 ///  * [SnackBarThemeData], to configure the default property values for
 ///    [SnackBar] widgets.
 ///  * <https://material.io/design/components/snackbars.html>
 class SnackBar extends StatefulWidget {
   /// Creates a snack bar.
   ///
   /// The [content] argument must be non-null. The [elevation] must be null or
   /// non-negative.
   const SnackBar({
     Key key,
     @required this.content,
     this.backgroundColor,
     this.elevation,
     this.shape,
     this.behavior,
     this.action,
     this.duration = _snackBarDisplayDuration,
     this.animation,
     this.onVisible,
   }) : assert(elevation == null || elevation >= 0.0),
        assert(content != null),
        assert(duration != null),
        super(key: key);

   /// The primary content of the snack bar.
   ///
   /// Typically a [Text] widget.
   final Widget content;

   /// The Snackbar's background color. If not specified it will use
   /// [ThemeData.snackBarTheme.backgroundColor]. If that is not specified
   /// it will default to a dark variation of [ColorScheme.surface] for light
   /// themes, or [ColorScheme.onSurface] for dark themes.
   final Color backgroundColor;

   /// The z-coordinate at which to place the snack bar. This controls the size
   /// of the shadow below the snack bar.
   ///
   /// Defines the card's [Material.elevation].
   ///
   /// If this property is null, then [ThemeData.snackBarTheme.elevation] is
   /// used, if that is also null, the default value is 6.0.
   final double elevation;

   /// The shape of the snack bar's [Material].
   ///
   /// Defines the snack bar's [Material.shape].
   ///
   /// If this property is null then [ThemeData.snackBarTheme.shape] is used.
   /// If that's null then the shape will depend on the [SnackBarBehavior]. For
   /// [SnackBarBehavior.fixed], no overriding shape is specified, so the
   /// [SnackBar] is rectangular. For [SnackBarBehavior.floating], it uses a
   /// [RoundedRectangleBorder] with a circular corner radius of 4.0.
   final ShapeBorder shape;

   /// This defines the behavior and location of the snack bar.
   ///
   /// Defines where a [SnackBar] should appear within a [Scaffold] and how its
   /// location should be adjusted when the scaffold also includes a
   /// [FloatingActionButton] or a [BottomNavigationBar]
   ///
   /// If this property is null, then [ThemeData.snackBarTheme.behavior]
   /// is used. If that is null, then the default is [SnackBarBehavior.fixed].
   final SnackBarBehavior behavior;

   /// (optional) An action that the user can take based on the snack bar.
   ///
   /// For example, the snack bar might let the user undo the operation that
   /// prompted the snackbar. Snack bars can have at most one action.
   ///
   /// The action should not be "dismiss" or "cancel".
   final SnackBarAction action;

   /// The amount of time the snack bar should be displayed.
   ///
   /// Defaults to 4.0s.
   ///
   /// See also:
   ///
   ///  * [ScaffoldState.removeCurrentSnackBar], which abruptly hides the
   ///    currently displayed snack bar, if any, and allows the next to be
   ///    displayed.
   ///  * <https://material.io/design/components/snackbars.html>
   final Duration duration;

   /// The animation driving the entrance and exit of the snack bar.
   final Animation<double> animation;

   /// Called the first time that the snackbar is visible within a [Scaffold].
   final VoidCallback onVisible;

   // API for Scaffold.showSnackBar():

   /// Creates an animation controller useful for driving a snack bar's entrance and exit animation.
   static AnimationController createAnimationController({ @required TickerProvider vsync }) {
     return AnimationController(
       duration: _snackBarTransitionDuration,
       debugLabel: 'SnackBar',
       vsync: vsync,
     );
   }

   /// Creates a copy of this snack bar but with the animation replaced with the given animation.
   ///
   /// If the original snack bar lacks a key, the newly created snack bar will
   /// use the given fallback key.
   SnackBar withAnimation(Animation<double> newAnimation, { Key fallbackKey }) {
     return SnackBar(
       key: key ?? fallbackKey,
       content: content,
       backgroundColor: backgroundColor,
       elevation: elevation,
       shape: shape,
       behavior: behavior,
       action: action,
       duration: duration,
       animation: newAnimation,
       onVisible: onVisible,
     );
   }

   @override
   State<SnackBar> createState() => _SnackBarState();
 }


 class _SnackBarState extends State<SnackBar> {
   bool _wasVisible = false;

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

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

   @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) {
     final MediaQueryData mediaQueryData = MediaQuery.of(context);
     assert(widget.animation != null);
     final ThemeData theme = Theme.of(context);
     final ColorScheme colorScheme = theme.colorScheme;
     final SnackBarThemeData snackBarTheme = theme.snackBarTheme;
     final bool isThemeDark = theme.brightness == Brightness.dark;

     // SnackBar uses a theme that is the opposite brightness from
     // the surrounding theme.
     final Brightness brightness = isThemeDark ? Brightness.light : Brightness.dark;
     final Color themeBackgroundColor = isThemeDark
       ? colorScheme.onSurface
       : Color.alphaBlend(colorScheme.onSurface.withOpacity(0.80), colorScheme.surface);
     final ThemeData inverseTheme = ThemeData(
       brightness: brightness,
       backgroundColor: themeBackgroundColor,
       colorScheme: ColorScheme(
         primary: colorScheme.onPrimary,
         primaryVariant: colorScheme.onPrimary,
         // For the button color, the spec says it should be primaryVariant, but for
         // backward compatibility on light themes we are leaving it as secondary.
         secondary: isThemeDark ? colorScheme.primaryVariant : colorScheme.secondary,
         secondaryVariant: colorScheme.onSecondary,
         surface: colorScheme.onSurface,
         background: themeBackgroundColor,
         error: colorScheme.onError,
         onPrimary: colorScheme.primary,
         onSecondary: colorScheme.secondary,
         onSurface: colorScheme.surface,
         onBackground: colorScheme.background,
         onError: colorScheme.error,
         brightness: brightness,
       ),
       snackBarTheme: snackBarTheme,
     );

     final TextStyle contentTextStyle = snackBarTheme.contentTextStyle ?? inverseTheme.textTheme.subtitle1;
     final SnackBarBehavior snackBarBehavior = widget.behavior ?? snackBarTheme.behavior ?? SnackBarBehavior.fixed;
     final bool isFloatingSnackBar = snackBarBehavior == SnackBarBehavior.floating;
     final double snackBarPadding = isFloatingSnackBar ? 16.0 : 24.0;

     final CurvedAnimation heightAnimation = CurvedAnimation(parent: widget.animation, curve: _snackBarHeightCurve);
     final CurvedAnimation fadeInAnimation = CurvedAnimation(parent: widget.animation, curve: _snackBarFadeInCurve);
     final CurvedAnimation fadeOutAnimation = CurvedAnimation(
       parent: widget.animation,
       curve: _snackBarFadeOutCurve,
       reverseCurve: const Threshold(0.0),
     );

     Widget snackBar = SafeArea(
       top: false,
       bottom: !isFloatingSnackBar,
       child: Row(
         crossAxisAlignment: CrossAxisAlignment.center,
         children: <Widget>[
           SizedBox(width: snackBarPadding),
           Expanded(
             child: Container(
               padding: const EdgeInsets.symmetric(vertical: _singleLineVerticalPadding),
               child: DefaultTextStyle(
                 style: contentTextStyle,
                 child: widget.content,
               ),
             ),
           ),
           if (widget.action != null)
             ButtonTheme(
               textTheme: ButtonTextTheme.accent,
               minWidth: 64.0,
               padding: EdgeInsets.symmetric(horizontal: snackBarPadding),
               child: widget.action,
             )
           else
             SizedBox(width: snackBarPadding),
         ],
       ),
     );

     final double elevation = widget.elevation ?? snackBarTheme.elevation ?? 6.0;
     final Color backgroundColor = widget.backgroundColor ?? snackBarTheme.backgroundColor ?? inverseTheme.backgroundColor;
     final ShapeBorder shape = widget.shape
       ?? snackBarTheme.shape
       ?? (isFloatingSnackBar ? RoundedRectangleBorder(borderRadius: BorderRadius.circular(4.0)) : null);

     snackBar = Material(
       shape: shape,
       elevation: elevation,
       color: backgroundColor,
       child: Theme(
         data: inverseTheme,
         child: mediaQueryData.accessibleNavigation
             ? snackBar
             : FadeTransition(
                 opacity: fadeOutAnimation,
                 child: snackBar,
               ),
       ),
     );

     if (isFloatingSnackBar) {
       snackBar = Padding(
         padding: const EdgeInsets.fromLTRB(15.0, 5.0, 15.0, 10.0),
         child: snackBar,
       );
     }

     snackBar = Semantics(
       container: true,
       liveRegion: true,
       onDismiss: () {
         Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.dismiss);
       },
       child: Dismissible(
         key: const Key('dismissible'),
         direction: DismissDirection.down,
         resizeDuration: null,
         onDismissed: (DismissDirection direction) {
           Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.swipe);
         },
         child: snackBar,
       ),
     );

     Widget snackBarTransition;
     if (mediaQueryData.accessibleNavigation) {
       snackBarTransition = snackBar;
     } else if (isFloatingSnackBar) {
       snackBarTransition = FadeTransition(
         opacity: fadeInAnimation,
         child: snackBar,
       );
     } else {
       snackBarTransition = AnimatedBuilder(
         animation: heightAnimation,
         builder: (BuildContext context, Widget child) {
           return Align(
             alignment: AlignmentDirectional.topStart,
             heightFactor: heightAnimation.value,
             child: child,
           );
         },
         child: snackBar,
       );
     }

     return ClipRect(child: snackBarTransition);
   }
 }
	// 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 'package:flutter/widgets.dart';

	import 'button_theme.dart';
	import 'color_scheme.dart';
	import 'flat_button.dart';
	import 'material.dart';
	import 'scaffold.dart';
	import 'snack_bar_theme.dart';
	import 'theme.dart';
	import 'theme_data.dart';

	const double _singleLineVerticalPadding = 14.0;

	// TODO(ianh): We should check if the given text and actions are going to fit on
	// one line or not, and if they are, use the single-line layout, and if not, use
	// the multiline layout. See link above.

	// TODO(ianh): Implement the Tablet version of snackbar if we're "on a tablet".

	const Duration _snackBarTransitionDuration = Duration(milliseconds: 250);
	const Duration _snackBarDisplayDuration = Duration(milliseconds: 4000);
	const Curve _snackBarHeightCurve = Curves.fastOutSlowIn;
	const Curve _snackBarFadeInCurve = Interval(0.45, 1.0, curve: Curves.fastOutSlowIn);
	const Curve _snackBarFadeOutCurve = Interval(0.72, 1.0, curve: Curves.fastOutSlowIn);

	/// Specify how a [SnackBar] was closed.
	///
	/// The [ScaffoldState.showSnackBar] function returns a
	/// [ScaffoldFeatureController]. The value of the controller's closed property
	/// is a Future that resolves to a SnackBarClosedReason. Applications that need
	/// to know how a snackbar was closed can use this value.
	///
	/// Example:
	///
	/// ```dart
	/// Scaffold.of(context).showSnackBar(
	/// SnackBar( ... )
	/// ).closed.then((SnackBarClosedReason reason) {
	/// ...
	/// });
	/// ```
	enum SnackBarClosedReason {
	/// The snack bar was closed after the user tapped a [SnackBarAction].
	action,

	/// The snack bar was closed through a [SemanticAction.dismiss].
	dismiss,

	/// The snack bar was closed by a user's swipe.
	swipe,

	/// The snack bar was closed by the [ScaffoldFeatureController] close callback
	/// or by calling [ScaffoldState.hideCurrentSnackBar] directly.
	hide,

	/// The snack bar was closed by an call to [ScaffoldState.removeCurrentSnackBar].
	remove,

	/// The snack bar was closed because its timer expired.
	timeout,
	}

	/// A button for a [SnackBar], known as an "action".
	///
	/// Snack bar actions are always enabled. If you want to disable a snack bar
	/// action, simply don't include it in the snack bar.
	///
	/// Snack bar actions can only be pressed once. Subsequent presses are ignored.
	///
	/// See also:
	///
	/// * [SnackBar]
	/// * <https://material.io/design/components/snackbars.html>
	class SnackBarAction extends StatefulWidget {
	/// Creates an action for a [SnackBar].
	///
	/// The [label] and [onPressed] arguments must be non-null.
	const SnackBarAction({
	Key key,
	this.textColor,
	this.disabledTextColor,
	@required this.label,
	@required this.onPressed,
	}) : assert(label != null),
	assert(onPressed != null),
	super(key: key);

	/// The button label color. If not provided, defaults to [accentColor].
	final Color textColor;

	/// The button disabled label color. This color is shown after the
	/// [snackBarAction] is dismissed.
	final Color disabledTextColor;

	/// The button label.
	final String label;

	/// The callback to be called when the button is pressed. Must not be null.
	///
	/// This callback will be called at most once each time this action is
	/// displayed in a [SnackBar].
	final VoidCallback onPressed;

	@override
	_SnackBarActionState createState() => _SnackBarActionState();
	}

	class _SnackBarActionState extends State<SnackBarAction> {
	bool _haveTriggeredAction = false;

	void _handlePressed() {
	if (_haveTriggeredAction)
	return;
	setState(() {
	_haveTriggeredAction = true;
	});
	widget.onPressed();
	Scaffold.of(context).hideCurrentSnackBar(reason: SnackBarClosedReason.action);
	}

	@override
	Widget build(BuildContext context) {
	final SnackBarThemeData snackBarTheme = Theme.of(context).snackBarTheme;
	final Color textColor = widget.textColor ?? snackBarTheme.actionTextColor;
	final Color disabledTextColor = widget.disabledTextColor ?? snackBarTheme.disabledActionTextColor;

	return FlatButton(
	onPressed: _haveTriggeredAction ? null : _handlePressed,
	child: Text(widget.label),
	textColor: textColor,
	disabledTextColor: disabledTextColor,
	);
	}
	}

	/// A lightweight message with an optional action which briefly displays at the
	/// bottom of the screen.
	///
	/// To display a snack bar, call `Scaffold.of(context).showSnackBar()`, passing
	/// an instance of [SnackBar] that describes the message.
	///
	/// To control how long the [SnackBar] remains visible, specify a [duration].
	///
	/// A SnackBar with an action will not time out when TalkBack or VoiceOver are
	/// enabled. This is controlled by [AccessibilityFeatures.accessibleNavigation].
	///
	/// See also:
	///
	/// * [Scaffold.of], to obtain the current [ScaffoldState], which manages the
	/// display and animation of snack bars.
	/// * [ScaffoldState.showSnackBar], which displays a [SnackBar].
	/// * [ScaffoldState.removeCurrentSnackBar], which abruptly hides the currently
	/// displayed snack bar, if any, and allows the next to be displayed.
	/// * [SnackBarAction], which is used to specify an [action] button to show
	/// on the snack bar.
	/// * [SnackBarThemeData], to configure the default property values for
	/// [SnackBar] widgets.
	/// * <https://material.io/design/components/snackbars.html>
	class SnackBar extends StatefulWidget {
	/// Creates a snack bar.
	///
	/// The [content] argument must be non-null. The [elevation] must be null or
	/// non-negative.
	const SnackBar({
	Key key,
	@required this.content,
	this.backgroundColor,
	this.elevation,
	this.shape,
	this.behavior,
	this.action,
	this.duration = _snackBarDisplayDuration,
	this.animation,
	this.onVisible,
	}) : assert(elevation == null \|\| elevation >= 0.0),
	assert(content != null),
	assert(duration != null),
	super(key: key);

	/// The primary content of the snack bar.
	///
	/// Typically a [Text] widget.
	final Widget content;

	/// The Snackbar's background color. If not specified it will use
	/// [ThemeData.snackBarTheme.backgroundColor]. If that is not specified
	/// it will default to a dark variation of [ColorScheme.surface] for light
	/// themes, or [ColorScheme.onSurface] for dark themes.
	final Color backgroundColor;

	/// The z-coordinate at which to place the snack bar. This controls the size
	/// of the shadow below the snack bar.
	///
	/// Defines the card's [Material.elevation].
	///
	/// If this property is null, then [ThemeData.snackBarTheme.elevation] is
	/// used, if that is also null, the default value is 6.0.
	final double elevation;

	/// The shape of the snack bar's [Material].
	///
	/// Defines the snack bar's [Material.shape].
	///
	/// If this property is null then [ThemeData.snackBarTheme.shape] is used.
	/// If that's null then the shape will depend on the [SnackBarBehavior]. For
	/// [SnackBarBehavior.fixed], no overriding shape is specified, so the
	/// [SnackBar] is rectangular. For [SnackBarBehavior.floating], it uses a
	/// [RoundedRectangleBorder] with a circular corner radius of 4.0.
	final ShapeBorder shape;

	/// This defines the behavior and location of the snack bar.
	///
	/// Defines where a [SnackBar] should appear within a [Scaffold] and how its
	/// location should be adjusted when the scaffold also includes a
	/// [FloatingActionButton] or a [BottomNavigationBar]
	///
	/// If this property is null, then [ThemeData.snackBarTheme.behavior]
	/// is used. If that is null, then the default is [SnackBarBehavior.fixed].
	final SnackBarBehavior behavior;

	/// (optional) An action that the user can take based on the snack bar.
	///
	/// For example, the snack bar might let the user undo the operation that
	/// prompted the snackbar. Snack bars can have at most one action.
	///
	/// The action should not be "dismiss" or "cancel".
	final SnackBarAction action;

	/// The amount of time the snack bar should be displayed.
	///
	/// Defaults to 4.0s.
	///
	/// See also:
	///
	/// * [ScaffoldState.removeCurrentSnackBar], which abruptly hides the
	/// currently displayed snack bar, if any, and allows the next to be
	/// displayed.
	/// * <https://material.io/design/components/snackbars.html>
	final Duration duration;

	/// The animation driving the entrance and exit of the snack bar.
	final Animation<double> animation;

	/// Called the first time that the snackbar is visible within a [Scaffold].
	final VoidCallback onVisible;

	// API for Scaffold.showSnackBar():

	/// Creates an animation controller useful for driving a snack bar's entrance and exit animation.
	static AnimationController createAnimationController({ @required TickerProvider vsync }) {
	return AnimationController(
	duration: _snackBarTransitionDuration,
	debugLabel: 'SnackBar',
	vsync: vsync,
	);
	}

	/// Creates a copy of this snack bar but with the animation replaced with the given animation.
	///
	/// If the original snack bar lacks a key, the newly created snack bar will
	/// use the given fallback key.
	SnackBar withAnimation(Animation<double> newAnimation, { Key fallbackKey }) {
	return SnackBar(
	key: key ?? fallbackKey,
	content: content,
	backgroundColor: backgroundColor,
	elevation: elevation,
	shape: shape,
	behavior: behavior,
	action: action,
	duration: duration,
	animation: newAnimation,
	onVisible: onVisible,
	);
	}

	@override
	State<SnackBar> createState() => _SnackBarState();
	}


	class _SnackBarState extends State<SnackBar> {
	bool _wasVisible = false;

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

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

	@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) {
	final MediaQueryData mediaQueryData = MediaQuery.of(context);
	assert(widget.animation != null);
	final ThemeData theme = Theme.of(context);
	final ColorScheme colorScheme = theme.colorScheme;
	final SnackBarThemeData snackBarTheme = theme.snackBarTheme;
	final bool isThemeDark = theme.brightness == Brightness.dark;

	// SnackBar uses a theme that is the opposite brightness from
	// the surrounding theme.
	final Brightness brightness = isThemeDark ? Brightness.light : Brightness.dark;
	final Color themeBackgroundColor = isThemeDark
	? colorScheme.onSurface
	: Color.alphaBlend(colorScheme.onSurface.withOpacity(0.80), colorScheme.surface);
	final ThemeData inverseTheme = ThemeData(
	brightness: brightness,
	backgroundColor: themeBackgroundColor,
	colorScheme: ColorScheme(
	primary: colorScheme.onPrimary,
	primaryVariant: colorScheme.onPrimary,
	// For the button color, the spec says it should be primaryVariant, but for
	// backward compatibility on light themes we are leaving it as secondary.
	secondary: isThemeDark ? colorScheme.primaryVariant : colorScheme.secondary,
	secondaryVariant: colorScheme.onSecondary,
	surface: colorScheme.onSurface,
	background: themeBackgroundColor,
	error: colorScheme.onError,
	onPrimary: colorScheme.primary,
	onSecondary: colorScheme.secondary,
	onSurface: colorScheme.surface,
	onBackground: colorScheme.background,
	onError: colorScheme.error,
	brightness: brightness,
	),
	snackBarTheme: snackBarTheme,
	);

	final TextStyle contentTextStyle = snackBarTheme.contentTextStyle ?? inverseTheme.textTheme.subtitle1;
	final SnackBarBehavior snackBarBehavior = widget.behavior ?? snackBarTheme.behavior ?? SnackBarBehavior.fixed;
	final bool isFloatingSnackBar = snackBarBehavior == SnackBarBehavior.floating;
	final double snackBarPadding = isFloatingSnackBar ? 16.0 : 24.0;

	final CurvedAnimation heightAnimation = CurvedAnimation(parent: widget.animation, curve: _snackBarHeightCurve);
	final CurvedAnimation fadeInAnimation = CurvedAnimation(parent: widget.animation, curve: _snackBarFadeInCurve);
	final CurvedAnimation fadeOutAnimation = CurvedAnimation(
	parent: widget.animation,
	curve: _snackBarFadeOutCurve,
	reverseCurve: const Threshold(0.0),
	);

	Widget snackBar = SafeArea(
	top: false,
	bottom: !isFloatingSnackBar,
	child: Row(
	crossAxisAlignment: CrossAxisAlignment.center,
	children: <Widget>[
	SizedBox(width: snackBarPadding),
	Expanded(
	child: Container(
	padding: const EdgeInsets.symmetric(vertical: _singleLineVerticalPadding),
	child: DefaultTextStyle(
	style: contentTextStyle,
	child: widget.content,
	),
	),
	),
	if (widget.action != null)
	ButtonTheme(
	textTheme: ButtonTextTheme.accent,
	minWidth: 64.0,
	padding: EdgeInsets.symmetric(horizontal: snackBarPadding),
	child: widget.action,
	)
	else
	SizedBox(width: snackBarPadding),
	],
	),
	);

	final double elevation = widget.elevation ?? snackBarTheme.elevation ?? 6.0;
	final Color backgroundColor = widget.backgroundColor ?? snackBarTheme.backgroundColor ?? inverseTheme.backgroundColor;
	final ShapeBorder shape = widget.shape
	?? snackBarTheme.shape
	?? (isFloatingSnackBar ? RoundedRectangleBorder(borderRadius: BorderRadius.circular(4.0)) : null);

	snackBar = Material(
	shape: shape,
	elevation: elevation,
	color: backgroundColor,
	child: Theme(
	data: inverseTheme,
	child: mediaQueryData.accessibleNavigation
	? snackBar
	: FadeTransition(
	opacity: fadeOutAnimation,
	child: snackBar,
	),
	),
	);

	if (isFloatingSnackBar) {
	snackBar = Padding(
	padding: const EdgeInsets.fromLTRB(15.0, 5.0, 15.0, 10.0),
	child: snackBar,
	);
	}

	snackBar = Semantics(
	container: true,
	liveRegion: true,
	onDismiss: () {
	Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.dismiss);
	},
	child: Dismissible(
	key: const Key('dismissible'),
	direction: DismissDirection.down,
	resizeDuration: null,
	onDismissed: (DismissDirection direction) {
	Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.swipe);
	},
	child: snackBar,
	),
	);

	Widget snackBarTransition;
	if (mediaQueryData.accessibleNavigation) {
	snackBarTransition = snackBar;
	} else if (isFloatingSnackBar) {
	snackBarTransition = FadeTransition(
	opacity: fadeInAnimation,
	child: snackBar,
	);
	} else {
	snackBarTransition = AnimatedBuilder(
	animation: heightAnimation,
	builder: (BuildContext context, Widget child) {
	return Align(
	alignment: AlignmentDirectional.topStart,
	heightFactor: heightAnimation.value,
	child: child,
	);
	},
	child: snackBar,
	);
	}

	return ClipRect(child: snackBarTransition);
	}
	}