examples/flutter_gallery/lib/demo/shrine/backdrop.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/material.dart';
 import 'package:meta/meta.dart';

 import 'package:flutter_gallery/demo/shrine/login.dart';

 const Cubic _kAccelerateCurve = Cubic(0.548, 0.0, 0.757, 0.464);
 const Cubic _kDecelerateCurve = Cubic(0.23, 0.94, 0.41, 1.0);
 const double _kPeakVelocityTime = 0.248210;
 const double _kPeakVelocityProgress = 0.379146;

 class _TappableWhileStatusIs extends StatefulWidget {
   const _TappableWhileStatusIs(
       this.status, {
         Key key,
         this.controller,
         this.child,
       }) : super(key: key);

   final AnimationController controller;
   final AnimationStatus status;
   final Widget child;

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

 class _TappableWhileStatusIsState extends State<_TappableWhileStatusIs> {
   bool _active;

   @override
   void initState() {
     super.initState();
     widget.controller.addStatusListener(_handleStatusChange);
     _active = widget.controller.status == widget.status;
   }

   @override
   void dispose() {
     widget.controller.removeStatusListener(_handleStatusChange);
     super.dispose();
   }

   void _handleStatusChange(AnimationStatus status) {
     final bool value = widget.controller.status == widget.status;
     if (_active != value) {
       setState(() {
         _active = value;
       });
     }
   }

   @override
   Widget build(BuildContext context) {
     Widget child = AbsorbPointer(
       absorbing: !_active,
       child: widget.child,
     );

     if (!_active) {
       child = FocusScope(
         canRequestFocus: false,
         debugLabel: '$_TappableWhileStatusIs',
         child: child,
       );
     }
     return child;
   }
 }

 class _FrontLayer extends StatelessWidget {
   const _FrontLayer({
     Key key,
     this.onTap,
     this.child,
   }) : super(key: key);

   final VoidCallback onTap;
   final Widget child;

   @override
   Widget build(BuildContext context) {
     return Material(
       elevation: 16.0,
       shape: const BeveledRectangleBorder(
         borderRadius: BorderRadius.only(topLeft: Radius.circular(46.0)),
       ),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,
         children: <Widget>[
           GestureDetector(
             behavior: HitTestBehavior.opaque,
             onTap: onTap,
             child: Container(
               height: 40.0,
               alignment: AlignmentDirectional.centerStart,
             ),
           ),
           Expanded(
             child: child,
           ),
         ],
       ),
     );
   }
 }

 class _BackdropTitle extends AnimatedWidget {
   const _BackdropTitle({
     Key key,
     Listenable listenable,
     this.onPress,
     @required this.frontTitle,
     @required this.backTitle,
   }) : assert(frontTitle != null),
        assert(backTitle != null),
        super(key: key, listenable: listenable);

   final Function onPress;
   final Widget frontTitle;
   final Widget backTitle;

   @override
   Widget build(BuildContext context) {
     final Animation<double> animation = CurvedAnimation(
       parent: listenable,
       curve: const Interval(0.0, 0.78),
     );

     return DefaultTextStyle(
       style: Theme.of(context).primaryTextTheme.title,
       softWrap: false,
       overflow: TextOverflow.ellipsis,
       child: Row(children: <Widget>[
         // branded icon
         SizedBox(
           width: 72.0,
           child: IconButton(
             padding: const EdgeInsets.only(right: 8.0),
             onPressed: onPress,
             icon: Stack(children: <Widget>[
               Opacity(
                 opacity: animation.value,
                 child: const ImageIcon(AssetImage('packages/shrine_images/slanted_menu.png')),
               ),
               FractionalTranslation(
                 translation: Tween<Offset>(
                   begin: Offset.zero,
                   end: const Offset(1.0, 0.0),
                 ).evaluate(animation),
                 child: const ImageIcon(AssetImage('packages/shrine_images/diamond.png')),
               ),
             ]),
           ),
         ),
         // Here, we do a custom cross fade between backTitle and frontTitle.
         // This makes a smooth animation between the two texts.
         Stack(
           children: <Widget>[
             Opacity(
               opacity: CurvedAnimation(
                 parent: ReverseAnimation(animation),
                 curve: const Interval(0.5, 1.0),
               ).value,
               child: FractionalTranslation(
                 translation: Tween<Offset>(
                   begin: Offset.zero,
                   end: const Offset(0.5, 0.0),
                 ).evaluate(animation),
                 child: backTitle,
               ),
             ),
             Opacity(
               opacity: CurvedAnimation(
                 parent: animation,
                 curve: const Interval(0.5, 1.0),
               ).value,
               child: FractionalTranslation(
                 translation: Tween<Offset>(
                   begin: const Offset(-0.25, 0.0),
                   end: Offset.zero,
                 ).evaluate(animation),
                 child: frontTitle,
               ),
             ),
           ],
         ),
       ]),
     );
   }
 }

 /// Builds a Backdrop.
 ///
 /// A Backdrop widget has two layers, front and back. The front layer is shown
 /// by default, and slides down to show the back layer, from which a user
 /// can make a selection. The user can also configure the titles for when the
 /// front or back layer is showing.
 class Backdrop extends StatefulWidget {
   const Backdrop({
     @required this.frontLayer,
     @required this.backLayer,
     @required this.frontTitle,
     @required this.backTitle,
     @required this.controller,
   }) : assert(frontLayer != null),
        assert(backLayer != null),
        assert(frontTitle != null),
        assert(backTitle != null),
        assert(controller != null);

   final Widget frontLayer;
   final Widget backLayer;
   final Widget frontTitle;
   final Widget backTitle;
   final AnimationController controller;

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

 class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin {
   final GlobalKey _backdropKey = GlobalKey(debugLabel: 'Backdrop');
   AnimationController _controller;
   Animation<RelativeRect> _layerAnimation;

   @override
   void initState() {
     super.initState();
     _controller = widget.controller;
   }

   @override
   void dispose() {
     _controller.dispose();
     super.dispose();
   }

   bool get _frontLayerVisible {
     final AnimationStatus status = _controller.status;
     return status == AnimationStatus.completed || status == AnimationStatus.forward;
   }

   void _toggleBackdropLayerVisibility() {
     // Call setState here to update layerAnimation if that's necessary
     setState(() {
       _frontLayerVisible ? _controller.reverse() : _controller.forward();
     });
   }

   // _layerAnimation animates the front layer between open and close.
   // _getLayerAnimation adjusts the values in the TweenSequence so the
   // curve and timing are correct in both directions.
   Animation<RelativeRect> _getLayerAnimation(Size layerSize, double layerTop) {
     Curve firstCurve; // Curve for first TweenSequenceItem
     Curve secondCurve; // Curve for second TweenSequenceItem
     double firstWeight; // Weight of first TweenSequenceItem
     double secondWeight; // Weight of second TweenSequenceItem
     Animation<double> animation; // Animation on which TweenSequence runs

     if (_frontLayerVisible) {
       firstCurve = _kAccelerateCurve;
       secondCurve = _kDecelerateCurve;
       firstWeight = _kPeakVelocityTime;
       secondWeight = 1.0 - _kPeakVelocityTime;
       animation = CurvedAnimation(
         parent: _controller.view,
         curve: const Interval(0.0, 0.78),
       );
     } else {
       // These values are only used when the controller runs from t=1.0 to t=0.0
       firstCurve = _kDecelerateCurve.flipped;
       secondCurve = _kAccelerateCurve.flipped;
       firstWeight = 1.0 - _kPeakVelocityTime;
       secondWeight = _kPeakVelocityTime;
       animation = _controller.view;
     }

     return TweenSequence<RelativeRect>(
       <TweenSequenceItem<RelativeRect>>[
         TweenSequenceItem<RelativeRect>(
           tween: RelativeRectTween(
             begin: RelativeRect.fromLTRB(
               0.0,
               layerTop,
               0.0,
               layerTop - layerSize.height,
             ),
             end: RelativeRect.fromLTRB(
               0.0,
               layerTop * _kPeakVelocityProgress,
               0.0,
               (layerTop - layerSize.height) * _kPeakVelocityProgress,
             ),
           ).chain(CurveTween(curve: firstCurve)),
           weight: firstWeight,
         ),
         TweenSequenceItem<RelativeRect>(
           tween: RelativeRectTween(
             begin: RelativeRect.fromLTRB(
               0.0,
               layerTop * _kPeakVelocityProgress,
               0.0,
               (layerTop - layerSize.height) * _kPeakVelocityProgress,
             ),
             end: RelativeRect.fill,
           ).chain(CurveTween(curve: secondCurve)),
           weight: secondWeight,
         ),
       ],
     ).animate(animation);
   }

   Widget _buildStack(BuildContext context, BoxConstraints constraints) {
     const double layerTitleHeight = 48.0;
     final Size layerSize = constraints.biggest;
     final double layerTop = layerSize.height - layerTitleHeight;

     _layerAnimation = _getLayerAnimation(layerSize, layerTop);

     return Stack(
       key: _backdropKey,
       children: <Widget>[
         _TappableWhileStatusIs(
           AnimationStatus.dismissed,
           controller: _controller,
           child: widget.backLayer,
         ),
         PositionedTransition(
           rect: _layerAnimation,
           child: _FrontLayer(
             onTap: _toggleBackdropLayerVisibility,
             child: _TappableWhileStatusIs(
               AnimationStatus.completed,
               controller: _controller,
               child: widget.frontLayer,
             ),
           ),
         ),
       ],
     );
   }

   @override
   Widget build(BuildContext context) {
     final AppBar appBar = AppBar(
       brightness: Brightness.light,
       elevation: 0.0,
       titleSpacing: 0.0,
       title: _BackdropTitle(
         listenable: _controller.view,
         onPress: _toggleBackdropLayerVisibility,
         frontTitle: widget.frontTitle,
         backTitle: widget.backTitle,
       ),
       actions: <Widget>[
         IconButton(
           icon: const Icon(Icons.search, semanticLabel: 'login'),
           onPressed: () {
             Navigator.push<void>(
               context,
               MaterialPageRoute<void>(builder: (BuildContext context) => LoginPage()),
             );
           },
         ),
         IconButton(
           icon: const Icon(Icons.tune, semanticLabel: 'login'),
           onPressed: () {
             Navigator.push<void>(
               context,
               MaterialPageRoute<void>(builder: (BuildContext context) => LoginPage()),
             );
           },
         ),
       ],
     );
     return Scaffold(
       appBar: appBar,
       body: LayoutBuilder(
         builder: _buildStack,
       ),
     );
   }
 }
	// 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/material.dart';
	import 'package:meta/meta.dart';

	import 'package:flutter_gallery/demo/shrine/login.dart';

	const Cubic _kAccelerateCurve = Cubic(0.548, 0.0, 0.757, 0.464);
	const Cubic _kDecelerateCurve = Cubic(0.23, 0.94, 0.41, 1.0);
	const double _kPeakVelocityTime = 0.248210;
	const double _kPeakVelocityProgress = 0.379146;

	class _TappableWhileStatusIs extends StatefulWidget {
	const _TappableWhileStatusIs(
	this.status, {
	Key key,
	this.controller,
	this.child,
	}) : super(key: key);

	final AnimationController controller;
	final AnimationStatus status;
	final Widget child;

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

	class _TappableWhileStatusIsState extends State<_TappableWhileStatusIs> {
	bool _active;

	@override
	void initState() {
	super.initState();
	widget.controller.addStatusListener(_handleStatusChange);
	_active = widget.controller.status == widget.status;
	}

	@override
	void dispose() {
	widget.controller.removeStatusListener(_handleStatusChange);
	super.dispose();
	}

	void _handleStatusChange(AnimationStatus status) {
	final bool value = widget.controller.status == widget.status;
	if (_active != value) {
	setState(() {
	_active = value;
	});
	}
	}

	@override
	Widget build(BuildContext context) {
	Widget child = AbsorbPointer(
	absorbing: !_active,
	child: widget.child,
	);

	if (!_active) {
	child = FocusScope(
	canRequestFocus: false,
	debugLabel: '$_TappableWhileStatusIs',
	child: child,
	);
	}
	return child;
	}
	}

	class _FrontLayer extends StatelessWidget {
	const _FrontLayer({
	Key key,
	this.onTap,
	this.child,
	}) : super(key: key);

	final VoidCallback onTap;
	final Widget child;

	@override
	Widget build(BuildContext context) {
	return Material(
	elevation: 16.0,
	shape: const BeveledRectangleBorder(
	borderRadius: BorderRadius.only(topLeft: Radius.circular(46.0)),
	),
	child: Column(
	crossAxisAlignment: CrossAxisAlignment.stretch,
	children: <Widget>[
	GestureDetector(
	behavior: HitTestBehavior.opaque,
	onTap: onTap,
	child: Container(
	height: 40.0,
	alignment: AlignmentDirectional.centerStart,
	),
	),
	Expanded(
	child: child,
	),
	],
	),
	);
	}
	}

	class _BackdropTitle extends AnimatedWidget {
	const _BackdropTitle({
	Key key,
	Listenable listenable,
	this.onPress,
	@required this.frontTitle,
	@required this.backTitle,
	}) : assert(frontTitle != null),
	assert(backTitle != null),
	super(key: key, listenable: listenable);

	final Function onPress;
	final Widget frontTitle;
	final Widget backTitle;

	@override
	Widget build(BuildContext context) {
	final Animation<double> animation = CurvedAnimation(
	parent: listenable,
	curve: const Interval(0.0, 0.78),
	);

	return DefaultTextStyle(
	style: Theme.of(context).primaryTextTheme.title,
	softWrap: false,
	overflow: TextOverflow.ellipsis,
	child: Row(children: <Widget>[
	// branded icon
	SizedBox(
	width: 72.0,
	child: IconButton(
	padding: const EdgeInsets.only(right: 8.0),
	onPressed: onPress,
	icon: Stack(children: <Widget>[
	Opacity(
	opacity: animation.value,
	child: const ImageIcon(AssetImage('packages/shrine_images/slanted_menu.png')),
	),
	FractionalTranslation(
	translation: Tween<Offset>(
	begin: Offset.zero,
	end: const Offset(1.0, 0.0),
	).evaluate(animation),
	child: const ImageIcon(AssetImage('packages/shrine_images/diamond.png')),
	),
	]),
	),
	),
	// Here, we do a custom cross fade between backTitle and frontTitle.
	// This makes a smooth animation between the two texts.
	Stack(
	children: <Widget>[
	Opacity(
	opacity: CurvedAnimation(
	parent: ReverseAnimation(animation),
	curve: const Interval(0.5, 1.0),
	).value,
	child: FractionalTranslation(
	translation: Tween<Offset>(
	begin: Offset.zero,
	end: const Offset(0.5, 0.0),
	).evaluate(animation),
	child: backTitle,
	),
	),
	Opacity(
	opacity: CurvedAnimation(
	parent: animation,
	curve: const Interval(0.5, 1.0),
	).value,
	child: FractionalTranslation(
	translation: Tween<Offset>(
	begin: const Offset(-0.25, 0.0),
	end: Offset.zero,
	).evaluate(animation),
	child: frontTitle,
	),
	),
	],
	),
	]),
	);
	}
	}

	/// Builds a Backdrop.
	///
	/// A Backdrop widget has two layers, front and back. The front layer is shown
	/// by default, and slides down to show the back layer, from which a user
	/// can make a selection. The user can also configure the titles for when the
	/// front or back layer is showing.
	class Backdrop extends StatefulWidget {
	const Backdrop({
	@required this.frontLayer,
	@required this.backLayer,
	@required this.frontTitle,
	@required this.backTitle,
	@required this.controller,
	}) : assert(frontLayer != null),
	assert(backLayer != null),
	assert(frontTitle != null),
	assert(backTitle != null),
	assert(controller != null);

	final Widget frontLayer;
	final Widget backLayer;
	final Widget frontTitle;
	final Widget backTitle;
	final AnimationController controller;

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

	class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin {
	final GlobalKey _backdropKey = GlobalKey(debugLabel: 'Backdrop');
	AnimationController _controller;
	Animation<RelativeRect> _layerAnimation;

	@override
	void initState() {
	super.initState();
	_controller = widget.controller;
	}

	@override
	void dispose() {
	_controller.dispose();
	super.dispose();
	}

	bool get _frontLayerVisible {
	final AnimationStatus status = _controller.status;
	return status == AnimationStatus.completed \|\| status == AnimationStatus.forward;
	}

	void _toggleBackdropLayerVisibility() {
	// Call setState here to update layerAnimation if that's necessary
	setState(() {
	_frontLayerVisible ? _controller.reverse() : _controller.forward();
	});
	}

	// _layerAnimation animates the front layer between open and close.
	// _getLayerAnimation adjusts the values in the TweenSequence so the
	// curve and timing are correct in both directions.
	Animation<RelativeRect> _getLayerAnimation(Size layerSize, double layerTop) {
	Curve firstCurve; // Curve for first TweenSequenceItem
	Curve secondCurve; // Curve for second TweenSequenceItem
	double firstWeight; // Weight of first TweenSequenceItem
	double secondWeight; // Weight of second TweenSequenceItem
	Animation<double> animation; // Animation on which TweenSequence runs

	if (_frontLayerVisible) {
	firstCurve = _kAccelerateCurve;
	secondCurve = _kDecelerateCurve;
	firstWeight = _kPeakVelocityTime;
	secondWeight = 1.0 - _kPeakVelocityTime;
	animation = CurvedAnimation(
	parent: _controller.view,
	curve: const Interval(0.0, 0.78),
	);
	} else {
	// These values are only used when the controller runs from t=1.0 to t=0.0
	firstCurve = _kDecelerateCurve.flipped;
	secondCurve = _kAccelerateCurve.flipped;
	firstWeight = 1.0 - _kPeakVelocityTime;
	secondWeight = _kPeakVelocityTime;
	animation = _controller.view;
	}

	return TweenSequence<RelativeRect>(
	<TweenSequenceItem<RelativeRect>>[
	TweenSequenceItem<RelativeRect>(
	tween: RelativeRectTween(
	begin: RelativeRect.fromLTRB(
	0.0,
	layerTop,
	0.0,
	layerTop - layerSize.height,
	),
	end: RelativeRect.fromLTRB(
	0.0,
	layerTop * _kPeakVelocityProgress,
	0.0,
	(layerTop - layerSize.height) * _kPeakVelocityProgress,
	),
	).chain(CurveTween(curve: firstCurve)),
	weight: firstWeight,
	),
	TweenSequenceItem<RelativeRect>(
	tween: RelativeRectTween(
	begin: RelativeRect.fromLTRB(
	0.0,
	layerTop * _kPeakVelocityProgress,
	0.0,
	(layerTop - layerSize.height) * _kPeakVelocityProgress,
	),
	end: RelativeRect.fill,
	).chain(CurveTween(curve: secondCurve)),
	weight: secondWeight,
	),
	],
	).animate(animation);
	}

	Widget _buildStack(BuildContext context, BoxConstraints constraints) {
	const double layerTitleHeight = 48.0;
	final Size layerSize = constraints.biggest;
	final double layerTop = layerSize.height - layerTitleHeight;

	_layerAnimation = _getLayerAnimation(layerSize, layerTop);

	return Stack(
	key: _backdropKey,
	children: <Widget>[
	_TappableWhileStatusIs(
	AnimationStatus.dismissed,
	controller: _controller,
	child: widget.backLayer,
	),
	PositionedTransition(
	rect: _layerAnimation,
	child: _FrontLayer(
	onTap: _toggleBackdropLayerVisibility,
	child: _TappableWhileStatusIs(
	AnimationStatus.completed,
	controller: _controller,
	child: widget.frontLayer,
	),
	),
	),
	],
	);
	}

	@override
	Widget build(BuildContext context) {
	final AppBar appBar = AppBar(
	brightness: Brightness.light,
	elevation: 0.0,
	titleSpacing: 0.0,
	title: _BackdropTitle(
	listenable: _controller.view,
	onPress: _toggleBackdropLayerVisibility,
	frontTitle: widget.frontTitle,
	backTitle: widget.backTitle,
	),
	actions: <Widget>[
	IconButton(
	icon: const Icon(Icons.search, semanticLabel: 'login'),
	onPressed: () {
	Navigator.push<void>(
	context,
	MaterialPageRoute<void>(builder: (BuildContext context) => LoginPage()),
	);
	},
	),
	IconButton(
	icon: const Icon(Icons.tune, semanticLabel: 'login'),
	onPressed: () {
	Navigator.push<void>(
	context,
	MaterialPageRoute<void>(builder: (BuildContext context) => LoginPage()),
	);
	},
	),
	],
	);
	return Scaffold(
	appBar: appBar,
	body: LayoutBuilder(
	builder: _buildStack,
	),
	);
	}
	}