dev/manual_tests/lib/actions.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 'dart:collection';
 import 'dart:io';

 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';

 void main() {
   runApp(const MaterialApp(
     title: 'Actions Demo',
     home: FocusDemo(),
   ));
 }

 /// A class that can hold invocation information that an [UndoableAction] can
 /// use to undo/redo itself.
 ///
 /// Instances of this class are returned from [UndoableAction]s and placed on
 /// the undo stack when they are invoked.
 class Memento extends Object with Diagnosticable {
   const Memento({
     required this.name,
     required this.undo,
     required this.redo,
   });

   /// Returns true if this Memento can be used to undo.
   ///
   /// Subclasses could override to provide their own conditions when a command is
   /// undoable.
   bool get canUndo => true;

   /// Returns true if this Memento can be used to redo.
   ///
   /// Subclasses could override to provide their own conditions when a command is
   /// redoable.
   bool get canRedo => true;

   final String name;
   final VoidCallback undo;
   final ValueGetter<Memento> redo;

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     properties.add(StringProperty('name', name));
   }
 }

 /// Undoable Actions

 /// An [ActionDispatcher] subclass that manages the invocation of undoable
 /// actions.
 class UndoableActionDispatcher extends ActionDispatcher implements Listenable {
   /// Constructs a new [UndoableActionDispatcher].
   ///
   /// The [maxUndoLevels] argument must not be null.
   UndoableActionDispatcher({
     int maxUndoLevels = _defaultMaxUndoLevels,
   })  : _maxUndoLevels = maxUndoLevels;

   // A stack of actions that have been performed. The most recent action
   // performed is at the end of the list.
   final DoubleLinkedQueue<Memento> _completedActions = DoubleLinkedQueue<Memento>();
   // A stack of actions that can be redone. The most recent action performed is
   // at the end of the list.
   final List<Memento> _undoneActions = <Memento>[];

   static const int _defaultMaxUndoLevels = 1000;

   /// The maximum number of undo levels allowed.
   ///
   /// If this value is set to a value smaller than the number of completed
   /// actions, then the stack of completed actions is truncated to only include
   /// the last [maxUndoLevels] actions.
   int get maxUndoLevels => _maxUndoLevels;
   int _maxUndoLevels;
   set maxUndoLevels(int value) {
     _maxUndoLevels = value;
     _pruneActions();
   }

   final Set<VoidCallback> _listeners = <VoidCallback>{};

   @override
   void addListener(VoidCallback listener) {
     _listeners.add(listener);
   }

   @override
   void removeListener(VoidCallback listener) {
     _listeners.remove(listener);
   }

   /// Notifies listeners that the [ActionDispatcher] has changed state.
   ///
   /// May only be called by subclasses.
   @protected
   void notifyListeners() {
     for (final VoidCallback callback in _listeners) {
       callback();
     }
   }

   @override
   Object? invokeAction(Action<Intent> action, Intent intent, [BuildContext? context]) {
     final Object? result = super.invokeAction(action, intent, context);
     print('Invoking ${action is UndoableAction ? 'undoable ' : ''}$intent as $action: $this ');
     if (action is UndoableAction) {
       _completedActions.addLast(result! as Memento);
       _undoneActions.clear();
       _pruneActions();
       notifyListeners();
     }
     return result;
   }

   // Enforces undo level limit.
   void _pruneActions() {
     while (_completedActions.length > _maxUndoLevels) {
       _completedActions.removeFirst();
     }
   }

   /// Returns true if there is an action on the stack that can be undone.
   bool get canUndo {
     if (_completedActions.isNotEmpty) {
       return _completedActions.first.canUndo;
     }
     return false;
   }

   /// Returns true if an action that has been undone can be re-invoked.
   bool get canRedo {
     if (_undoneActions.isNotEmpty) {
       return _undoneActions.first.canRedo;
     }
     return false;
   }

   /// Undoes the last action executed if possible.
   ///
   /// Returns true if the action was successfully undone.
   bool undo() {
     print('Undoing. $this');
     if (!canUndo) {
       return false;
     }
     final Memento memento = _completedActions.removeLast();
     memento.undo();
     _undoneActions.add(memento);
     notifyListeners();
     return true;
   }

   /// Re-invokes a previously undone action, if possible.
   ///
   /// Returns true if the action was successfully invoked.
   bool redo() {
     print('Redoing. $this');
     if (!canRedo) {
       return false;
     }
     final Memento memento = _undoneActions.removeLast();
     final Memento replacement = memento.redo();
     _completedActions.add(replacement);
     _pruneActions();
     notifyListeners();
     return true;
   }

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     properties.add(IntProperty('undoable items', _completedActions.length));
     properties.add(IntProperty('redoable items', _undoneActions.length));
     properties.add(IterableProperty<Memento>('undo stack', _completedActions));
     properties.add(IterableProperty<Memento>('redo stack', _undoneActions));
   }
 }

 class UndoIntent extends Intent {
   const UndoIntent();
 }

 class UndoAction extends Action<UndoIntent> {
   @override
   bool isEnabled(UndoIntent intent) {
     final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
     if (buildContext == null) {
       return false;
     }
     final UndoableActionDispatcher manager = Actions.of(buildContext) as UndoableActionDispatcher;
     return manager.canUndo;
   }

   @override
   void invoke(UndoIntent intent) {
     final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
     if (buildContext == null) {
       return;
     }
     final UndoableActionDispatcher manager = Actions.of(primaryFocus?.context ?? FocusDemo.appKey.currentContext!) as UndoableActionDispatcher;
     manager.undo();
   }
 }

 class RedoIntent extends Intent {
   const RedoIntent();
 }

 class RedoAction extends Action<RedoIntent> {
   @override
   bool isEnabled(RedoIntent intent) {
     final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
     if (buildContext == null) {
       return false;
     }
     final UndoableActionDispatcher manager = Actions.of(buildContext) as UndoableActionDispatcher;
     return manager.canRedo;
   }

   @override
   RedoAction invoke(RedoIntent intent) {
     final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
     if (buildContext == null) {
       return this;
     }
     final UndoableActionDispatcher manager = Actions.of(buildContext) as UndoableActionDispatcher;
     manager.redo();
     return this;
   }
 }

 /// An action that can be undone.
 abstract class UndoableAction<T extends Intent> extends Action<T> {
   /// The [Intent] this action was originally invoked with.
   Intent? get invocationIntent => _invocationTag;
   Intent? _invocationTag;

   @protected
   set invocationIntent(Intent? value) => _invocationTag = value;

   @override
   @mustCallSuper
   void invoke(T intent) {
     invocationIntent = intent;
   }
 }

 class UndoableFocusActionBase<T extends Intent> extends UndoableAction<T> {
   @override
   @mustCallSuper
   Memento invoke(T intent) {
     super.invoke(intent);
     final FocusNode? previousFocus = primaryFocus;
     return Memento(name: previousFocus!.debugLabel!, undo: () {
       previousFocus.requestFocus();
     }, redo: () {
       return invoke(intent);
     });
   }
 }

 class UndoableRequestFocusAction extends UndoableFocusActionBase<RequestFocusIntent> {
   @override
   Memento invoke(RequestFocusIntent intent) {
     final Memento memento = super.invoke(intent);
     intent.focusNode.requestFocus();
     return memento;
   }
 }

 /// Actions for manipulating focus.
 class UndoableNextFocusAction extends UndoableFocusActionBase<NextFocusIntent> {
   @override
   Memento invoke(NextFocusIntent intent) {
     final Memento memento = super.invoke(intent);
     primaryFocus?.nextFocus();
     return memento;
   }
 }

 class UndoablePreviousFocusAction extends UndoableFocusActionBase<PreviousFocusIntent> {
   @override
   Memento invoke(PreviousFocusIntent intent) {
     final Memento memento = super.invoke(intent);
     primaryFocus?.previousFocus();
     return memento;
   }
 }

 class UndoableDirectionalFocusAction extends UndoableFocusActionBase<DirectionalFocusIntent> {
   TraversalDirection? direction;

   @override
   Memento invoke(DirectionalFocusIntent intent) {
     final Memento memento = super.invoke(intent);
     primaryFocus?.focusInDirection(intent.direction);
     return memento;
   }
 }

 /// A button class that takes focus when clicked.
 class DemoButton extends StatefulWidget {
   const DemoButton({super.key, required this.name});

   final String name;

   @override
   State<DemoButton> createState() => _DemoButtonState();
 }

 class _DemoButtonState extends State<DemoButton> {
   late final FocusNode _focusNode = FocusNode(debugLabel: widget.name);
   final GlobalKey _nameKey = GlobalKey();

   void _handleOnPressed() {
     print('Button ${widget.name} pressed.');
     setState(() {
       Actions.invoke(_nameKey.currentContext!, RequestFocusIntent(_focusNode));
     });
   }

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

   @override
   Widget build(BuildContext context) {
     return TextButton(
       focusNode: _focusNode,
       style: ButtonStyle(
         foregroundColor: const MaterialStatePropertyAll<Color>(Colors.black),
         overlayColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
           if (states.contains(MaterialState.focused)) {
             return Colors.red;
           }
           if (states.contains(MaterialState.hovered)) {
             return Colors.blue;
           }
           return Colors.transparent;
         }),
       ),
       onPressed: () => _handleOnPressed(),
       child: Text(widget.name, key: _nameKey),
     );
   }
 }

 class FocusDemo extends StatefulWidget {
   const FocusDemo({super.key});

   static GlobalKey appKey = GlobalKey();

   @override
   State<FocusDemo> createState() => _FocusDemoState();
 }

 class _FocusDemoState extends State<FocusDemo> {
   final FocusNode outlineFocus = FocusNode(debugLabel: 'Demo Focus Node');
   late final UndoableActionDispatcher dispatcher = UndoableActionDispatcher();
   bool canUndo = false;
   bool canRedo = false;

   @override
   void initState() {
     super.initState();
     canUndo = dispatcher.canUndo;
     canRedo = dispatcher.canRedo;
     dispatcher.addListener(_handleUndoStateChange);
   }

   void _handleUndoStateChange() {
     if (dispatcher.canUndo != canUndo) {
       setState(() {
         canUndo = dispatcher.canUndo;
       });
     }
     if (dispatcher.canRedo != canRedo) {
       setState(() {
         canRedo = dispatcher.canRedo;
       });
     }
   }

   @override
   void dispose() {
     dispatcher.removeListener(_handleUndoStateChange);
     outlineFocus.dispose();
     super.dispose();
   }

   @override
   Widget build(BuildContext context) {
     final TextTheme textTheme = Theme.of(context).textTheme;
     return Actions(
       dispatcher: dispatcher,
       actions: <Type, Action<Intent>>{
         RequestFocusIntent: UndoableRequestFocusAction(),
         NextFocusIntent: UndoableNextFocusAction(),
         PreviousFocusIntent: UndoablePreviousFocusAction(),
         DirectionalFocusIntent: UndoableDirectionalFocusAction(),
         UndoIntent: UndoAction(),
         RedoIntent: RedoAction(),
       },
       child: FocusTraversalGroup(
         policy: ReadingOrderTraversalPolicy(),
         child: Shortcuts(
           shortcuts: <ShortcutActivator, Intent>{
             SingleActivator(LogicalKeyboardKey.keyZ, meta: Platform.isMacOS, control: !Platform.isMacOS, shift: true): const RedoIntent(),
             SingleActivator(LogicalKeyboardKey.keyZ, meta: Platform.isMacOS, control: !Platform.isMacOS): const UndoIntent(),
           },
           child: FocusScope(
             key: FocusDemo.appKey,
             debugLabel: 'Scope',
             autofocus: true,
             child: DefaultTextStyle(
               style: textTheme.headlineMedium!,
               child: Scaffold(
                 appBar: AppBar(
                   title: const Text('Actions Demo'),
                 ),
                 body: Center(
                   child: Builder(builder: (BuildContext context) {
                     return Column(
                       mainAxisAlignment: MainAxisAlignment.center,
                       children: <Widget>[
                         Row(
                           mainAxisAlignment: MainAxisAlignment.center,
                           children: const <Widget>[
                             DemoButton(name: 'One'),
                             DemoButton(name: 'Two'),
                             DemoButton(name: 'Three'),
                           ],
                         ),
                         Row(
                           mainAxisAlignment: MainAxisAlignment.center,
                           children: const <Widget>[
                             DemoButton(name: 'Four'),
                             DemoButton(name: 'Five'),
                             DemoButton(name: 'Six'),
                           ],
                         ),
                         Row(
                           mainAxisAlignment: MainAxisAlignment.center,
                           children: const <Widget>[
                             DemoButton(name: 'Seven'),
                             DemoButton(name: 'Eight'),
                             DemoButton(name: 'Nine'),
                           ],
                         ),
                         Row(
                           mainAxisAlignment: MainAxisAlignment.center,
                           children: <Widget>[
                             Padding(
                               padding: const EdgeInsets.all(8.0),
                               child: ElevatedButton(
                                 onPressed: canUndo
                                     ? () {
                                         Actions.invoke(context, const UndoIntent());
                                       }
                                     : null,
                                 child: const Text('UNDO'),
                               ),
                             ),
                             Padding(
                               padding: const EdgeInsets.all(8.0),
                               child: ElevatedButton(
                                 onPressed: canRedo
                                     ? () {
                                         Actions.invoke(context, const RedoIntent());
                                       }
                                     : null,
                                 child: const Text('REDO'),
                               ),
                             ),
                           ],
                         ),
                       ],
                     );
                   }),
                 ),
               ),
             ),
           ),
         ),
       ),
     );
   }
 }
	// 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 'dart:collection';
	import 'dart:io';

	import 'package:flutter/foundation.dart';
	import 'package:flutter/material.dart';
	import 'package:flutter/services.dart';

	void main() {
	runApp(const MaterialApp(
	title: 'Actions Demo',
	home: FocusDemo(),
	));
	}

	/// A class that can hold invocation information that an [UndoableAction] can
	/// use to undo/redo itself.
	///
	/// Instances of this class are returned from [UndoableAction]s and placed on
	/// the undo stack when they are invoked.
	class Memento extends Object with Diagnosticable {
	const Memento({
	required this.name,
	required this.undo,
	required this.redo,
	});

	/// Returns true if this Memento can be used to undo.
	///
	/// Subclasses could override to provide their own conditions when a command is
	/// undoable.
	bool get canUndo => true;

	/// Returns true if this Memento can be used to redo.
	///
	/// Subclasses could override to provide their own conditions when a command is
	/// redoable.
	bool get canRedo => true;

	final String name;
	final VoidCallback undo;
	final ValueGetter<Memento> redo;

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder properties) {
	super.debugFillProperties(properties);
	properties.add(StringProperty('name', name));
	}
	}

	/// Undoable Actions

	/// An [ActionDispatcher] subclass that manages the invocation of undoable
	/// actions.
	class UndoableActionDispatcher extends ActionDispatcher implements Listenable {
	/// Constructs a new [UndoableActionDispatcher].
	///
	/// The [maxUndoLevels] argument must not be null.
	UndoableActionDispatcher({
	int maxUndoLevels = _defaultMaxUndoLevels,
	}) : _maxUndoLevels = maxUndoLevels;

	// A stack of actions that have been performed. The most recent action
	// performed is at the end of the list.
	final DoubleLinkedQueue<Memento> _completedActions = DoubleLinkedQueue<Memento>();
	// A stack of actions that can be redone. The most recent action performed is
	// at the end of the list.
	final List<Memento> _undoneActions = <Memento>[];

	static const int _defaultMaxUndoLevels = 1000;

	/// The maximum number of undo levels allowed.
	///
	/// If this value is set to a value smaller than the number of completed
	/// actions, then the stack of completed actions is truncated to only include
	/// the last [maxUndoLevels] actions.
	int get maxUndoLevels => _maxUndoLevels;
	int _maxUndoLevels;
	set maxUndoLevels(int value) {
	_maxUndoLevels = value;
	_pruneActions();
	}

	final Set<VoidCallback> _listeners = <VoidCallback>{};

	@override
	void addListener(VoidCallback listener) {
	_listeners.add(listener);
	}

	@override
	void removeListener(VoidCallback listener) {
	_listeners.remove(listener);
	}

	/// Notifies listeners that the [ActionDispatcher] has changed state.
	///
	/// May only be called by subclasses.
	@protected
	void notifyListeners() {
	for (final VoidCallback callback in _listeners) {
	callback();
	}
	}

	@override
	Object? invokeAction(Action<Intent> action, Intent intent, [BuildContext? context]) {
	final Object? result = super.invokeAction(action, intent, context);
	print('Invoking ${action is UndoableAction ? 'undoable ' : ''}$intent as $action: $this ');
	if (action is UndoableAction) {
	_completedActions.addLast(result! as Memento);
	_undoneActions.clear();
	_pruneActions();
	notifyListeners();
	}
	return result;
	}

	// Enforces undo level limit.
	void _pruneActions() {
	while (_completedActions.length > _maxUndoLevels) {
	_completedActions.removeFirst();
	}
	}

	/// Returns true if there is an action on the stack that can be undone.
	bool get canUndo {
	if (_completedActions.isNotEmpty) {
	return _completedActions.first.canUndo;
	}
	return false;
	}

	/// Returns true if an action that has been undone can be re-invoked.
	bool get canRedo {
	if (_undoneActions.isNotEmpty) {
	return _undoneActions.first.canRedo;
	}
	return false;
	}

	/// Undoes the last action executed if possible.
	///
	/// Returns true if the action was successfully undone.
	bool undo() {
	print('Undoing. $this');
	if (!canUndo) {
	return false;
	}
	final Memento memento = _completedActions.removeLast();
	memento.undo();
	_undoneActions.add(memento);
	notifyListeners();
	return true;
	}

	/// Re-invokes a previously undone action, if possible.
	///
	/// Returns true if the action was successfully invoked.
	bool redo() {
	print('Redoing. $this');
	if (!canRedo) {
	return false;
	}
	final Memento memento = _undoneActions.removeLast();
	final Memento replacement = memento.redo();
	_completedActions.add(replacement);
	_pruneActions();
	notifyListeners();
	return true;
	}

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder properties) {
	super.debugFillProperties(properties);
	properties.add(IntProperty('undoable items', _completedActions.length));
	properties.add(IntProperty('redoable items', _undoneActions.length));
	properties.add(IterableProperty<Memento>('undo stack', _completedActions));
	properties.add(IterableProperty<Memento>('redo stack', _undoneActions));
	}
	}

	class UndoIntent extends Intent {
	const UndoIntent();
	}

	class UndoAction extends Action<UndoIntent> {
	@override
	bool isEnabled(UndoIntent intent) {
	final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
	if (buildContext == null) {
	return false;
	}
	final UndoableActionDispatcher manager = Actions.of(buildContext) as UndoableActionDispatcher;
	return manager.canUndo;
	}

	@override
	void invoke(UndoIntent intent) {
	final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
	if (buildContext == null) {
	return;
	}
	final UndoableActionDispatcher manager = Actions.of(primaryFocus?.context ?? FocusDemo.appKey.currentContext!) as UndoableActionDispatcher;
	manager.undo();
	}
	}

	class RedoIntent extends Intent {
	const RedoIntent();
	}

	class RedoAction extends Action<RedoIntent> {
	@override
	bool isEnabled(RedoIntent intent) {
	final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
	if (buildContext == null) {
	return false;
	}
	final UndoableActionDispatcher manager = Actions.of(buildContext) as UndoableActionDispatcher;
	return manager.canRedo;
	}

	@override
	RedoAction invoke(RedoIntent intent) {
	final BuildContext? buildContext = primaryFocus?.context ?? FocusDemo.appKey.currentContext;
	if (buildContext == null) {
	return this;
	}
	final UndoableActionDispatcher manager = Actions.of(buildContext) as UndoableActionDispatcher;
	manager.redo();
	return this;
	}
	}

	/// An action that can be undone.
	abstract class UndoableAction<T extends Intent> extends Action<T> {
	/// The [Intent] this action was originally invoked with.
	Intent? get invocationIntent => _invocationTag;
	Intent? _invocationTag;

	@protected
	set invocationIntent(Intent? value) => _invocationTag = value;

	@override
	@mustCallSuper
	void invoke(T intent) {
	invocationIntent = intent;
	}
	}

	class UndoableFocusActionBase<T extends Intent> extends UndoableAction<T> {
	@override
	@mustCallSuper
	Memento invoke(T intent) {
	super.invoke(intent);
	final FocusNode? previousFocus = primaryFocus;
	return Memento(name: previousFocus!.debugLabel!, undo: () {
	previousFocus.requestFocus();
	}, redo: () {
	return invoke(intent);
	});
	}
	}

	class UndoableRequestFocusAction extends UndoableFocusActionBase<RequestFocusIntent> {
	@override
	Memento invoke(RequestFocusIntent intent) {
	final Memento memento = super.invoke(intent);
	intent.focusNode.requestFocus();
	return memento;
	}
	}

	/// Actions for manipulating focus.
	class UndoableNextFocusAction extends UndoableFocusActionBase<NextFocusIntent> {
	@override
	Memento invoke(NextFocusIntent intent) {
	final Memento memento = super.invoke(intent);
	primaryFocus?.nextFocus();
	return memento;
	}
	}

	class UndoablePreviousFocusAction extends UndoableFocusActionBase<PreviousFocusIntent> {
	@override
	Memento invoke(PreviousFocusIntent intent) {
	final Memento memento = super.invoke(intent);
	primaryFocus?.previousFocus();
	return memento;
	}
	}

	class UndoableDirectionalFocusAction extends UndoableFocusActionBase<DirectionalFocusIntent> {
	TraversalDirection? direction;

	@override
	Memento invoke(DirectionalFocusIntent intent) {
	final Memento memento = super.invoke(intent);
	primaryFocus?.focusInDirection(intent.direction);
	return memento;
	}
	}

	/// A button class that takes focus when clicked.
	class DemoButton extends StatefulWidget {
	const DemoButton({super.key, required this.name});

	final String name;

	@override
	State<DemoButton> createState() => _DemoButtonState();
	}

	class _DemoButtonState extends State<DemoButton> {
	late final FocusNode _focusNode = FocusNode(debugLabel: widget.name);
	final GlobalKey _nameKey = GlobalKey();

	void _handleOnPressed() {
	print('Button ${widget.name} pressed.');
	setState(() {
	Actions.invoke(_nameKey.currentContext!, RequestFocusIntent(_focusNode));
	});
	}

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

	@override
	Widget build(BuildContext context) {
	return TextButton(
	focusNode: _focusNode,
	style: ButtonStyle(
	foregroundColor: const MaterialStatePropertyAll<Color>(Colors.black),
	overlayColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
	if (states.contains(MaterialState.focused)) {
	return Colors.red;
	}
	if (states.contains(MaterialState.hovered)) {
	return Colors.blue;
	}
	return Colors.transparent;
	}),
	),
	onPressed: () => _handleOnPressed(),
	child: Text(widget.name, key: _nameKey),
	);
	}
	}

	class FocusDemo extends StatefulWidget {
	const FocusDemo({super.key});

	static GlobalKey appKey = GlobalKey();

	@override
	State<FocusDemo> createState() => _FocusDemoState();
	}

	class _FocusDemoState extends State<FocusDemo> {
	final FocusNode outlineFocus = FocusNode(debugLabel: 'Demo Focus Node');
	late final UndoableActionDispatcher dispatcher = UndoableActionDispatcher();
	bool canUndo = false;
	bool canRedo = false;

	@override
	void initState() {
	super.initState();
	canUndo = dispatcher.canUndo;
	canRedo = dispatcher.canRedo;
	dispatcher.addListener(_handleUndoStateChange);
	}

	void _handleUndoStateChange() {
	if (dispatcher.canUndo != canUndo) {
	setState(() {
	canUndo = dispatcher.canUndo;
	});
	}
	if (dispatcher.canRedo != canRedo) {
	setState(() {
	canRedo = dispatcher.canRedo;
	});
	}
	}

	@override
	void dispose() {
	dispatcher.removeListener(_handleUndoStateChange);
	outlineFocus.dispose();
	super.dispose();
	}

	@override
	Widget build(BuildContext context) {
	final TextTheme textTheme = Theme.of(context).textTheme;
	return Actions(
	dispatcher: dispatcher,
	actions: <Type, Action<Intent>>{
	RequestFocusIntent: UndoableRequestFocusAction(),
	NextFocusIntent: UndoableNextFocusAction(),
	PreviousFocusIntent: UndoablePreviousFocusAction(),
	DirectionalFocusIntent: UndoableDirectionalFocusAction(),
	UndoIntent: UndoAction(),
	RedoIntent: RedoAction(),
	},
	child: FocusTraversalGroup(
	policy: ReadingOrderTraversalPolicy(),
	child: Shortcuts(
	shortcuts: <ShortcutActivator, Intent>{
	SingleActivator(LogicalKeyboardKey.keyZ, meta: Platform.isMacOS, control: !Platform.isMacOS, shift: true): const RedoIntent(),
	SingleActivator(LogicalKeyboardKey.keyZ, meta: Platform.isMacOS, control: !Platform.isMacOS): const UndoIntent(),
	},
	child: FocusScope(
	key: FocusDemo.appKey,
	debugLabel: 'Scope',
	autofocus: true,
	child: DefaultTextStyle(
	style: textTheme.headlineMedium!,
	child: Scaffold(
	appBar: AppBar(
	title: const Text('Actions Demo'),
	),
	body: Center(
	child: Builder(builder: (BuildContext context) {
	return Column(
	mainAxisAlignment: MainAxisAlignment.center,
	children: <Widget>[
	Row(
	mainAxisAlignment: MainAxisAlignment.center,
	children: const <Widget>[
	DemoButton(name: 'One'),
	DemoButton(name: 'Two'),
	DemoButton(name: 'Three'),
	],
	),
	Row(
	mainAxisAlignment: MainAxisAlignment.center,
	children: const <Widget>[
	DemoButton(name: 'Four'),
	DemoButton(name: 'Five'),
	DemoButton(name: 'Six'),
	],
	),
	Row(
	mainAxisAlignment: MainAxisAlignment.center,
	children: const <Widget>[
	DemoButton(name: 'Seven'),
	DemoButton(name: 'Eight'),
	DemoButton(name: 'Nine'),
	],
	),
	Row(
	mainAxisAlignment: MainAxisAlignment.center,
	children: <Widget>[
	Padding(
	padding: const EdgeInsets.all(8.0),
	child: ElevatedButton(
	onPressed: canUndo
	? () {
	Actions.invoke(context, const UndoIntent());
	}
	: null,
	child: const Text('UNDO'),
	),
	),
	Padding(
	padding: const EdgeInsets.all(8.0),
	child: ElevatedButton(
	onPressed: canRedo
	? () {
	Actions.invoke(context, const RedoIntent());
	}
	: null,
	child: const Text('REDO'),
	),
	),
	],
	),
	],
	);
	}),
	),
	),
	),
	),
	),
	),
	);
	}
	}