Added ExpansionTileController (#123298)

Added ExpansionTileController

examples/api/lib/material/expansion_tile/expansion_tile.1.dart

+// 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.
+
+// Flutter code sample for [ExpansionTile] and [ExpansionTileController]
+
+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(const ExpansionTileControllerApp());
+}
+
+class ExpansionTileControllerApp extends StatefulWidget {
+  const ExpansionTileControllerApp({ super.key });
+
+  @override
+  State<ExpansionTileControllerApp> createState() => _ExpansionTileControllerAppState();
+}
+
+class _ExpansionTileControllerAppState extends State<ExpansionTileControllerApp> {
+  final ExpansionTileController controller = ExpansionTileController();
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Flutter Code Sample for ExpansionTileController.',
+      theme: ThemeData(useMaterial3: true),
+      home: Scaffold(
+        appBar: AppBar(title: const Text('ExpansionTileController Example')),
+        body: Column(
+          children: <Widget>[
+            // A controller has been provided to the ExpansionTile because it's
+            // going to be accessed from a component that is not within the
+            // tile's BuildContext.
+            ExpansionTile(
+              controller: controller,
+              title: const Text('ExpansionTile with explicit controller.'),
+              children: <Widget>[
+                Container(
+                  alignment: Alignment.center,
+                  padding: const EdgeInsets.all(24),
+                  child: const Text('ExpansionTile Contents'),
+                ),
+              ],
+            ),
+            const SizedBox(height: 8),
+            ElevatedButton(
+              child: const Text('Expand/Collapse the Tile Above'),
+              onPressed: () {
+                if (controller.isExpanded) {
+                  controller.collapse();
+                } else {
+                  controller.expand();
+                }
+              },
+            ),
+            const SizedBox(height: 48),
+            // A controller has not been provided to the ExpansionTile because
+            // the automatically created one can be retrieved via the tile's BuildContext.
+            ExpansionTile(
+              title: const Text('ExpansionTile with implicit controller.'),
+              children: <Widget>[
+                Builder(
+                  builder: (BuildContext context) {
+                    return Container(
+                      padding: const EdgeInsets.all(24),
+                      alignment: Alignment.center,
+                      child: ElevatedButton(
+                        child: const Text('Collapse This Tile'),
+                        onPressed: () {
+                          return ExpansionTileController.of(context).collapse();
+                        },
+                      ),
+                    );
+                  },
+                ),
+              ],
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

examples/api/test/material/expansion_tile/expansion_tile.1_test.dart

+// 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_api_samples/material/expansion_tile/expansion_tile.1.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Test the basics of ExpansionTileControllerApp', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.ExpansionTileControllerApp(),
+    );
+
+    expect(find.text('ExpansionTile Contents'), findsNothing);
+    expect(find.text('Collapse This Tile'), findsNothing);
+
+    await tester.tap(find.text('Expand/Collapse the Tile Above'));
+    await tester.pumpAndSettle();
+    expect(find.text('ExpansionTile Contents'), findsOneWidget);
+    await tester.tap(find.text('Expand/Collapse the Tile Above'));
+    await tester.pumpAndSettle();
+    expect(find.text('ExpansionTile Contents'), findsNothing);
+
+    await tester.tap(find.text('ExpansionTile with implicit controller.'));
+    await tester.pumpAndSettle();
+    expect(find.text('Collapse This Tile'), findsOneWidget);
+    await tester.tap(find.text('Collapse This Tile'));
+    await tester.pumpAndSettle();
+    expect(find.text('Collapse This Tile'), findsNothing);
+  });
+}

packages/flutter/lib/src/material/expansion_tile.dart

@@ -15,6 +15,170 @@ import 'theme.dart';
 
 const Duration _kExpand = Duration(milliseconds: 200);
 
+/// Enables control over a single [ExpansionTile]'s expanded/collapsed state.
+///
+/// It can be useful to expand or collapse an [ExpansionTile]
+/// programatically, for example to reconfigure an existing expansion
+/// tile based on a system event. To do so, create an [ExpansionTile]
+/// with an [ExpansionTileController] that's owned by a stateful widget
+/// or look up the tile's automatically created [ExpansionTileController]
+/// with [ExpansionTileController.of]
+///
+/// The controller's [expand] and [collapse] methods cause the
+/// the [ExpansionTile] to rebuild, so they may not be called from
+/// a build method.
+class ExpansionTileController {
+  /// Create a controller to be used with [ExpansionTile.controller].
+  ExpansionTileController();
+
+  _ExpansionTileState? _state;
+
+  /// Whether the [ExpansionTile] built with this controller is in expanded state.
+  ///
+  /// This property doesn't take the animation into account. It reports `true`
+  /// even if the expansion animation is not completed.
+  ///
+  /// See also:
+  ///
+  ///  * [expand], which expands the [ExpansionTile].
+  ///  * [collapse], which collapses the [ExpansionTile].
+  ///  * [ExpansionTile.controller] to create an ExpansionTile with a controller.
+  bool get isExpanded {
+    assert(_state != null);
+    return _state!._isExpanded;
+  }
+
+  /// Expands the [ExpansionTile] that was built with this controller;
+  ///
+  /// Normally the tile is expanded automatically when the user taps on the header.
+  /// It is sometimes useful to trigger the expansion programmatically due
+  /// to external changes.
+  ///
+  /// If the tile is already in the expanded state (see [isExpanded]), calling
+  /// this method has no effect.
+  ///
+  /// Calling this method may cause the [ExpansionTile] to rebuild, so it may
+  /// not be called from a build method.
+  ///
+  /// Calling this method will trigger an [ExpansionTile.onExpansionChanged] callback.
+  ///
+  /// See also:
+  ///
+  ///  * [collapse], which collapses the tile.
+  ///  * [isExpanded] to check whether the tile is expanded.
+  ///  * [ExpansionTile.controller] to create an ExpansionTile with a controller.
+  void expand() {
+    assert(_state != null);
+    if (!isExpanded) {
+      _state!._toggleExpansion();
+    }
+  }
+
+  /// Collapses the [ExpansionTile] that was built with this controller.
+  ///
+  /// Normally the tile is collapsed automatically when the user taps on the header.
+  /// It can be useful sometimes to trigger the collapse programmatically due
+  /// to some external changes.
+  ///
+  /// If the tile is already in the collapsed state (see [isExpanded]), calling
+  /// this method has no effect.
+  ///
+  /// Calling this method may cause the [ExpansionTile] to rebuild, so it may
+  /// not be called from a build method.
+  ///
+  /// Calling this method will trigger an [ExpansionTile.onExpansionChanged] callback.
+  ///
+  /// See also:
+  ///
+  ///  * [expand], which expands the tile.
+  ///  * [isExpanded] to check whether the tile is expanded.
+  ///  * [ExpansionTile.controller] to create an ExpansionTile with a controller.
+  void collapse() {
+    assert(_state != null);
+    if (isExpanded) {
+      _state!._toggleExpansion();
+    }
+  }
+
+  /// Finds the [ExpansionTileController] for the closest [ExpansionTile] instance
+  /// that encloses the given context.
+  ///
+  /// If no [ExpansionTile] encloses the given context, calling this
+  /// method will cause an assert in debug mode, and throw an
+  /// exception in release mode.
+  ///
+  /// To return null if there is no [ExpansionTile] use [maybeOf] instead.
+  ///
+  /// {@tool dartpad}
+  /// Typical usage of the [ExpansionTileController.of] function is to call it from within the
+  /// `build` method of a descendant of an [ExpansionTile].
+  ///
+  /// When the [ExpansionTile] is actually created in the same `build`
+  /// function as the callback that refers to the controller, then the
+  /// `context` argument to the `build` function can't be used to find
+  /// the [ExpansionTileController] (since it's "above" the widget
+  /// being returned in the widget tree). In cases like that you can
+  /// add a [Builder] widget, which provides a new scope with a
+  /// [BuildContext] that is "under" the [ExpansionTile]:
+  ///
+  /// ** See code in examples/api/lib/material/expansion_tile/expansion_tile.1.dart **
+  /// {@end-tool}
+  ///
+  /// A more efficient solution is to split your build function into
+  /// several widgets. This introduces a new context from which you
+  /// can obtain the [ExpansionTileController]. With this approach you
+  /// would have an outer widget that creates the [ExpansionTile]
+  /// populated by instances of your new inner widgets, and then in
+  /// these inner widgets you would use [ExpansionTileController.of].
+  static ExpansionTileController of(BuildContext context) {
+    final _ExpansionTileState? result = context.findAncestorStateOfType<_ExpansionTileState>();
+    if (result != null) {
+      return result._tileController;
+    }
+    throw FlutterError.fromParts(<DiagnosticsNode>[
+      ErrorSummary(
+        'ExpansionTileController.of() called with a context that does not contain a ExpansionTile.',
+      ),
+      ErrorDescription(
+        'No ExpansionTile ancestor could be found starting from the context that was passed to ExpansionTileController.of(). '
+        'This usually happens when the context provided is from the same StatefulWidget as that '
+        'whose build function actually creates the ExpansionTile widget being sought.',
+      ),
+      ErrorHint(
+        'There are several ways to avoid this problem. The simplest is to use a Builder to get a '
+        'context that is "under" the ExpansionTile. For an example of this, please see the '
+        'documentation for ExpansionTileController.of():\n'
+        '  https://api.flutter.dev/flutter/material/ExpansionTile/of.html',
+      ),
+      ErrorHint(
+        'A more efficient solution is to split your build function into several widgets. This '
+        'introduces a new context from which you can obtain the ExpansionTile. In this solution, '
+        'you would have an outer widget that creates the ExpansionTile populated by instances of '
+        'your new inner widgets, and then in these inner widgets you would use ExpansionTileController.of().\n'
+        'An other solution is assign a GlobalKey to the ExpansionTile, '
+        'then use the key.currentState property to obtain the ExpansionTile rather than '
+        'using the ExpansionTileController.of() function.',
+      ),
+      context.describeElement('The context used was'),
+    ]);
+  }
+
+  /// Finds the [ExpansionTile] from the closest instance of this class that
+  /// encloses the given context and returns its [ExpansionTileController].
+  ///
+  /// If no [ExpansionTile] encloses the given context then return null.
+  /// To throw an exception instead, use [of] instead of this function.
+  ///
+  /// See also:
+  ///
+  ///  * [of], a similar function to this one that throws if no [ExpansionTile]
+  ///    encloses the given context. Also includes some sample code in its
+  ///    documentation.
+  static ExpansionTileController? maybeOf(BuildContext context) {
+    return context.findAncestorStateOfType<_ExpansionTileState>()?._tileController;
+  }
+}
+
 /// A single-line [ListTile] with an expansion arrow icon that expands or collapses
 /// the tile to reveal or hide the [children].
 ///
@@ -40,6 +204,13 @@ const Duration _kExpand = Duration(milliseconds: 200);
 /// ** See code in examples/api/lib/material/expansion_tile/expansion_tile.0.dart **
 /// {@end-tool}
 ///
+/// {@tool dartpad}
+/// This example demonstrates how an [ExpansionTileController] can be used to
+/// programatically expand or collapse an [ExpansionTile].
+///
+/// ** See code in examples/api/lib/material/expansion_tile/expansion_tile.1.dart **
+/// {@end-tool}
+///
 /// See also:
 ///
 ///  * [ListTile], useful for creating expansion tile [children] when the
@@ -74,6 +245,7 @@ class ExpansionTile extends StatefulWidget {
     this.collapsedShape,
     this.clipBehavior,
     this.controlAffinity,
+    this.controller,
   }) : assert(
        expandedCrossAxisAlignment != CrossAxisAlignment.baseline,
        'CrossAxisAlignment.baseline is not supported since the expanded children '
@@ -310,6 +482,13 @@ class ExpansionTile extends StatefulWidget {
   /// which means that the expansion arrow icon will appear on the tile's trailing edge.
   final ListTileControlAffinity? controlAffinity;
 
+  /// If provided, the controller can be used to expand and collapse tiles.
+  ///
+  /// In cases were control over the tile's state is needed from a callback triggered
+  /// by a widget within the tile, [ExpansionTileController.of] may be more convenient
+  /// than supplying a controller.
+  final ExpansionTileController? controller;
+
   @override
   State<ExpansionTile> createState() => _ExpansionTileState();
 }
@@ -324,7 +503,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   final ColorTween _iconColorTween = ColorTween();
   final ColorTween _backgroundColorTween = ColorTween();
 
-  late AnimationController _controller;
+  late AnimationController _animationController;
   late Animation<double> _iconTurns;
   late Animation<double> _heightFactor;
   late Animation<ShapeBorder?> _border;
@@ -333,37 +512,43 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   late Animation<Color?> _backgroundColor;
 
   bool _isExpanded = false;
+  late ExpansionTileController _tileController;
 
   @override
   void initState() {
     super.initState();
-    _controller = AnimationController(duration: _kExpand, vsync: this);
-    _heightFactor = _controller.drive(_easeInTween);
-    _iconTurns = _controller.drive(_halfTween.chain(_easeInTween));
-    _border = _controller.drive(_borderTween.chain(_easeOutTween));
-    _headerColor = _controller.drive(_headerColorTween.chain(_easeInTween));
-    _iconColor = _controller.drive(_iconColorTween.chain(_easeInTween));
-    _backgroundColor = _controller.drive(_backgroundColorTween.chain(_easeOutTween));
+    _animationController = AnimationController(duration: _kExpand, vsync: this);
+    _heightFactor = _animationController.drive(_easeInTween);
+    _iconTurns = _animationController.drive(_halfTween.chain(_easeInTween));
+    _border = _animationController.drive(_borderTween.chain(_easeOutTween));
+    _headerColor = _animationController.drive(_headerColorTween.chain(_easeInTween));
+    _iconColor = _animationController.drive(_iconColorTween.chain(_easeInTween));
+    _backgroundColor = _animationController.drive(_backgroundColorTween.chain(_easeOutTween));
 
     _isExpanded = PageStorage.maybeOf(context)?.readState(context) as bool? ?? widget.initiallyExpanded;
     if (_isExpanded) {
-      _controller.value = 1.0;
+      _animationController.value = 1.0;
     }
+
+    assert(widget.controller?._state == null);
+    _tileController = widget.controller ?? ExpansionTileController();
+    _tileController._state = this;
   }
 
   @override
   void dispose() {
-    _controller.dispose();
+    _tileController._state = null;
+    _animationController.dispose();
     super.dispose();
   }
 
-  void _handleTap() {
+  void _toggleExpansion() {
     setState(() {
       _isExpanded = !_isExpanded;
       if (_isExpanded) {
-        _controller.forward();
+        _animationController.forward();
       } else {
-        _controller.reverse().then<void>((void value) {
+        _animationController.reverse().then<void>((void value) {
           if (!mounted) {
             return;
           }
@@ -377,6 +562,10 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
     widget.onExpansionChanged?.call(_isExpanded);
   }
 
+  void _handleTap() {
+    _toggleExpansion();
+  }
+
   // Platform or null affinity defaults to trailing.
   ListTileControlAffinity _effectiveAffinity(ListTileControlAffinity? affinity) {
     switch (affinity ?? ListTileControlAffinity.trailing) {
@@ -491,7 +680,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   @override
   Widget build(BuildContext context) {
     final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);
-    final bool closed = !_isExpanded && _controller.isDismissed;
+    final bool closed = !_isExpanded && _animationController.isDismissed;
     final bool shouldRemoveChildren = closed && !widget.maintainState;
 
     final Widget result = Offstage(
@@ -509,7 +698,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
     );
 
     return AnimatedBuilder(
-      animation: _controller.view,
+      animation: _animationController.view,
       builder: _buildChildren,
       child: shouldRemoveChildren ? null : result,
     );

packages/flutter/test/material/expansion_tile_test.dart

@@ -729,4 +729,119 @@ void main() {
       expect(getTextColor(), theme.colorScheme.primary);
     });
   });
+
+  testWidgets('ExpansionTileController isExpanded, expand() and collapse()', (WidgetTester tester) async {
+    final ExpansionTileController controller = ExpansionTileController();
+
+    await tester.pumpWidget(MaterialApp(
+      home: Material(
+        child: ExpansionTile(
+          controller: controller,
+          title: const Text('Title'),
+          children: const <Widget>[
+            Text('Child 0'),
+          ],
+        ),
+      ),
+    ));
+
+    expect(find.text('Child 0'), findsNothing);
+    expect(controller.isExpanded, isFalse);
+    controller.expand();
+    expect(controller.isExpanded, isTrue);
+    await tester.pumpAndSettle();
+    expect(find.text('Child 0'), findsOneWidget);
+    expect(controller.isExpanded, isTrue);
+    controller.collapse();
+    expect(controller.isExpanded, isFalse);
+    await tester.pumpAndSettle();
+    expect(find.text('Child 0'), findsNothing);
+  });
+
+  testWidgets('Calling ExpansionTileController.expand/collapsed has no effect if it is already expanded/collapsed', (WidgetTester tester) async {
+    final ExpansionTileController controller = ExpansionTileController();
+
+    await tester.pumpWidget(MaterialApp(
+      home: Material(
+        child: ExpansionTile(
+          controller: controller,
+          title: const Text('Title'),
+          initiallyExpanded: true,
+          children: const <Widget>[
+            Text('Child 0'),
+          ],
+        ),
+      ),
+    ));
+
+    expect(find.text('Child 0'), findsOneWidget);
+    expect(controller.isExpanded, isTrue);
+    controller.expand();
+    expect(controller.isExpanded, isTrue);
+    await tester.pump();
+    expect(tester.hasRunningAnimations, isFalse);
+    expect(find.text('Child 0'), findsOneWidget);
+    controller.collapse();
+    expect(controller.isExpanded, isFalse);
+    await tester.pump();
+    expect(tester.hasRunningAnimations, isTrue);
+    await tester.pumpAndSettle();
+    expect(controller.isExpanded, isFalse);
+    expect(find.text('Child 0'), findsNothing);
+    controller.collapse();
+    expect(controller.isExpanded, isFalse);
+    await tester.pump();
+    expect(tester.hasRunningAnimations, isFalse);
+  });
+
+  testWidgets('Call to ExpansionTileController.of()', (WidgetTester tester) async {
+    final GlobalKey titleKey = GlobalKey();
+    final GlobalKey childKey = GlobalKey();
+    await tester.pumpWidget(MaterialApp(
+      home: Material(
+        child: ExpansionTile(
+          initiallyExpanded: true,
+          title: Text('Title', key: titleKey),
+          children: <Widget>[
+            Text('Child 0', key: childKey),
+          ],
+        ),
+      ),
+    ));
+
+    final ExpansionTileController controller1 = ExpansionTileController.of(childKey.currentContext!);
+    expect(controller1.isExpanded, isTrue);
+
+    final ExpansionTileController controller2 = ExpansionTileController.of(titleKey.currentContext!);
+    expect(controller2.isExpanded, isTrue);
+
+    expect(controller1, controller2);
+  });
+
+  testWidgets('Call to ExpansionTile.maybeOf()', (WidgetTester tester) async {
+    final GlobalKey titleKey = GlobalKey();
+    final GlobalKey nonDescendantKey = GlobalKey();
+    await tester.pumpWidget(MaterialApp(
+      home: Material(
+        child: Column(
+          children: <Widget>[
+            ExpansionTile(
+              title: Text('Title', key: titleKey),
+              children: const <Widget>[
+                Text('Child 0'),
+              ],
+            ),
+            Text('Non descendant', key: nonDescendantKey),
+          ],
+        ),
+      ),
+    ));
+
+    final ExpansionTileController? controller1 = ExpansionTileController.maybeOf(titleKey.currentContext!);
+    expect(controller1, isNotNull);
+    expect(controller1?.isExpanded, isFalse);
+
+    final ExpansionTileController? controller2 = ExpansionTileController.maybeOf(nonDescendantKey.currentContext!);
+    expect(controller2, isNull);
+  });
 }