Added widgets/AppModel (#92297)

examples/api/lib/widgets/app_model/app_model.0.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 AppModel
+
+import 'package:flutter/material.dart';
+
+class ShowAppModelValue extends StatelessWidget {
+  const ShowAppModelValue({ Key? key, required this.appModelKey }) : super(key: key);
+
+  final String appModelKey;
+
+  @override
+  Widget build(BuildContext context) {
+    // The AppModel.getValue() call here causes this widget to depend
+    // on the value of the AppModel's 'foo' key. If it's changed, with
+    // AppModel.setValue(), then this widget will be rebuilt.
+    final String value = AppModel.getValue<String, String>(context, appModelKey, () => 'initial');
+    return Text('$appModelKey: $value');
+  }
+}
+
+// Demonstrates that changes to the AppModel _only_ cause the dependent widgets
+// to be rebuilt. In this case that's the ShowAppModelValue widget that's
+// displaying the value of a key whose value has been updated.
+class Home extends StatefulWidget {
+  const Home({ Key? key }) : super(key: key);
+
+  @override
+  State<Home> createState() => _HomeState();
+}
+
+class _HomeState extends State<Home> {
+  int _fooVersion = 0;
+  int _barVersion = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: Center(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: <Widget>[
+            const ShowAppModelValue(appModelKey: 'foo'),
+            const SizedBox(height: 16),
+            const ShowAppModelValue(appModelKey: 'bar'),
+            const SizedBox(height: 16),
+            ElevatedButton(
+              child: const Text('change foo'),
+              onPressed: () {
+                _fooVersion += 1;
+                // Changing the AppModel's value for 'foo' causes the widgets that
+                // depend on 'foo' to be rebuilt.
+                AppModel.setValue<String, String?>(context, 'foo', 'FOO $_fooVersion'); // note: no setState()
+              },
+            ),
+            const SizedBox(height: 16),
+            ElevatedButton(
+              child: const Text('change bar'),
+              onPressed: () {
+                _barVersion += 1;
+                AppModel.setValue<String, String?>(context, 'bar', 'BAR $_barVersion');  // note: no setState()
+              },
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+void main() {
+  runApp(const MaterialApp(home: Home()));
+}

examples/api/lib/widgets/app_model/app_model.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 AppModel
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+
+// A single lazily constructed object that's shared with the entire
+// application via `SharedObject.of(context)`. The value of the object
+// can be changed with `SharedObject.reset(context)`. Resetting the value
+// will cause all of the widgets that depend on it to be rebuilt.
+class SharedObject {
+  SharedObject._();
+
+  static final Object _sharedObjectKey = Object();
+
+  @override
+  String toString() => describeIdentity(this);
+
+  static void reset(BuildContext context) {
+    // Calling AppModel.set() causes dependent widgets to be rebuilt.
+    AppModel.setValue<Object, SharedObject>(context, _sharedObjectKey, SharedObject._());
+  }
+
+  static SharedObject of(BuildContext context) {
+    // If a value for _sharedObjectKey has never been set then the third
+    // callback parameter is used to generate an initial value.
+    return AppModel.getValue<Object, SharedObject>(context, _sharedObjectKey, () => SharedObject._());
+  }
+}
+
+// An example of a widget which depends on the SharedObject's value,
+// which might be provided - along with SharedObject - in a Dart package.
+class CustomWidget extends StatelessWidget {
+  const CustomWidget({ Key? key }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    // Will be rebuilt if the shared object's value is changed.
+    return ElevatedButton(
+      child: Text('Replace ${SharedObject.of(context)}'),
+      onPressed: () {
+        SharedObject.reset(context);
+      },
+    );
+  }
+}
+
+class Home extends StatelessWidget {
+  const Home({ Key? key }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const Scaffold(
+      body: Center(
+        child: CustomWidget()
+      ),
+    );
+  }
+}
+
+void main() {
+  runApp(const MaterialApp(home: Home()));
+}

packages/flutter/lib/src/widgets/app.dart

@@ -9,6 +9,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 
 import 'actions.dart';
+import 'app_model.dart';
 import 'banner.dart';
 import 'basic.dart';
 import 'binding.dart';
@@ -1664,6 +1665,7 @@ class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
 
     return RootRestorationScope(
       restorationId: widget.restorationScopeId,
+      child: AppModel(
         child: Shortcuts(
           debugLabel: '<Default WidgetsApp Shortcuts>',
           shortcuts: widget.shortcuts ?? WidgetsApp.defaultShortcuts,
@@ -1679,6 +1681,7 @@ class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
             ),
           ),
         ),
+      ),
     );
   }
 }

packages/flutter/lib/src/widgets/app_model.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/foundation.dart';
+
+import 'framework.dart';
+import 'inherited_model.dart';
+
+/// The type of the [AppModel.getValue] `init` parameter.
+///
+/// This callback is used to lazily create the initial value for
+/// an [AppModel] keyword.
+typedef AppModelInitCallback<T> = T Function();
+
+/// Enables sharing key/value data with its `child` and all of the
+/// child's descendants.
+///
+/// - `AppModel.getValue(context, key, initCallback)` creates a dependency
+/// on the key and returns the value for the key from the shared data table.
+/// If no value exists for key then the initCallback is used to create
+/// the initial value.
+///
+/// - `AppModel.setValue(context, key, value)` changes the value of an entry
+/// in the shared data table and forces widgets that depend on that entry
+/// to be rebuilt.
+///
+/// A widget whose build method uses AppModel.getValue(context,
+/// keyword, initCallback) creates a dependency on the AppModel. When
+/// the value of keyword changes with AppModel.setValue(), the widget
+/// will be rebuilt. The values managed by the AppModel are expected
+/// to be immutable: intrinsic changes to values will not cause
+/// dependent widgets to be rebuilt.
+///
+/// An instance of this widget is created automatically by [WidgetsApp].
+///
+/// There are many ways to share data with a widget subtree. This
+/// class is based on [InheritedModel], which is an [InheritedWidget].
+/// It's intended to be used by packages that need to share a modest
+/// number of values among their own components.
+///
+/// AppModel is not intended to be a substitute for Provider or any of
+/// the other general purpose application state systems. AppModel is
+/// for situations where a package's custom widgets need to share one
+/// or a handful of immutable data objects that can be lazily
+/// initialized. It exists so that packages like that can deliver
+/// custom widgets without requiring the developer to add a
+/// package-specific umbrella widget to their application.
+///
+/// A good way to create an AppModel key that avoids potential
+/// collisions with other packages is to use a static `Object()` value.
+/// The `SharedObject` example below does this.
+///
+/// {@tool dartpad}
+/// The following sample demonstrates using the automatically created
+/// `AppModel`. Button presses cause changes to the values for keys
+/// 'foo', and 'bar', and those changes only cause the widgets that
+/// depend on those keys to be rebuilt.
+///
+/// ** See code in examples/api/lib/widgets/app_model/app_model.0.dart **
+/// {@end-tool}
+///
+/// {@tool dartpad}
+/// The following sample demonstrates how a single lazily computed
+/// value could be shared within an app. A Flutter package that
+/// provided custom widgets might use this approach to share a (possibly
+/// private) value with instances of those widgets.
+///
+/// ** See code in examples/api/lib/widgets/app_model/app_model.1.dart **
+/// {@end-tool}
+class AppModel extends StatefulWidget {
+  /// Creates a widget based on [InheritedModel] that supports build
+  /// dependencies qualified by keywords. Descendant widgets create
+  /// such dependencies with [AppModel.getValue] and they trigger
+  /// rebuilds with [AppModel.setValue].
+  ///
+  /// This widget is automatically created by the [WidgetsApp].
+  const AppModel({ Key? key, required this.child }) : super(key: key);
+
+  /// The widget below this widget in the tree.
+  ///
+  /// {@macro flutter.widgets.ProxyWidget.child}
+  final Widget child;
+
+  @override
+  State<StatefulWidget> createState() => _AppModelState();
+
+  /// Returns the app model's value for `key` and ensures that each
+  /// time the value of `key` is changed with [AppModel.setValue], the
+  /// specified context will be rebuilt.
+  ///
+  /// If no value for `key` exists then the `init` callback is used to
+  /// generate an initial value. The callback is expected to return
+  /// an immutable value because intrinsic changes to the value will
+  /// not cause dependent widgets to be rebuilt.
+  ///
+  /// A widget that depends on the app model's value for `key` should use
+  /// this method in their `build` methods to ensure that they are rebuilt
+  /// if the value changes.
+  ///
+  /// The type parameter `K` is the type of the keyword and `V`
+  /// is the type of the value.
+  static V getValue<K extends Object, V>(BuildContext context, K key, AppModelInitCallback<V> init) {
+    final _AppModelData? model = InheritedModel.inheritFrom<_AppModelData>(context, aspect: key);
+    assert(_debugHasAppModel(model, context, 'getValue'));
+    return model!.appModelState.getValue<K, V>(key, init);
+  }
+
+  /// Changes the app model's `value` for `key` and rebuilds any widgets
+  /// that have created a dependency on `key` with [AppModel.getValue].
+  ///
+  /// If `value` is `==` to the current value of `key` then nothing
+  /// is rebuilt.
+  ///
+  /// The `value` is expected to be immutable because intrinsic
+  /// changes to the value will not cause dependent widgets to be
+  /// rebuilt.
+  ///
+  /// Unlike [AppModel.getValue], this method does _not_ create a dependency
+  /// between `context` and `key`.
+  ///
+  /// The type parameter `K` is the type of the value's keyword and `V`
+  /// is the type of the value.
+  static void setValue<K extends Object, V>(BuildContext context, K key, V value) {
+    final _AppModelData? model = context.getElementForInheritedWidgetOfExactType<_AppModelData>()?.widget as _AppModelData?;
+    assert(_debugHasAppModel(model, context, 'setValue'));
+    model!.appModelState.setValue<K, V>(key, value);
+  }
+
+  static bool _debugHasAppModel(_AppModelData? model, BuildContext context, String methodName) {
+    assert(() {
+      if (model == null) {
+        throw FlutterError.fromParts(
+          <DiagnosticsNode>[
+            ErrorSummary('No AppModel widget found.'),
+            ErrorDescription('AppModel.$methodName requires an AppModel widget ancestor.\n'),
+            context.describeWidget('The specific widget that could not find an AppModel ancestor was'),
+            context.describeOwnershipChain('The ownership chain for the affected widget is'),
+            ErrorHint(
+              'Typically, the AppModel widget is introduced by the MaterialApp '
+              'or WidgetsApp widget at the top of your application widget tree. It '
+              'provides a key/value map of data that is shared with the entire '
+              'application.',
+            ),
+          ],
+        );
+      }
+      return true;
+    }());
+    return true;
+  }
+}
+
+class _AppModelState extends State<AppModel> {
+  late Map<Object, Object?> data = <Object, Object?>{};
+
+  @override
+  Widget build(BuildContext context) {
+    return _AppModelData(appModelState: this, child: widget.child);
+  }
+
+  V getValue<K extends Object, V>(K key, AppModelInitCallback<V> init) {
+    data[key] ??= init();
+    return data[key] as V;
+  }
+
+  void setValue<K extends Object, V>(K key, V value) {
+    if (data[key] != value) {
+      setState(() {
+        data = Map<Object, Object?>.from(data);
+        data[key] = value;
+      });
+    }
+  }
+}
+
+class _AppModelData extends InheritedModel<Object> {
+  _AppModelData({
+    Key? key,
+    required this.appModelState,
+    required Widget child
+  }) : data = appModelState.data, super(key: key, child: child);
+
+  final _AppModelState appModelState;
+  final Map<Object, Object?> data;
+
+  @override
+  bool updateShouldNotify(_AppModelData old) {
+    return data != old.data;
+  }
+
+  @override
+  bool updateShouldNotifyDependent(_AppModelData old, Set<Object> keys) {
+    for (final Object key in keys) {
+      if (data[key] != old.data[key]) {
+        return true;
+      }
+    }
+    return false;
+  }
+}

packages/flutter/lib/widgets.dart

@@ -22,6 +22,7 @@ export 'src/widgets/animated_size.dart';
 export 'src/widgets/animated_switcher.dart';
 export 'src/widgets/annotated_region.dart';
 export 'src/widgets/app.dart';
+export 'src/widgets/app_model.dart';
 export 'src/widgets/async.dart';
 export 'src/widgets/autocomplete.dart';
 export 'src/widgets/autofill.dart';

packages/flutter/test/material/debug_test.dart

@@ -200,6 +200,8 @@ void main() {
       '     _FocusMarker\n'
       '     Focus\n'
       '     Shortcuts\n'
+      '     _AppModelData\n'
+      '     AppModel\n'
       '     UnmanagedRestorationScope\n'
       '     RestorationScope\n'
       '     UnmanagedRestorationScope\n'

packages/flutter/test/widgets/app_model_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/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('AppModel basics', (WidgetTester tester) async {
+    int columnBuildCount = 0;
+    int child1BuildCount = 0;
+    int child2BuildCount = 0;
+    late void Function(BuildContext context) setAppModelValue;
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: AppModel(
+          child: Builder(
+            builder: (BuildContext context) {
+              columnBuildCount += 1;
+              return GestureDetector(
+                behavior: HitTestBehavior.opaque,
+                onTap: () {
+                  setAppModelValue.call(context);
+                },
+                child: Column(
+                  children: <Widget>[
+                    Builder(
+                      builder: (BuildContext context) {
+                        child1BuildCount += 1;
+                        return Text(AppModel.getValue<String, String>(context, 'child1Text', () => 'null'));
+                      },
+                    ),
+                    Builder(
+                      builder: (BuildContext context) {
+                        child2BuildCount += 1;
+                        return Text(AppModel.getValue<String, String>(context, 'child2Text', () => 'null'));
+                      }
+                    ),
+                  ],
+                ),
+              );
+            },
+          ),
+        ),
+      ),
+    );
+
+    expect(columnBuildCount, 1);
+    expect(child1BuildCount, 1);
+    expect(child2BuildCount, 1);
+    expect(find.text('null').evaluate().length, 2);
+
+    // AppModel.setValue<String, String>(context, 'child1Text', 'child1')
+    // causes the first Text widget to be rebuilt with its text to be
+    // set to 'child1'. Nothing else is rebuilt.
+    setAppModelValue = (BuildContext context) {
+      AppModel.setValue<String, String>(context, 'child1Text', 'child1');
+    };
+    await tester.tap(find.byType(GestureDetector));
+    await tester.pump();
+    expect(columnBuildCount, 1);
+    expect(child1BuildCount, 2);
+    expect(child2BuildCount, 1);
+    expect(find.text('child1'), findsOneWidget);
+    expect(find.text('null'), findsOneWidget);
+
+    // AppModel.setValue<String, String>(context, 'child2Text', 'child1')
+    // causes the second Text widget to be rebuilt with its text to be
+    // set to 'child2'. Nothing else is rebuilt.
+    setAppModelValue = (BuildContext context) {
+      AppModel.setValue<String, String>(context, 'child2Text', 'child2');
+    };
+    await tester.tap(find.byType(GestureDetector));
+    await tester.pump();
+    expect(columnBuildCount, 1);
+    expect(child1BuildCount, 2);
+    expect(child2BuildCount, 2);
+    expect(find.text('child1'), findsOneWidget);
+    expect(find.text('child2'), findsOneWidget);
+
+    // Resetting a key's value to the same value does not
+    // cause any widgets to be rebuilt.
+    setAppModelValue = (BuildContext context) {
+      AppModel.setValue<String, String>(context, 'child1Text', 'child1');
+      AppModel.setValue<String, String>(context, 'child2Text', 'child2');
+    };
+    await tester.tap(find.byType(GestureDetector));
+    await tester.pump();
+    expect(columnBuildCount, 1);
+    expect(child1BuildCount, 2);
+    expect(child2BuildCount, 2);
+
+    // More of the same, resetting the values to null..
+
+    setAppModelValue = (BuildContext context) {
+      AppModel.setValue<String, String>(context, 'child1Text', 'null');
+    };
+    await tester.tap(find.byType(GestureDetector));
+    await tester.pump();
+    expect(columnBuildCount, 1);
+    expect(child1BuildCount, 3);
+    expect(child2BuildCount, 2);
+    expect(find.text('null'), findsOneWidget);
+    expect(find.text('child2'), findsOneWidget);
+
+    setAppModelValue = (BuildContext context) {
+      AppModel.setValue<String, String>(context, 'child2Text', 'null');
+    };
+    await tester.tap(find.byType(GestureDetector));
+    await tester.pump();
+    expect(columnBuildCount, 1);
+    expect(child1BuildCount, 3);
+    expect(child2BuildCount, 3);
+    expect(find.text('null').evaluate().length, 2);
+  });
+
+  testWidgets('WidgetsApp AppModel ', (WidgetTester tester) async {
+    int parentBuildCount = 0;
+    int childBuildCount = 0;
+
+    await tester.pumpWidget(
+      WidgetsApp(
+        color: const Color(0xff00ff00),
+        builder: (BuildContext context, Widget? child) {
+          parentBuildCount += 1;
+          return GestureDetector(
+            behavior: HitTestBehavior.opaque,
+            onTap: () {
+              AppModel.setValue<String, String>(context, 'childText', 'child');
+            },
+            child: Center(
+              child: Builder(
+                builder: (BuildContext context) {
+                  childBuildCount += 1;
+                  return Text(AppModel.getValue<String, String>(context, 'childText', () => 'null'));
+                },
+              ),
+            ),
+          );
+        },
+      ),
+    );
+
+    expect(find.text('null'), findsOneWidget);
+    expect(parentBuildCount, 1);
+    expect(childBuildCount, 1);
+
+    await tester.tap(find.byType(GestureDetector));
+    await tester.pump();
+    expect(parentBuildCount, 1);
+    expect(childBuildCount, 2);
+    expect(find.text('child'), findsOneWidget);
+  });
+
+  testWidgets('WidgetsApp AppModel Shadowing', (WidgetTester tester) async {
+    int innerTapCount = 0;
+    int outerTapCount = 0;
+
+    await tester.pumpWidget(
+      WidgetsApp(
+        color: const Color(0xff00ff00),
+        builder: (BuildContext context, Widget? child) {
+          return GestureDetector(
+            behavior: HitTestBehavior.opaque,
+            onTap: () {
+              outerTapCount += 1;
+              AppModel.setValue<String, String>(context, 'childText', 'child');
+            },
+            child: Center(
+              child: AppModel(
+                child: Builder(
+                  builder: (BuildContext context) {
+                    return GestureDetector(
+                      onTap: () {
+                        innerTapCount += 1;
+                        AppModel.setValue<String, String>(context, 'childText', 'child');
+                      },
+                      child: Text(AppModel.getValue<String, String>(context, 'childText', () => 'null')),
+                    );
+                  },
+                ),
+              ),
+            ),
+          );
+        },
+      ),
+    );
+
+    expect(find.text('null'), findsOneWidget);
+
+    await tester.tapAt(const Offset(10, 10));
+    await tester.pump();
+    expect(outerTapCount, 1);
+    expect(innerTapCount, 0);
+    expect(find.text('null'), findsOneWidget);
+
+    await tester.tap(find.text('null'));
+    await tester.pump();
+    expect(outerTapCount, 1);
+    expect(innerTapCount, 1);
+    expect(find.text('child'), findsOneWidget);
+  });
+}