_ModalScopeStatus as InheritedModel (#149022)

According to previous discussion at flutter/flutter#145389 (comment), this change makes `_ModalScopeStatus` an `InheritedModel` rather than an `InheritedWidget`, and provides the following methods.

- `isCurrentOf`
- `canPopOf`
- `settingsOf`

For example, `ModalRoute.of(context)!.settings` could become `ModalRoute.settingsOf(context)` as a performance optimization.

Author: LinXunFeng

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

@@ -179,7 +179,7 @@ class BackButtonIcon extends StatelessWidget {
 /// will override [color] for states where [ButtonStyle.foregroundColor] resolves to non-null.
 ///
 /// When deciding to display a [BackButton], consider using
-/// `ModalRoute.of(context)?.canPop` to check whether the current route can be
+/// `ModalRoute.canPopOf(context)` to check whether the current route can be
 /// popped. If that value is false (e.g., because the current route is the
 /// initial route), the [BackButton] will not have any effect when pressed,
 /// which could frustrate the user.

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

@@ -18,6 +18,7 @@ import 'focus_manager.dart';
 import 'focus_scope.dart';
 import 'focus_traversal.dart';
 import 'framework.dart';
+import 'inherited_model.dart';
 import 'modal_barrier.dart';
 import 'navigator.dart';
 import 'overlay.dart';
@@ -883,7 +884,16 @@ class _DismissModalAction extends DismissAction {
   }
 }
 
-class _ModalScopeStatus extends InheritedWidget {
+enum _ModalRouteAspect {
+  /// Specifies the aspect corresponding to [ModalRoute.isCurrent].
+  isCurrent,
+  /// Specifies the aspect corresponding to [ModalRoute.canPop].
+  canPop,
+  /// Specifies the aspect corresponding to [ModalRoute.settings].
+  settings,
+}
+
+class _ModalScopeStatus extends InheritedModel<_ModalRouteAspect> {
   const _ModalScopeStatus({
     required this.isCurrent,
     required this.canPop,
@@ -912,6 +922,15 @@ class _ModalScopeStatus extends InheritedWidget {
     description.add(FlagProperty('canPop', value: canPop, ifTrue: 'can pop'));
     description.add(FlagProperty('impliesAppBarDismissal', value: impliesAppBarDismissal, ifTrue: 'implies app bar dismissal'));
   }
+
+  @override
+  bool updateShouldNotifyDependent(covariant _ModalScopeStatus oldWidget, Set<_ModalRouteAspect> dependencies) {
+    return dependencies.any((_ModalRouteAspect dependency) => switch (dependency) {
+      _ModalRouteAspect.isCurrent => isCurrent != oldWidget.isCurrent,
+      _ModalRouteAspect.canPop    => canPop != oldWidget.canPop,
+      _ModalRouteAspect.settings  => route.settings != oldWidget.route.settings,
+    });
+  }
 }
 
 class _ModalScope<T> extends StatefulWidget {
@@ -1146,10 +1165,40 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// while it is visible (specifically, if [isCurrent] or [canPop] change value).
   @optionalTypeArgs
   static ModalRoute<T>? of<T extends Object?>(BuildContext context) {
-    final _ModalScopeStatus? widget = context.dependOnInheritedWidgetOfExactType<_ModalScopeStatus>();
-    return widget?.route as ModalRoute<T>?;
+    return _of<T>(context);
+  }
+
+  static ModalRoute<T>? _of<T extends Object?>(BuildContext context, [_ModalRouteAspect? aspect]) {
+    return InheritedModel.inheritFrom<_ModalScopeStatus>(context, aspect: aspect)?.route as ModalRoute<T>?;
   }
 
+  /// Returns [ModalRoute.isCurrent] for the modal route most closely associated
+  /// with the given context.
+  ///
+  /// Returns null if the given context is not associated with a modal route.
+  ///
+  /// Use of this method will cause the given [context] to rebuild any time that
+  /// the [ModalRoute.isCurrent] property of the ancestor [_ModalScopeStatus] changes.
+  static bool? isCurrentOf(BuildContext context) => _of(context, _ModalRouteAspect.isCurrent)?.isCurrent;
+
+  /// Returns [ModalRoute.canPop] for the modal route most closely associated
+  /// with the given context.
+  ///
+  /// Returns null if the given context is not associated with a modal route.
+  ///
+  /// Use of this method will cause the given [context] to rebuild any time that
+  /// the [ModalRoute.canPop] property of the ancestor [_ModalScopeStatus] changes.
+  static bool? canPopOf(BuildContext context) => _of(context, _ModalRouteAspect.canPop)?.canPop;
+
+  /// Returns [ModalRoute.settings] for the modal route most closely associated
+  /// with the given context.
+  ///
+  /// Returns null if the given context is not associated with a modal route.
+  ///
+  /// Use of this method will cause the given [context] to rebuild any time that
+  /// the [ModalRoute.settings] property of the ancestor [_ModalScopeStatus] changes.
+  static RouteSettings? settingsOf(BuildContext context) => _of(context, _ModalRouteAspect.settings)?.settings;
+
   /// Schedule a call to [buildTransitions].
   ///
   /// Whenever you need to change internal state for a [ModalRoute] object, make

packages/flutter/test/material/bottom_sheet_test.dart

@@ -1357,7 +1357,7 @@ void main() {
       context: scaffoldKey.currentContext!,
       routeSettings: routeSettings,
       builder: (BuildContext context) {
-        retrievedRouteSettings = ModalRoute.of(context)!.settings;
+        retrievedRouteSettings = ModalRoute.settingsOf(context)!;
         return const Text('BottomSheet');
       },
     );

packages/flutter/test/widgets/navigator_test.dart

@@ -1431,7 +1431,7 @@ void main() {
                     settings: const RouteSettings(name: 'C'),
                     builder: (BuildContext context) {
                       log.add('building C');
-                      log.add('found ${ModalRoute.of(context)!.settings.name}');
+                      log.add('found ${ModalRoute.settingsOf(context)!.name}');
                       return TextButton(
                         child: const Text('C'),
                         onPressed: () {
@@ -1476,7 +1476,7 @@ void main() {
     final List<String> log = <String>[];
     Route<dynamic>? nextRoute = PageRouteBuilder<int>(
       pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
-        log.add('building page 1 - ${ModalRoute.of(context)!.canPop}');
+        log.add('building page 1 - ${ModalRoute.canPopOf(context)}');
         return const Placeholder();
       },
     );
@@ -1493,32 +1493,83 @@ void main() {
     expect(log, expected);
     key.currentState!.pushReplacement(PageRouteBuilder<int>(
       pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
-        log.add('building page 2 - ${ModalRoute.of(context)!.canPop}');
+        log.add('building page 2 - ${ModalRoute.canPopOf(context)}');
         return const Placeholder();
       },
     ));
     expect(log, expected);
     await tester.pump();
     expected.add('building page 2 - false');
-    expected.add('building page 1 - false'); // page 1 is rebuilt again because isCurrent changed.
     expect(log, expected);
     await tester.pump(const Duration(milliseconds: 150));
     expect(log, expected);
     key.currentState!.pushReplacement(PageRouteBuilder<int>(
       pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
-        log.add('building page 3 - ${ModalRoute.of(context)!.canPop}');
+        log.add('building page 3 - ${ModalRoute.canPopOf(context)}');
         return const Placeholder();
       },
     ));
     expect(log, expected);
     await tester.pump();
     expected.add('building page 3 - false');
-    expected.add('building page 2 - false'); // page 2 is rebuilt again because isCurrent changed.
     expect(log, expected);
     await tester.pump(const Duration(milliseconds: 200));
     expect(log, expected);
   });
 
+  testWidgets('ModelRoute can be partially depended-on', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> key = GlobalKey<NavigatorState>();
+    final List<String> log = <String>[];
+    Route<dynamic>? nextRoute = PageRouteBuilder<int>(
+      settings: const RouteSettings(name: 'page 1'),
+      pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
+        log.add('building ${ModalRoute.settingsOf(context)!.name} - canPop: ${ModalRoute.canPopOf(context)!}');
+        return const Placeholder();
+      },
+    );
+    await tester.pumpWidget(MaterialApp(
+      navigatorKey: key,
+      onGenerateRoute: (RouteSettings settings) {
+        assert(nextRoute != null);
+        final Route<dynamic> result = nextRoute!;
+        nextRoute = null;
+        return result;
+      },
+    ));
+    final List<String> expected = <String>['building page 1 - canPop: false'];
+    expect(log, expected);
+    key.currentState!.push(PageRouteBuilder<int>(
+      settings: const RouteSettings(name: 'page 2'),
+      pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
+        log.add('building ${ModalRoute.settingsOf(context)!.name} - isCurrent: ${ModalRoute.isCurrentOf(context)!}');
+        return const Placeholder();
+      },
+    ));
+    expect(log, expected);
+    await tester.pump();
+    expected.add('building page 2 - isCurrent: true');
+    expect(log, expected);
+    key.currentState!.push(PageRouteBuilder<int>(
+      settings: const RouteSettings(name: 'page 3'),
+      pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
+        log.add('building ${ModalRoute.settingsOf(context)!.name} - canPop: ${ModalRoute.canPopOf(context)!}');
+        return const Placeholder();
+      },
+    ));
+    expect(log, expected);
+    await tester.pump();
+    expected.add('building page 3 - canPop: true');
+    expected.add('building page 2 - isCurrent: false');
+    expect(log, expected);
+    key.currentState!.pop();
+    await tester.pump();
+    expected.add('building page 2 - isCurrent: true');
+    expect(log, expected);
+    key.currentState!.pop();
+    await tester.pump();
+    expect(log, expected);
+  });
+
   testWidgets('route semantics', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);
     final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{