Add `getInheritedWidgetOfExactType` to `BuildContext` (#121276)

* Add getInheritedWidgetOfExactType to BuildContext

* Use the new API in all the places

* Fix doc error

* Review Changes

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

@@ -319,7 +319,7 @@ abstract class FocusTraversalPolicy with Diagnosticable {
   Iterable<FocusNode> sortDescendants(Iterable<FocusNode> descendants, FocusNode currentNode);
 
   _FocusTraversalGroupScope? _getMarker(BuildContext? context) {
-    return context?.getElementForInheritedWidgetOfExactType<_FocusTraversalGroupScope>()?.widget as _FocusTraversalGroupScope?;
+    return context?.getInheritedWidgetOfExactType<_FocusTraversalGroupScope>();
   }
 
   // Sort all descendants, taking into account the FocusTraversalGroup
@@ -941,7 +941,7 @@ class _ReadingOrderSortData with Diagnosticable {
   // Find the directionality in force for a build context without creating a
   // dependency.
   static TextDirection? _findDirectionality(BuildContext context) {
-    return (context.getElementForInheritedWidgetOfExactType<Directionality>()?.widget as Directionality?)?.textDirection;
+    return context.getInheritedWidgetOfExactType<Directionality>()?.textDirection;
   }
 
   /// Finds the common Directional ancestor of an entire list of groups.
@@ -1439,7 +1439,7 @@ class FocusTraversalOrder extends InheritedWidget {
   /// If no [FocusTraversalOrder] ancestor exists, or the order is null, this
   /// will assert in debug mode, and throw an exception in release mode.
   static FocusOrder of(BuildContext context) {
-    final FocusTraversalOrder? marker = context.getElementForInheritedWidgetOfExactType<FocusTraversalOrder>()?.widget as FocusTraversalOrder?;
+    final FocusTraversalOrder? marker = context.getInheritedWidgetOfExactType<FocusTraversalOrder>();
     assert(() {
       if (marker == null) {
         throw FlutterError(
@@ -1464,7 +1464,7 @@ class FocusTraversalOrder extends InheritedWidget {
   ///
   /// If no [FocusTraversalOrder] ancestor exists, or the order is null, returns null.
   static FocusOrder? maybeOf(BuildContext context) {
-    final FocusTraversalOrder? marker = context.getElementForInheritedWidgetOfExactType<FocusTraversalOrder>()?.widget as FocusTraversalOrder?;
+    final FocusTraversalOrder? marker = context.getInheritedWidgetOfExactType<FocusTraversalOrder>();
     return marker?.order;
   }
 

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

@@ -2216,10 +2216,13 @@ abstract class BuildContext {
   /// be called apply to this method as well.
   InheritedWidget dependOnInheritedElement(InheritedElement ancestor, { Object? aspect });
 
-  /// Obtains the nearest widget of the given type `T`, which must be the type of a
-  /// concrete [InheritedWidget] subclass, and registers this build context with
-  /// that widget such that when that widget changes (or a new widget of that
-  /// type is introduced, or the widget goes away), this build context is
+  /// Returns the nearest widget of the given type `T` and creates a dependency
+  /// on it, or null if no appropriate widget is found.
+  ///
+  /// The widget found will be a concrete [InheritedWidget] subclass, and
+  /// calling [dependOnInheritedWidgetOfExactType] registers this build context
+  /// with the returned widget. When that widget changes (or a new widget of
+  /// that type is introduced, or the widget goes away), this build context is
   /// rebuilt so that it can obtain new values from that widget.
   ///
   /// {@template flutter.widgets.BuildContext.dependOnInheritedWidgetOfExactType}
@@ -2230,8 +2233,8 @@ abstract class BuildContext {
   /// [State.initState] methods, because those methods would not get called
   /// again if the inherited value were to change. To ensure that the widget
   /// correctly updates itself when the inherited value changes, only call this
-  /// (directly or indirectly) from build methods, layout and paint callbacks, or
-  /// from [State.didChangeDependencies].
+  /// (directly or indirectly) from build methods, layout and paint callbacks,
+  /// or from [State.didChangeDependencies].
   ///
   /// This method should not be called from [State.dispose] because the element
   /// tree is no longer stable at that time. To refer to an ancestor from that
@@ -2240,8 +2243,8 @@ abstract class BuildContext {
   /// whenever the widget is removed from the tree.
   ///
   /// It is also possible to call this method from interaction event handlers
-  /// (e.g. gesture callbacks) or timers, to obtain a value once, if that value
-  /// is not going to be cached and reused later.
+  /// (e.g. gesture callbacks) or timers, to obtain a value once, as long as
+  /// that value is not cached and/or reused later.
   ///
   /// Calling this method is O(1) with a small constant factor, but will lead to
   /// the widget being rebuilt more often.
@@ -2252,13 +2255,34 @@ abstract class BuildContext {
   /// the widget or one of its ancestors is moved (for example, because an
   /// ancestor is added or removed).
   ///
-  /// The [aspect] parameter is only used when `T` is an
-  /// [InheritedWidget] subclasses that supports partial updates, like
-  /// [InheritedModel]. It specifies what "aspect" of the inherited
-  /// widget this context depends on.
+  /// The [aspect] parameter is only used when `T` is an [InheritedWidget]
+  /// subclass that supports partial updates, like [InheritedModel]. It
+  /// specifies what "aspect" of the inherited widget this context depends on,
+  /// where the meaning of the aspect is determined by the specific subclass.
   /// {@endtemplate}
   T? dependOnInheritedWidgetOfExactType<T extends InheritedWidget>({ Object? aspect });
 
+  /// Returns the nearest widget of the given [InheritedWidget] subclass `T` or
+  /// null if an appropriate ancestor is not found.
+  ///
+  /// This method does not introduce a dependency the way that the more typical
+  /// [dependOnInheritedWidgetOfExactType] does, so this context will not be
+  /// rebuilt if the [InheritedWidget] changes. This function is meant for those
+  /// uncommon use cases where a dependency is undesirable.
+  ///
+  /// This method should not be called from [State.dispose] because the element
+  /// tree is no longer stable at that time. To refer to an ancestor from that
+  /// method, save a reference to the ancestor in [State.didChangeDependencies].
+  /// It is safe to use this method from [State.deactivate], which is called
+  /// whenever the widget is removed from the tree.
+  ///
+  /// It is also possible to call this method from interaction event handlers
+  /// (e.g. gesture callbacks) or timers, to obtain a value once, as long as
+  /// that value is not cached and/or reused later.
+  ///
+  /// Calling this method is O(1) with a small constant factor.
+  T? getInheritedWidgetOfExactType<T extends InheritedWidget>();
+
   /// Obtains the element corresponding to the nearest widget of the given type `T`,
   /// which must be the type of a concrete [InheritedWidget] subclass.
   ///
@@ -4111,7 +4135,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
       // implementation to decide whether to rebuild based on whether we had
       // dependencies here.
     }
-    _inheritedWidgets = null;
+    _inheritedElements = null;
     _lifecycleState = _ElementLifecycle.inactive;
   }
 
@@ -4306,7 +4330,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     return null;
   }
 
-  PersistentHashMap<Type, InheritedElement>? _inheritedWidgets;
+  PersistentHashMap<Type, InheritedElement>? _inheritedElements;
   Set<InheritedElement>? _dependencies;
   bool _hadUnsatisfiedDependencies = false;
 
@@ -4347,7 +4371,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   @override
   T? dependOnInheritedWidgetOfExactType<T extends InheritedWidget>({Object? aspect}) {
     assert(_debugCheckStateIsActiveForAncestorLookup());
-    final InheritedElement? ancestor = _inheritedWidgets == null ? null : _inheritedWidgets![T];
+    final InheritedElement? ancestor = _inheritedElements == null ? null : _inheritedElements![T];
     if (ancestor != null) {
       return dependOnInheritedElement(ancestor, aspect: aspect) as T;
     }
@@ -4355,10 +4379,15 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     return null;
   }
 
+  @override
+  T? getInheritedWidgetOfExactType<T extends InheritedWidget>() {
+    return getElementForInheritedWidgetOfExactType<T>()?.widget as T?;
+  }
+
   @override
   InheritedElement? getElementForInheritedWidgetOfExactType<T extends InheritedWidget>() {
     assert(_debugCheckStateIsActiveForAncestorLookup());
-    final InheritedElement? ancestor = _inheritedWidgets == null ? null : _inheritedWidgets![T];
+    final InheritedElement? ancestor = _inheritedElements == null ? null : _inheritedElements![T];
     return ancestor;
   }
 
@@ -4378,7 +4407,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
 
   void _updateInheritance() {
     assert(_lifecycleState == _ElementLifecycle.active);
-    _inheritedWidgets = _parent?._inheritedWidgets;
+    _inheritedElements = _parent?._inheritedElements;
   }
 
   @override
@@ -5374,8 +5403,8 @@ class InheritedElement extends ProxyElement {
   void _updateInheritance() {
     assert(_lifecycleState == _ElementLifecycle.active);
     final PersistentHashMap<Type, InheritedElement> incomingWidgets =
-        _parent?._inheritedWidgets ?? const PersistentHashMap<Type, InheritedElement>.empty();
-    _inheritedWidgets = incomingWidgets.put(widget.runtimeType, this);
+        _parent?._inheritedElements ?? const PersistentHashMap<Type, InheritedElement>.empty();
+    _inheritedElements = incomingWidgets.put(widget.runtimeType, this);
   }
 
   @override

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

@@ -359,7 +359,7 @@ class Scrollable extends StatefulWidget {
   /// If there is no [Scrollable] in the widget tree above the [context], this
   /// method returns false.
   static bool recommendDeferredLoadingForContext(BuildContext context) {
-    final _ScrollableScope? widget = context.getElementForInheritedWidgetOfExactType<_ScrollableScope>()?.widget as _ScrollableScope?;
+    final _ScrollableScope? widget = context.getInheritedWidgetOfExactType<_ScrollableScope>();
     if (widget == null) {
       return false;
     }

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

@@ -121,7 +121,7 @@ class SharedAppData extends StatefulWidget {
   /// 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 _SharedAppModel? model = context.getElementForInheritedWidgetOfExactType<_SharedAppModel>()?.widget as _SharedAppModel?;
+    final _SharedAppModel? model = context.getInheritedWidgetOfExactType<_SharedAppModel>();
     assert(_debugHasSharedAppData(model, context, 'setValue'));
     model!.sharedAppDataState.setValue<K, V>(key, value);
   }

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

@@ -95,7 +95,7 @@ class TickerMode extends StatefulWidget {
   /// In the absence of a [TickerMode] widget, this function returns a
   /// [ValueNotifier], whose [ValueNotifier.value] is always true.
   static ValueNotifier<bool> getNotifier(BuildContext context) {
-    final _EffectiveTickerMode? widget = context.getElementForInheritedWidgetOfExactType<_EffectiveTickerMode>()?.widget as _EffectiveTickerMode?;
+    final _EffectiveTickerMode? widget = context.getInheritedWidgetOfExactType<_EffectiveTickerMode>();
     return widget?.notifier ?? ValueNotifier<bool>(true);
   }
 

packages/flutter/test/widgets/inherited_test.dart

@@ -423,6 +423,32 @@ void main() {
     expect(buildCount, equals(2));
   });
 
+  testWidgets("BuildContext.getInheritedWidgetOfExactType doesn't create a dependency", (WidgetTester tester) async {
+    int buildCount = 0;
+    final GlobalKey<void> inheritedKey = GlobalKey();
+    final ChangeNotifier notifier = ChangeNotifier();
+
+    final Widget builder = Builder(
+      builder: (BuildContext context) {
+        expect(context.getInheritedWidgetOfExactType<ChangeNotifierInherited>(), equals(inheritedKey.currentWidget));
+        buildCount += 1;
+        return Container();
+      },
+    );
+
+    final Widget inner = ChangeNotifierInherited(
+      key: inheritedKey,
+      notifier: notifier,
+      child: builder,
+    );
+
+    await tester.pumpWidget(inner);
+    expect(buildCount, equals(1));
+    notifier.notifyListeners();
+    await tester.pumpWidget(inner);
+    expect(buildCount, equals(1));
+  });
+
   testWidgets('initState() dependency on Inherited asserts', (WidgetTester tester) async {
     // This is a regression test for https://github.com/flutter/flutter/issues/5491
     bool exceptionCaught = false;

packages/flutter/test/widgets/router_test.dart

@@ -1360,7 +1360,7 @@ testWidgets('ChildBackButtonDispatcher take priority recursively', (WidgetTester
       routeInformationProvider: provider,
       routeInformationParser: CustomRouteInformationParser((RouteInformation information, BuildContext context) {
         parserCalled = true;
-        final DefaultTextStyle style = context.getElementForInheritedWidgetOfExactType<DefaultTextStyle>()!.widget as DefaultTextStyle;
+        final DefaultTextStyle style = context.getInheritedWidgetOfExactType<DefaultTextStyle>()!;
         return RouteInformation(location: '${style.maxLines}');
       }),
       routerDelegate: SimpleRouterDelegate(