InheritedWidget class Null safety

Base class for widgets that efficiently propagate information down the tree.

To obtain the nearest instance of a particular type of inherited widget from a build context, use BuildContext.dependOnInheritedWidgetOfExactType.

Inherited widgets, when referenced in this way, will cause the consumer to rebuild when the inherited widget itself changes state.

The following is a skeleton of an inherited widget called FrogColor:

class FrogColor extends InheritedWidget {
  const FrogColor({
    super.key,
    required this.color,
    required super.child,
  });

  final Color color;

  static FrogColor of(BuildContext context) {
    final FrogColor? result = context.dependOnInheritedWidgetOfExactType<FrogColor>();
    assert(result != null, 'No FrogColor found in context');
    return result!;
  }

  @override
  bool updateShouldNotify(FrogColor old) => color != old.color;
}

Implementing the `of` method

The convention is to provide a static method of on the InheritedWidget which does the call to BuildContext.dependOnInheritedWidgetOfExactType. This allows the class to define its own fallback logic in case there isn't a widget in scope. In the example above, the value returned will be null in that case, but it could also have defaulted to a value.

Sometimes, the of method returns the data rather than the inherited widget; for example, in this case it could have returned a Color instead of the FrogColor widget.

Occasionally, the inherited widget is an implementation detail of another class, and is therefore private. The of method in that case is typically put on the public class instead. For example, Theme is implemented as a StatelessWidget that builds a private inherited widget; Theme.of looks for that inherited widget using BuildContext.dependOnInheritedWidgetOfExactType and then returns the ThemeData.

Calling the `of` method

When using the of method, the context must be a descendant of the InheritedWidget, meaning it must be "below" the InheritedWidget in the tree.

In this example, the context used is the one from the Builder, which is a child of the FrogColor widget, so this works.

class MyPage extends StatelessWidget {
  const MyPage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: FrogColor(
        color: Colors.green,
        child: Builder(
          builder: (BuildContext innerContext) {
            return Text(
              'Hello Frog',
              style: TextStyle(color: FrogColor.of(innerContext).color),
            );
          },
        ),
      ),
    );
  }
}

In this example, the context used is the one from the MyOtherPage widget, which is a parent of the FrogColor widget, so this does not work.

class MyOtherPage extends StatelessWidget {
  const MyOtherPage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: FrogColor(
        color: Colors.green,
        child: Text(
          'Hello Frog',
          style: TextStyle(color: FrogColor.of(context).color),
        ),
      ),
    );
  }
}

Constructors

InheritedWidget({Key? key, required Widget child}): Abstract const constructor. This constructor enables subclasses to provide const constructors so that they can be used in const expressions.
const

Properties

child → Widget: The widget below this widget in the tree.
finalinherited
hashCode → int: The hash code for this object.
nonVirtual">@nonVirtualread-onlyinherited
key → Key?: Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType → Type: A representation of the runtime type of the object.
read-onlyinherited

Methods

createElement() → InheritedElement: Inflates this configuration to a concrete instance.
override
debugDescribeChildren() → List<DiagnosticsNode>: Returns a list of DiagnosticsNode objects describing this node's children.
protected">@protectedinherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void: Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a non-existent method or property is accessed.
inherited
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode: Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) → String: A string representation of this object.
inherited
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a string representation of this node and its descendants.
inherited
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a one-line detailed description of the object.
inherited
toStringShort() → String: A short, textual description of this widget.
inherited
updateShouldNotify(covariant InheritedWidget oldWidget) → bool: Whether the framework should notify widgets that inherit from this widget.
protected">@protected

Operators

operator ==(Object other) → bool: The equality operator.
nonVirtual">@nonVirtualinherited

Flutter
widgets
InheritedWidget abstract class