StateSelector<S, U> class

A widget that builds itself based on a part of the state from a StateReadable.

StateSelector allows you to optimize rebuilds by only rebuilding when a specific part of the state changes, selected by the selector function.

{@tool snippet} This example shows how to use StateSelector to only rebuild when a specific property of the state changes:

class UserForm extends StatelessWidget {
  final UserController userController;

  const UserForm({
    required this.userController,
    super.key,
  });

  @override
  Widget build(BuildContext context) => StateSelector<UserState, bool>(
    stateReadable: userController,
    selector: (state) => state.isLoading,
    builder: (context, isLoading, _) => isLoading
        ? const CircularProgressIndicator()
        : const Text('User loaded'),
  );
}

// A state readable implementation for user
class UserController implements StateReadable<UserState> {
  // Implementation details...

  @override
  UserState get state => const UserState(); // Example implementation

  @override
  Stream<UserState> get stream => Stream.empty(); // Example implementation
}

// Assume we have a complex state with multiple properties
class UserState {
  final String name;
  final bool isLoading;
  final List<String> permissions;

  const UserState({
    this.name = '',
    this.isLoading = false,
    this.permissions = const <String>[],
  });
}

{@end-tool}

See also:

  • StateBuilder, which rebuilds the UI when the entire state changes.
  • StateListener, which performs side effects in response to state changes.
  • StateConsumer, which combines both rebuilding and side effects.
Inheritance

Constructors

StateSelector({required StateReadable<S> stateReadable, required StateWidgetSelector<S, U> selector, required StateWidgetBuilder<U> builder, Widget? child, Key? key})
Creates a new StateSelector.
const

Properties

builder → StateWidgetBuilder<U>
The builder that builds a widget based on the selected value.
final
child → Widget?
The child of the widget.
final
hashCode → int
The hash code for this object.
no setterinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
selector → StateWidgetSelector<S, U>
The function that extracts a value from the state.
final
stateReadable → StateReadable<S>
The source of the state.
final

Methods

createElement() → StatefulElement
Creates a StatefulElement to manage this widget's location in the tree.
inherited
createState() → State<StateSelector<S, U>>
Creates the mutable state for this widget at a given location in the tree.
override
debugDescribeChildren() → List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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, int wrapWidth = 65}) → 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

Operators

operator ==(Object other) → bool
The equality operator.
inherited