Provider<T> class

A Provider that manages the lifecycle of the value it provides by delegating to a pair of Create and Dispose.

It is usually used to avoid making a StatefulWidget for something trivial, such as instantiating a BLoC.

Provider is the equivalent of a State.initState combined with State.dispose. Create is called only once in State.initState. We cannot use InheritedWidget as it requires the value to be constructor-initialized and final.

The following example instantiates a Model once, and disposes it when Provider is removed from the tree.

class Model {
  void dispose() {}
}

class Stateless extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Provider<Model>(
      create: (context) =>  Model(),
      dispose: (context, value) => value.dispose(),
      child: ...,
    );
  }
}

It is worth noting that the create callback is lazily called. It is called the first time the value is read, instead of the first time Provider is inserted in the widget tree.

This behavior can be disabled by passing lazy: false to Provider.

Testing

When testing widgets that consumes providers, it is necessary to add the proper providers in the widget tree above the tested widget.

A typical test may look like this:

final foo = MockFoo();

await tester.pumpWidget(
  Provider<Foo>.value(
    value: foo,
    child: TestedWidget(),
  ),
);

Note this example purposefully specified the object type, instead of having it inferred. Since we used a mocked class (typically using mockito), then we have to downcast the mock to the type of the mocked class. Otherwise, the type inference will resolve to Provider<MockFoo> instead of Provider<Foo>, which will cause Provider.of<Foo> to fail.

Inheritance

Constructors

Provider({Key? key, required Create<T> create, Dispose<T>? dispose, bool? lazy, TransitionBuilder? builder, Widget? child}): Creates a value, store it, and expose it to its descendants.
Provider.value({Key? key, required T value, UpdateShouldNotify<T>? updateShouldNotify, TransitionBuilder? builder, Widget? child}): Expose an existing value without disposing it.

Properties

builder → TransitionBuilder?: Syntax sugar for obtaining a BuildContext that can read the provider created.
finalinherited
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

Methods

build(BuildContext context) → Widget: Describes the part of the user interface represented by this widget.
inherited
buildWithChild(BuildContext context, Widget? child) → Widget: A build method that receives an extra child parameter.
inherited
createElement() → _InheritedProviderElement<T>: Creates a StatelessElement to manage this widget's location in the tree.
inherited
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}) → 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

Static Properties

debugCheckInvalidValueType ↔ (void Function<T>(T value)?): A sanity check to prevent misuse of Provider when a variant should be used instead.
getter/setter pair

Static Methods

of<T>(BuildContext context, {bool listen = true}) → T: Obtains the nearest Provider<T> up its widget tree and returns its value.