provider 1.5.0

An helper to easily exposes a value using InheritedWidget without having to write one.

A generic implementation of InheritedWidget. It allows to expose any kind of object, without having to manually write an InheritedWidget ourselves.

Usage

To expose a value, simply wrap any given part of your widget tree into any of the available Provider as such:

Provider<int>(
  value: 42,
  child: // ...
)

Descendants of Provider and now obtain this value using the static Provider.of<T> method:

var value = Provider.of<int>(context);

You can also use Consumer widget to insert a descendant, useful when both creating a Provider and using it:

Provider<int>(
  value: 42,
  child: Consumer<int>(
    builder: (context, value) => Text(value.toString()),
  )
)

---

Note that you can freely use multiple providers with different type together:

Provider<int>(
  value: 42,
  child: Provider<String>(
    value: 'Hello World',
    child: // ...
  )
)

And obtain their value independently:

var value = Provider.of<int>(context);
var value2 = Provider.of<String>(context);

Existing Providers:

Provider

A simple provider which takes the exposed value directly:

Provider<int>(
  value: 42,
  child: // ...
)

StatefulProvider

A provider that can also create and dispose an object.

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

StatefulBuilder is the equivalent of a State.initState combined with State.dispose. As such, valueBuilder is called only once and is unable to use InheritedWidget; which makes it impossible to update the created value.

If this is too limiting, consider instead HookProvider, which offer a much more advanced control over the created value.

The following example instanciate a Model once, and dispose it when StatefulProvider is removed from the tree.

class Model {
  void dispose() {}
}

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

HookProvider

A provider which can use hooks from flutter_hooks

This is especially useful to create complex providers, without having to make a StatefulWidget.

The following example uses BLoC pattern to create a BLoC, provide its value, and dispose it when the provider is removed from the tree.

HookProvider<MyBloc>(
  hook: () {
    final bloc = useMemoized(() => MyBloc());
    useEffect(() => bloc.dispose, [bloc]);
    return bloc;
  },
  child: // ...
)

MultiProvider

A provider that exposes that merges multiple other providers into one.

MultiProvider is used to improve the readability and reduce the boilerplate of having many nested providers.

As such, we're going from:

Provider<Foo>(
  value: foo,
  child: Provider<Bar>(
    value: bar,
    child: Provider<Baz>(
      value: baz,
      child: someWidget,
    )
  )
)

To:

MultiProvider(
  providers: [
    Provider<Foo>(value: foo),
    Provider<Bar>(value: bar),
    Provider<Baz>(value: baz),
  ],
  child: someWidget,
)

Technically, these two are identical. MultiProvider will convert the array into a tree. This changes only the appearance of the code.

StreamProvider

A provider that exposes the current value of a Stream as an AsyncSnapshot.

Changing [stream] will stop listening to the previous [stream] and listen the new one.

Removing [StreamProvider] from the tree will also stop listening to [stream]. To obtain the current value of type T, one must explicitly request Provider.of<AsyncSnapshot<T>>. It is also possible to use StreamProvider.of<T>.

Stream<int> foo;

StreamProvider<int>(
  stream: foo,
  child: Container(),
);