provider 2.0.0+1
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An helper to easily exposes a value using InheritedWidget without having to write one.

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A dependency injection system built with widgets for widgets. provider is mostly syntax sugar for InheritedWidget, to make common use-cases straightforward.

Usage #

Exposing a value #

To expose a variable using provider, wrap any widget into one of the provider widgets from this package and pass it your variable. Then, all descendants of the newly added provider widget can access this variable.

A simple example would be to wrap the entire application into a Provider widget and pass it our variable:

Provider<String>.value(
  value: 'Hello World',
  child: MaterialApp(
    home: Home(),
  )
)

Alternatively, for complex objects, most providers expose a constructor that takes a function to create the value. The provider will call that function only once, when inserting the widget in the tree, and expose the result. This is perfect for exposing a complex object that never changes over time without writing a StatefulWidget.

The following creates and expose a MyComplexClass. And in the event where we remove Provider from the widget tree, the instantiated MyComplexClass will be disposed.

Provider<MyComplexClass>(
  builder: (context) => MyComplexClass(),
  dispose: (context, value) => value.dispose()
  child: SomeWidget(),
)

Reading a value #

The easiest way to read a value is by using the static method Provider.of<T>(BuildContext context). This method will look up in widget tree starting from the widget associated to the BuildContext passed and it will return the nearest variable of type T found (or throw if nothing if found).

Combined with the first example of exposing a value, this widget will read the exposed String and render "Hello World."

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text(
      /// Don't forget to pass the type of the object you want to obtain to `Provider.of`!
      Provider.of<String>(context)
    );
  }
}

Alternatively instead of using Provider.of, we can use the Consumer widget.

This can be useful for performances optimizations or when it is difficult to obtain a BuildContext descendant of the provider.

Provider<String>.value(
  value: 'Hello World',
  child: Consumer<String>(
    builder: (context, value) => Text(value);
  ),
)

Note that you can freely use multiple providers with different types 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);

MultiProvider #

When injecting many values in big applications, Provider can rapidly become pretty nested:

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

In that situation, we can use MultiProvider to improve the readability:

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

The behavior of both examples is strictly the same. MultiProvider only changes the appearance of the code.

Existing providers #

provider expose a few different kind of "provider" for different types of objects.

namedescription
ProviderThe most basic form of provider. It takes a value and expose it, whatever the value is.
ListenableProviderA provider specific for Listenable object. Listenable will listen the object and ask widgets which depends on it to rebuild whenever the listener is called.
ChangeNotifierProviderA specification of ListenableProvider for ChangeNotifier. It will automatically call ChangeNotifier.dispose when needed.
ValueListenableProviderListen to a ValueListenable and only expose ValueListenable.value.
StreamProviderListen to a Stream and expose the latest value emitted.
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Publisher

dash-overflow.net

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

Repository (GitHub)
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Documentation

API reference

License

MIT (LICENSE)

Dependencies

flutter

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