Selector<A, S> constructor

Selector<A, S>(
  1. {Key key,
  2. @required ValueWidgetBuilder<S> builder,
  3. @required S selector(
    1. BuildContext,
    2. A
    ),
  4. ShouldRebuild<S> shouldRebuild,
  5. Widget child}
)

An equivalent to Consumer that can filter updates by selecting a limited amount of values and prevent rebuild if they don't change.

Selector will obtain a value using Provider.of, then pass that value to selector. That selector callback is then tasked to return an object that contains only the informations needed for builder to complete.

By default, Selector determines if builder needs to be called again by comparing the previous and new result of selector using DeepCollectionEquality from the package collecton.

This behavior can be overriden by passing a custom shouldRebuild callback.

NOTE: The selected value must be immutable, or otherwise Selector may think nothing changed and not call builder again.

As such, it selector should return either a collection (List/Map/Set/Iterable) or a class that override ==.

To select multiple values without having to write a class that implements ==, the easiest solution is to use a "Tuple" from tuple:

Selector<Foo, Tuple2<Bar, Baz>>(
  selector: (_, foo) => Tuple2(foo.bar, foo.baz),
  builder: (_, data, __) {
    return Text('${data.item1}  ${data.item2}');
  }
)

In that example, builder will be called again only if foo.bar or foo.baz changes.

For generic usage informations, see Consumer.

Implementation

Selector({
  Key key,
  @required ValueWidgetBuilder<S> builder,
  @required S Function(BuildContext, A) selector,
  ShouldRebuild<S> shouldRebuild,
  Widget child,
})  : assert(selector != null),
      super(
        key: key,
        shouldRebuild: shouldRebuild,
        builder: builder,
        selector: (context) => selector(context, Provider.of(context)),
        child: child,
      );