access BlocProvider.of<Bloc>(context) in dispose method

Question

does anyone have any idea of how I can do this?

My code:

  @override
  void dispose() {
    final FiltersBloc filtersBloc = 
       BlocProvider.of<FiltersBloc>(context);
    super.dispose();
  }

error is:

flutter:         BlocProvider.of() called with a context that does not contain a Bloc of type FiltersBloc.
flutter:         No ancestor could be found starting from the context that was passed to
flutter: BlocProvider.of<FiltersBloc>().
flutter:
flutter:         This can happen if:
flutter:         1. The context you used comes from a widget above the BlocProvider.
flutter:         2. You used MultiBlocProvider and didn't explicity provide the BlocProvider types.
flutter:
flutter:         Good: BlocProvider<FiltersBloc>(builder: (context) => FiltersBloc())
flutter:         Bad: BlocProvider(builder: (context) => FiltersBloc()).
flutter:
flutter:         The context used was: FiltersDrawer(dirty, state: _FiltersDrawerState#86e8a)

Also, if I follow the error code and use final filtersBloc = BlocProvider<FiltersBloc>(builder: (context) => FiltersBloc()) instead, I cannot call filtersBloc.dispatch() anymore.

I know for initState, we can just didChangeDependencies instead. But I cannot find an equivalent for dispose.

Any help would be greatly appreciated. Thanks!

Modillion

hello wei. why would you need to get the Bloc inside dispose? do you want to dispose the Bloc object here? – Willywillynilly

No, I want to dispatch an event to my bloc when dispose of the widget – Modillion

how about declare the final FiltersBloc filtersBloc = BlocProvider.of<FiltersBloc>(context); in a parent widget then pass it as a parameter so that on dispose, you can use widget.filtersBloc.dispatch(); – Willywillynilly

Thanks, i got my answer from here: github.com/felangel/bloc/issues/588. It's basically what you said. Thanks – Modillion

Answer 1

BlockProvider needs context to be initialized. You may initialize it on the screen's Widget build()

late FiltersBloc filtersBloc;

@override
Widget build(BuildContext context){
  filtersBloc = BlocProvider.of<FiltersBloc>(context);
  return ...
}

...then call the desired method on dispose()

@override
void dispose() {
  filtersBloc.dispatch();
  super.dispose();
}

Supplicate

You should point out that late is only for projects which are null safety. – Categorize

this answer is not correct, didChangeDependencies should be used instead of build method – Carycaryatid

@Carycaryatid : why do you suggest didChangeDependencies? you mean because of this explanation – Assumed

Answer 2

A small more detailed approach:

sound null safety, you can use @Omatt answer.

unsound null safety, you can use the following approach:

Declare a static variable inside the class and assign it inside init or build as follows:

class MyAwesomeWidget extends StatefulWidget {
  const MyAwesomeWidget({
    Key key,
  });

  @override
  _MyAwesomeWidgetState createState() => _MyAwesomeWidgetState();
}

class _MyAwesomeWidgetState extends State<MyAwesomeWidget> {
  FiltersBloc filtersBloc;

  @override
  void initState() {
    super.initState();
    new Future.delayed(Duration.zero, () {
      filterBloc = BlocProvider.of<FiltersBloc>(context);
    });
  }

  @override
  void dispose() {
    filterBloc.myFunction();
    super.dispose();
  }
}

Categorize