每当我使用 flutter_bloc 关闭我的应用程序时如何重置为初始状态/值

Question

I am still a beginner when it comes to using flutter_bloc .

I have tried flutter_bloc and curious how to reset my bloc class to its initial value when I have closed the page.

my_bloc_class.dart

class sumtotal_detail_transactionsbloc extends Bloc<String, String>{
    @override
    String get initialState => '0';

    @override
    Stream<String> mapEventToState(String sumtotal_detail_transactions) async* {
        yield sumtotal_detail_transactions.toString();
    }
}

My widget with a BlocBuilder .

BlocBuilder<sumtotal_detail_transactionsbloc, String>(
    builder: (context,sumtotal_detail_transactions) => Text(
        sumtotal_detail_transactions,style: TextStyle(
                fontSize: 12,
                color: Colors.brown[300]
            ),
        )
),

Whenever I close the page or navigate to the page, how can I always/automatically reset the sumtotal_detail_transactions back to its initial value?

It will break my app if the value is always kept/store as it is.

Answer 1

Hey 👋 I would recommend providing the bloc in the page so when the page is closed the bloc is disposed automatically by BlocProvider. No need to have a reset event, just make sure to scope blocs only to the part of the widget tree that needs it. Hope that helps!

Answer 2

As mentioned by the plugin author here ,

I don't think it's a good idea to introduce a reset() because it directly goes against the bloc library paradigm: the only way to trigger a state change is by dispatching an event.

With that being said, you must add an event/state the will be used to trigger an initialisation event.

For example:

Add an initialisation event.

some_page_bloc_events.dart

class InitializePageEvent extends SomePageEvent {
  // You could also pass on some values here, if they come from the UI/page of your app
  @override
  String toString() => 'InitializePageEvent';
}

Add an initialisation state.

some_page_bloc_states.dart

class InitializePageState extends SomePageState {
  @override
  String toString() => 'InitializePageState';
}

Next, utilise these inside your bloc class to filter incoming events and notify the UI with the appropriate states.

some_page_bloc.dart

@override SomePageState get initialState => InitializePageState();

@override
Stream<SomePageState> mapEventToState(SomePageEvent event) async* {
    try {
        if(event is InitializePageEvent) {
            // Do whatever you like here
            yield InitializePageState();
        }
    } catch (e) {
        ...
    }
}

Finally, you can invoke the initialisation event wherever you deemed in necessary. In your case, it should be on the initState() method of your screen.

some_page.dart

@override
void initState() {
  super.initState();
  _someTransactionBloc.dispatch(InitializePageEvent());
}

Felix provided a well-written documentation for his plugin, I suggest that you go over the intro concepts how BLoC works. Please read it here .