flutter_bloc share state for many blocs

Question

let's say I want to check for internet connection every time I call Api, if there's no internet the call with throw exception like NoInternetException and then show a state screen to the user tells him to check their connection.

How can I achieve that without creating a new state for every bloc in flutter_bloc library?

Loïc Fonkam Loïc Fonkam · Accepted Answer · 2020-05-08T22:57:55

You can do this in the bloc that manages your root pages like authentication_page and homepage.

Create a state for noConnectivity.

NoConnectivity extends AuthenticationState{
  final String message;

  const NoConnectivity({ this.message });

}

Now create an event for noConnectivity.

NoConnectivityEvent extends AuthenticationEvent{}

Finally, create a StreamSubscription in your AuthenticationBloc to continuously listen to connecitvityState change and if the state is connectivity.none we'll trigger the NoConnecitivity state.

class AuthenticationBloc
    extends Bloc<AuthenticationEvent, AuthenticationState> {

StreamSubscription subscription;

 @override
  AuthenticationState get initialState => initialState();

  @override
  Stream<AuthenticationState> mapEventToState(
    AuthenticationEvent event,
  ) async* {
    // ... all other state map
   else if(event is NoConnectivityEvent) {
     yield* _mapNoConnectivityEventToState();
   }


Stream<AuthenticationState> _mapNoConnectivityEventToState() async * {
     subscription?.cancel();

     //Edit to handle android internet connectivity.
      subscription = Connectivity()
                    .onConnectivityChanged
                    .listen((ConnectivityResult result) {
                         if(Platform.isAndroid) {
                              try {
                                     final lookupResult = InternetAddress.lookup('google.com');
                                     if (lookupResult.isNotEmpty && lookupResult[0].rawAddress.isNotEmpty) {
                                         print('connected');
                                    }
                                  } on SocketException catch (error) {
                                       return add(NoConnectivityState(message: error.message ));
                                  }
                          } else if(result == ConnectivityResult.none ) {
                            return add(NoConnectivityState(message: "Noconnection")) ;

                          }
                           print("Connected");

                    });
}

  @override
  Future<void> close() {
    subscription?.cancel();
    return super.close();
  }

}

This subscription Stream will forever listen to a no connection and push the appropriate page you like to the state.

Required packages

rxdart

connectivity

Hope it helps!

flutter_bloc share state for many blocs

2 Answers