Question 75236 in Flutter Question posted in
The official Flutter documentation can be found here.

How to set a listener inside initState() in Flutter

So I want to write a BlocListener inside initState(), which functions to provide logic on whether a code should be executed or not based on the current state, like this:

@override
void initState() {
  super.initState();

  BlocListener<InternetCubit, InternetState>(
    listener: (context, stateInt) {
      if (stateInt is InternetConnectedState) {
        print('connected');
      } else if (stateInt is InternetNotConnectedState) {
        print('not connected');
      }
    },
  );
}

I’ve called this function right at the start of the application launch, and this code can work wherever and whenever an event occurs (in this case whether there is an internet connection or not) like this:
context.read<InternetCubit>().isInternetConnected();

But the code does not run or is not called.
I’ve tried doing research, but I’ve only found 1 piece of information]1 that says:

BlocListener only receives updates after it is mounted in the widget

Does using BlocListener only apply to Widgets, and not work in initState()?
Am I wrong in understanding the concept?

Thank you, please help..

Tags:

3

Answers


  1. 0

    Yes. You cannot call the bloc in that way. BlocListener is mainly used in the build method that is after mounting in the widget.

    One way would be. Use BlocListener inside the build method of the widget.

    BlocListener<SubjectBloc, SubjectState>(
            listener: (context, state) {
              // TODO: implement listener
            },
            child:  //add your child here.

    Now I assume you want to do implement that in the initstate.

    We can use the concept of streamsubscription.
    In the stateful widget. Declare a Stream Subscription

     late StreamSubscription _cubitStateSubscription;

    In the initstate() call the cubit and add listener to its stream

     InternetCubit internetCubit = context.read<InternetCubit>();
   _cubitStateSubscription = internetCubit.stream.listen((state) {
  //Access your state and implement logic
 
  });

    In the dispose method do not forget to cancel the stream:

       _cubitStateSubscription.cancel();

    Note: Both are the ways you can access your cubit. And there may be many but this would suffice.

    Login or Signup to reply.
  2. 0

    You can use the stream property of Cubit like this:

    @override
void initState() {
  super.initState();

  final InternetCubit internetCubit = BlocProvider.of<InternetCubit>(context);

  internetCubit.stream.listen((InternetState state) {
    if (stateInt is InternetConnectedState) {
      print('connected');
    } else if (stateInt is InternetNotConnectedState) {
      print('not connected');
    }
  });
}
    Login or Signup to reply.
  3. 0

    You can use BlocConsumer which provides listener . If it is about building ui based on state or state data BlocBuilders state is fine.

    BlocConsumer<SubjectBloc, SubjectState>(
    listener: (context, state) {
      // TODO: implement listener
    },
    builder: (context, state) {
      return Container();
    },
  )
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search