How to call a function from in ViewModel in viewModelScope?-CodePudding

In the repository class have this listener:

override fun getState(viewModelScope: CoroutineScope) = callbackFlow  {
    val listener = FirebaseAuth.AuthStateListener { auth ->
        trySend(auth.currentUser == null)
    }
    auth.addAuthStateListener(listener)
    awaitClose {
        auth.removeAuthStateListener(listener)
    }
}.stateIn(viewModelScope, SharingStarted.WhileSubscribed(), auth.currentUser == null)

In my ViewModel class I call getState function that returns a StateFlow<Boolean> using:

fun getState() = repo.getState(viewModelScope)

And I collect the data:

setContent {
    val state = viewModel.getState().collectAsState().value
}

If I change in ViewModel:

fun getState() = viewModelScope.launch {
    repo.getState(this)
}

So it can be called from a viewModelScope, I cannot collect the data anymore, as .collectAsState() appears in red. How to solve this? Any help would be greatly appreciated.

CodePudding user response：

I'm not sure why you're trying to do this:

fun getState() = viewModelScope.launch {
    repo.getState(this)
}

This code launches an unnecessary coroutine (doesn't call any suspending or blocking code) that get's a StateFlow reference and promptly releases the reference, and the function itself returns a Job (the launched coroutine). When you launch a coroutine, the coroutine doesn't produce any returned value. It just returns a Job instance that you can use to wait for it to finish or to cancel it early.

Your repository function already creates a StateFlow that runs in the passed scope, and you're already passing it viewModelScope, so your StateFlow was already running in the viewModelScope in your original code fun getState() = repo.getState(viewModelScope).

CodePudding user response：

Use live data to send your result of state flow from view model to activity. In your view model do like this:

 var isActive = MutableLiveData<Boolean>();

    fun getState() {
    viewModelScope.launch {
        repo.getState(this).onStart {

        }
            .collect(){
                isActive.value = it;
            }
    }

}

In your activity observer your liveData like this:

 viewModel.isActive.observe(this, Observer {
                Toast.makeText(applicationContext,it.toString(),Toast.LENGTH_LONG).show()
            })

Hopefully it will help.