Android - A way to show/hide loader without writting false/true in every viewmodelScope.launch

Question

I have been writting a lot of code that looks like this

class LoginViewModel : ViewModel() {
    
    // A fragment observes this and shows/hides a progressbar
    val loader = MutableLiveData<Boolean>() 
    
    fun fetchSomeData() = viewModelScope.launch {
        loader.postValue(true)
        // ...
        loader.postValue(false)
    }
}

is there a way to do it in a more clean way? if I have to do 100 requests then there will be 200 lines of loader.postValue

Answer 1

If I interpret it correctly, you can basically wrap everything in a single method, and pass it a lambda:

fun launchWithPost(code: suspend () -> Unit) {
    viewModelScope.launch {
        loader.postValue(true)
        code.invoke()
        loader.postValue(false)
    }
}

fun fetchSomeData() = launchWithPost {
  // ...
}

Answer 2

Here is what I came up with:

fun Job.withLoader(state: MutableStateFlow<Boolean>) {
    state.tryEmit(true)
    invokeOnCompletion { state.tryEmit(false) }
}

fun Job.withLoader(state: MutableLiveData<Boolean>) {
    state.postValue(true)
    invokeOnCompletion { state.postValue(false) }
}

The usage:

fun authenticate(name: String, password: String) = viewModelScope.launch() {
    authRepo.authenticate(
        username = name,
        password = password,
    )
}.withLoader(loading)

Answer 3

I would leave handling the MutableLiveData<Boolean> and launching a coroutine separate. That way it's not bound to ViewModel at all. The best extension to add it to is the MutableLiveData value itself. Also you are not doing any kind of error handling. Is it correct not to set the value back to false on error?

fun fetchSomeData() = viewModelScope.launch {
    loader.run {
        //do your magic
    }
}


suspend fun MutableLiveData<Boolean>.run(code: suspend () -> Unit) {
    postValue(true)
    try {
        code.invoke()
    } finally {
        postValue(false)
    }
}