Is it necessary to use return withContext(Dispatchers.IO)?-CodePudding

I'm using Firebase authentication. In the repository I have this function:

override suspend fun signIn(): Result<Boolean> {
    return try {
        auth.signInAnonymously().await()
        Result.Success(true)
    } catch (ex: Exception) {
        Result.Failure(ex)
    }
}

This function is called from within the ViewModel class:

var response by mutableStateOf<Result<Boolean>>(Result.Success(false))
    private set

fun signIn() = viewModelScope.launch {
    response = repository.signIn()
}

Which works fine but I was suggested to use in the ViewModel:

fun signIn() = viewModelScope.launch(Dispatchers.IO) {
    response = repository.signIn()
}

To add Dispatchers.IO and inside the repository:

override suspend fun signIn(): Result<Boolean> {
    return withContext(Dispatchers.IO) {
        try {
            auth.signInAnonymously().await()
            Result.Success(true)
        } catch (ex: Exception) {
            Result.Failure(ex)
        }
    }
}

To launch a coroutine using withContext. I and I don't understand why? I'm using Jetpack Compose.

CodePudding user response：

When you use the viewModelScope by default it starts a coroutine with main dispatcher but, you want to do a service call by using firebase services, then you should change your context to use IO dispatcher to don't block ui. So you use withContext(Dispatchers.IO) block.

CodePudding user response：

Actually, since you are already calling signIn from a coroutine started with Dispatchers.IO you don't have to use return withContext(...).

Since your repository method is suspend, it is able to call coroutines without special blocks like withContext.

// This line tells to launch code on separate IO thread, to avoid UI freezing
// Since default viewModelScope.launch runs on Dispatchers.Main, which is
// also used for rendering
fun signIn() = viewModelScope.launch(Dispatchers.IO) { 
    response = repository.signIn()
}