Observing LiveData from ViewModel

Question

I have a separate class in which I handle data fetching (specifically Firebase) and I usually return LiveData objects from it and update them asynchronously. Now I want to have

Answer 1

Use Kotlin coroutines with Architecture components.

You can use the liveData builder function to call a suspend function, serving the result as a LiveData object.

val user: LiveData = liveData {
    val data = database.loadUser() // loadUser is a suspend function.
    emit(data)
}

You can also emit multiple values from the block. Each emit() call suspends the execution of the block until the LiveData value is set on the main thread.

val user: LiveData = liveData {
    emit(Result.loading())
    try {
        emit(Result.success(fetchUser()))
    } catch(ioException: Exception) {
        emit(Result.error(ioException))
    }
}

In your gradle config, use androidx.lifecycle:lifecycle-livedata-ktx:2.2.0 or higher.

There is also an article about it.

Update: Also it's possible to change LiveData in the Dao interface. You need to add the suspend keyword to the function:

@Query("SELECT * FROM the_table")
suspend fun getAll(): List

and in the ViewModel you need to get it asynchronously like that:

viewModelScope.launch(Dispatchers.IO) {
    allData = dao.getAll()
    // It's also possible to sync other data here
}