How to handle error states with LiveData?

Question

The new LiveData can be used as a replacement for RxJava\'s observables in some scenarios. However, unlike Observable, LiveData has no callback for

Answer 1

Another approach is to use MediatorLiveData that will take sources of LiveData of different type. This will give you separation of each event:

For example:

open class BaseViewModel : ViewModel() {
    private val errorLiveData: MutableLiveData = MutableLiveData()
    private val loadingStateLiveData: MutableLiveData = MutableLiveData()
    lateinit var errorObserver: Observer
    lateinit var loadingObserver: Observer
    fun  fromPublisher(publisher: Publisher): MediatorLiveData {
        val mainLiveData = MediatorLiveData()
        mainLiveData.addSource(errorLiveData, errorObserver)
        mainLiveData.addSource(loadingStateLiveData, loadingObserver)
        publisher.subscribe(object : Subscriber {

            override fun onSubscribe(s: Subscription) {
                s.request(java.lang.Long.MAX_VALUE)
                loadingStateLiveData.postValue(LoadingState.LOADING)
            }

            override fun onNext(t: T) {
                mainLiveData.postValue(t)
            }

            override fun onError(t: Throwable) {
                errorLiveData.postValue(t)
            }

            override fun onComplete() {
                loadingStateLiveData.postValue(LoadingState.NOT_LOADING)
            }
        })

        return mainLiveData 
    }

}

In this example loading and error LiveData will start being observed once the MediatorLiveData will have active observers.