psteiger

sealed class Resource<out T> {
    
    data class Success<out T>(val data: T) : Resource<T>()
    data class Loading<out T>(val partialData: T? = null) : Resource<T>()
    data class Failure<out T>(val throwable: Throwable? = null) : Resource<T>()

    val extractData: T? get() = when (this) {
        is Success -> data
        is Loading -> partialData
        is Failure -> null

psteiger

inline fun <reified T> DataSnapshot.getTypedValue(): T {
    val genericTypeIndicator = object : GenericTypeIndicator<T>() {}
    return getValue(genericTypeIndicator)!!
}

psteiger

class UsersViewModel : ViewModel() {
    
    private val usersSnapLiveData: LiveData<Resource<DataSnapshot>> by lazy { 
        UsersSnapLiveData() 
    }
 
    val usersLiveData: LiveData<Resource<HashMap<String, User>>> by lazy {
        usersSnapLiveData.mapLiveDataResource<
                DataSnapshot,                  // from
                HashMap<String, User>          // to

psteiger

inline fun <reified T> LiveData<Resource<DataSnapshot>>.mapGetValue(): LiveData<Resource<T>> = map {
    it.getTypedValueResource<T>()
}

inline fun <reified T> Resource<DataSnapshot>.getTypedValueResource(): Resource<T> = mapResource {
    it.getTypedValue<T>()
}

psteiger

class UsersViewModel : ViewModel() {
    
    private val usersSnapLiveData: LiveData<Resource<DataSnapshot>> by lazy { 
        UsersSnapLiveData() 
    }
 
    val usersLiveData: LiveData<Resource<HashMap<String, User>>> by lazy {
        usersSnapLiveData.mapGetValue<HashMap<String, User>>()
    }
    

psteiger

class UserFragment : Fragment() {

    private var usersViewModel: UserViewModel? = null

    override fun onCreateView(
        inflater: LayoutInflater, 
        container: ViewGroup?, 
        savedInstanceState: Bundle?
    ): View? = inflater.inflate(R.layout.fragment_users, container, false)

psteiger

fun <T> Resource<T>.onSuccess(
    onSuccess: (data: T) -> Unit
): Resource<T> {
    if (this is Resource.Success<T>)
        onSuccess(data)

    return this
}

fun <T> Resource<T>.onLoading(

psteiger

inline fun <T> Resource<List<T>>.filterResource(predicate: (T) -> Boolean): Resource<List<T>> = try {
    when (this) {
        is Resource.Success<List<T>> -> Resource.Success<List<T>>(data.filter(predicate))
        is Resource.Loading<List<T>> -> Resource.Loading<List<T>>(partialData?.filter(predicate))
        is Resource.Failure<List<T>> -> Resource.Failure<List<T>>(throwable)
    }
} catch (e: Throwable) {
    Resource.Failure<List<T>>(e)
}

psteiger

sealed class Resource<out T> {
    
    data class Success<out T>(val data: T) : Resource<T>()
    data class Loading<out T>(val partialData: T? = null) : Resource<T>()
    data class Failure<out T>(val throwable: Throwable? = null) : Resource<T>()

    val extractData: T? get() = when (this) {
        is Success -> data
        is Loading -> partialData
        is Failure -> null

psteiger

open class FirebaseResourceLiveData(ref: DatabaseReference) : LiveData<Resource<DataSnapshot>> {
    init { 
        value = Resource.Loading() // setValue() of LiveData
    }
    
    private val listener = MyValueEventListener()

    override fun onActive() { // we have observers!
        value = Resource.Loading(value?.extractData)
        query.addValueEventListener(listener)