Helps to manage state for data loading.
Note: there is an alternative library of the same author called Replica.
For ordinary loading (without pagination) a state looks like that:
sealed class State<out T> {
object Empty : State<Nothing>()
object Loading : State<Nothing>()
data class Error(val throwable: Throwable) : State<Nothing>()
data class Data<T>(val data: T, val refreshing: Boolean) : State<T>()
}OrdinaryLoading manages loading state. To create it specify a suspend function that loads data. Use it in View Model:
interface ProfileRepository {
suspend fun loadProfile(): Profile
}class ProfileViewModel(private val profileRepository: ProfileRepository) : ViewModel() {
private val profileLoading = OrdinaryLoading(
viewModelScope,
load = { profileGateway.loadProfile() }
)
val profileState = profileLoading.stateFlow
init {
profileLoading.refresh()
}
fun onPullToRefresh() {
profileLoading.refresh()
}
}A state for FlowLoading is the same as for OrdinaryLoading. But FlowLoading allows to add a cache (an observable data source):
interface ProfileRepository {
suspend fun loadProfile(): Profile
fun observeProfile(): Flow<Profile?>
}
class ProfileViewModel(private val profileRepository: ProfileRepository) : ViewModel() {
private val profileLoading = FlowLoading(
viewModelScope,
load = { profileGateway.loadProfile() },
observe = { profileGateway.observeProfile() },
)
val profileState = profileLoading.stateFlow
init {
profileLoading.refresh()
}
fun onPullToRefresh() {
profileLoading.refresh()
}
}A paged loading state is more complex:
sealed class State<out T> {
object Empty : State<Nothing>()
object Loading : State<Nothing>()
data class Error(val throwable: Throwable) : State<Nothing>()
data class Data<T>(val data: List<T>, val status: DataStatus) : State<T>()
}
enum class DataStatus {
Normal,
Refreshing,
LoadingMore,
FullData
}To create PagedLoading specify how to load pages. Use it in View Model:
interface MoviesRepository {
suspend fun loadMovies(offset: Int, limit: Int): List<Movie>
}
class MoviesViewModel(private val moviesRepository: MoviesRepository) : ViewModel() {
companion object {
private const val PAGE_SIZE = 30
}
private val moviesLoading = PagedLoading<Movie>(
viewModelScope,
loadPage = {
val movies = moviesRepository.loadMovies(it.loadedData.size, PAGE_SIZE)
Page(movies, hasNextPage = movies.size >= PAGE_SIZE)
}
)
val moviesState = moviesLoading.stateFlow
init {
moviesLoading.refresh()
}
fun onPullToRefresh() {
moviesLoading.refresh()
}
fun onLoadMore() {
moviesLoading.loadMore()
}
}Loading shows an error as State.Error if there is no previously loaded data. If refreshing fails when some data has already been loaded an error dialog should be shown on top. To do it use handleErrors method:
init {
profileLoading.handleErrors(viewModelScope) { error ->
if (error.hasData) {
showErrorDialog(error.throwable)
}
}
}