更新[24/04/19]:我刚刚发现该库已经为我们提供了一种方法来使用PagedList.BoundaryCallback<YourItem>
来听取空的初始负载。
*请注意,我的旧答案仍然是一个有效的选择。
val livedPageList = LivePagedListBuilder(sourceFactory, config)
.setBoundaryCallback(object: PagedList.BoundaryCallback<YourItem>() {
override fun onZeroItemsLoaded() {
super.onZeroItemsLoaded()
// Handle empty initial load here
}
override fun onItemAtEndLoaded(itemAtEnd: YourItem) {
super.onItemAtEndLoaded(itemAtEnd)
// Here you can listen to last item on list
}
override fun onItemAtFrontLoaded(itemAtFront: YourItem) {
super.onItemAtFrontLoaded(itemAtFront)
// Here you can listen to first item on list
}
})
.build()
原答案:
基于这个类在谷歌样本Network State。修改它以处理initialLoad中的空内容。
@Suppress("DataClassPrivateConstructor")
data class NetworkState private constructor(
val status: Status,
val msg: String? = null
) {
enum class Status {
RUNNING,
SUCCESS_LOADED, // New
SUCCESS_EMPTY, // New
FAILED
}
companion object {
val EMPTY = NetworkState(Status.SUCCESS_EMPTY) // New
val LOADED = NetworkState(Status.SUCCESS_LOADED) // New
val LOADING = NetworkState(Status.RUNNING)
fun error(msg: String?) = NetworkState(Status.FAILED, msg)
}
}
用法如下:
class DataSource: PageKeyedDataSource<Long, Item>() {
val initialLoad: MutableLiveData<NetworkState> = MutableLiveData()
override fun loadInitial(params: LoadInitialParams<Long>, callback: LoadInitialCallback<Long, Item>) {
initialLoad.postValue(NetworkState.LOADING)
apiCallSource.subscribe({ items ->
if (items.isEmpty()) {
initialLoad.postValue(NetworkState.EMPTY)
} else {
initialLoad.postValue(NetworkState.LOADED)
}
}, { error ->
// handle error
})
}
}
这就是活动处理它的方式:
class activity: AppCompatActivity() {
val viewModel = // init viewmodel
override fun onCreate(savedInstanceState: Bundle?) {
viewModel.refreshState.observe(this, Observer { networkState ->
if (it == NetworkState.LOADING) {
// Show loading
} else {
// Hide loading
if (it.status == NetworkState.Status.SUCCESS_EMPTY) {
// Show empty state for initial load
}
}
}
}
}
有关如何将DataSource与Activity连接的更多详细信息,请参阅此sample
只需在DataSourceFactory
和DataSource
中添加一个监听器或回调函数,如果loadInitial
中的列表为空,则调用它:
class DataSourceFactory(
private val dataObservable: Observable<List<Data>>,
private val onEmptyAction: () -> Unit
) : DataSource.Factory<Int, Data >() {
override fun create(): DataSource {
return DataSource(observable, onEmptyAction)
}
}
class DataSource(
private val observable: Observable<List<Data>>,
private val onEmptyAction: () -> Unit
) : ItemKeyedDataSource<Int, Data>() {
private val data = mutableListOf<Data>()
override fun loadInitial(params: LoadInitialParams<Int>, callback: LoadInitialCallback<Data>) {
observable
.subscribe({ data ->
if (data.isEmpty()) {
// Inform someone that this list is empty from the
// beginning to be able to show an empty page
onEmptyAction()
}
// rest of your code & logic
}, { Timber.e(it) })
}
}