如何使用分页库Android在分页中使用空视图? [英] How to use empty view with pagination using paging library android?

问题描述

• 在设置适配器之前如何确定返回的数据大小?
• 如何将Emptyview与分页库一起使用?
• 如果pagedlist返回null或没有数据，如何设置emptyview?

推荐答案

更新[24/04/19]: 我刚刚发现该库已经为我们提供了一种使用PagedList.BoundaryCallback<YourItem>监听空初始负载的方法.

Update[24/04/19]: I just found out that the library already provide us a way to listen to empty initial load, using PagedList.BoundaryCallback<YourItem>.

*请注意，我的旧答案仍然是有效的选择.

*Note that my old answer is still a valid alternative.

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()

原始答案:

基于此类在Google示例上的

Based on this class on google sample Network State. Modify it to handle empty content in initialLoad.

@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
        })
    }
}

这是活动处理的方式:

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，请参见此

For more details on how to connect DataSource with Activity, see this sample

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