分页库的进度条和错误消息

Question

Paging Library 太棒了。但我发现缺少此功能：

加载数据时调度视图。假设我正在扩展 PageKeyedDataSource：调用 loadInitial 时顶部的视图，调用 loadAfter 时列表底部的视图。当 callback 被调用时，视图应该消失。
出现错误时调度视图。
滑动刷新

因为现在这是不可能的，有谁知道使用 PagingLibrary 的方法吗？至少一种在同一个列表中使用不同视图的方法。

Answer 1

有一个很好的示例@yigit 与 Paging 库相关，它还展示了如何在 Recyclerview 中处理进度条、错误和重试。所以基本上他正在创建一个 Listing.kt 数据 class，它由 NetworkState 和 PagedList 组成，如下所示

Listing.kt

data class Listing<T>(
        // the LiveData of paged lists for the UI to observe
        val pagedList: LiveData<PagedList<T>>,
        // represents the network request status to show to the user
        val networkState: LiveData<NetworkState>,
        // represents the refresh status to show to the user. Separate from networkState, this
        // value is importantly only when refresh is requested.
        val refreshState: LiveData<NetworkState>,
        // refreshes the whole data and fetches it from scratch.
        val refresh: () -> Unit,
        // retries any failed requests.
        val retry: () -> Unit)

NetworkState.kt

enum class Status {
    RUNNING,
    SUCCESS,
    FAILED
}

@Suppress("DataClassPrivateConstructor")
data class NetworkState private constructor(
        val status: Status,
        val msg: String? = null) {
    companion object {
        val LOADED = NetworkState(Status.SUCCESS)
        val LOADING = NetworkState(Status.RUNNING)
        fun error(msg: String?) = NetworkState(Status.FAILED, msg)
    }
}

RedditPostRepository.kt

interface RedditPostRepository {
    fun postsOfSubreddit(subReddit: String, pageSize: Int): Listing<RedditPost>

    enum class Type {
        IN_MEMORY_BY_ITEM,
        IN_MEMORY_BY_PAGE,
        DB
    }
}

SubRedditViewModel.k 观察来自 RedditPostRepository.kt 的 Listing<RedditPost> 通知 UI 有关状态和数据，UI 相应地更新视图。要了解有关 NetworkState 如何从 数据源传播到 ViewModel 的更多信息，请查看 PageKeyedSubredditDataSource.kt and SubRedditDataSourceFactory.kt

这是@yigit 对 Google 示例的 Link。

Answer 2

主要思想是保留对数据源工厂创建的数据源的引用。下面是来自 https://github.com/googlesamples/android-architecture-components/tree/master/PagingWithNetworkSample

的代码片段

class SubRedditDataSourceFactory(
    private val redditApi: RedditApi,
    private val subredditName: String,
    private val retryExecutor: Executor) : DataSource.Factory<String, 
RedditPost>() {
    val sourceLiveData = MutableLiveData<PageKeyedSubredditDataSource>()
    override fun create(): DataSource<String, RedditPost> {
        val source = PageKeyedSubredditDataSource(redditApi, subredditName, 
retryExecutor)
        sourceLiveData.postValue(source)
        return source
   }
}

在此代码示例中，'sourceLiveData' 发布活动数据源。反过来，数据源可以向视图公开所有相关信息，如网络状态和指示器（如果首次加载已完成）

为了添加刷新行为，使用 SwipeRefreshLayout 包裹回收器视图，如下所示。现在您可以访问数据源，您可以使它无效并且视图将被刷新

<androidx.swiperefreshlayout.widget.SwipeRefreshLayout android:id="@+id/swipe_refresh"
                                              android:layout_width="match_parent"
                                              android:layout_height="match_parent">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical"
        app:layoutManager="LinearLayoutManager"/>
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

分页库的进度条和错误消息

Progressbar and error message with Paging Library

android

android-architecture-components

android-paging