Paging3：从其他片段返回时，在适配器上调用refresh不会触发刷新

问题描述

我正在为我的应用程序使用最新的Paging3库，该库具有显示照片列表的图库屏幕，以及显示照片更多选项和信息的详细信息屏幕。我已将图片库设置为在片段的onCreate中获取照片列表：

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // display all photos,sorted by latest
        viewmodel.getAllPhotos()
    }

如果成功，则照片将通过submitList传递到适配器，并且如果用户拉下图库屏幕，则应该触发刷新，因此我已相应地设置了refreshListener。我在onViewCreated上执行此操作（请注意，我使用ViewBinding）：

    override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
        super.onViewCreated(view,savedInstanceState)
        binding = FragmentgalleryBinding.bind(view)

        viewLifecycleOwner.lifecycle.addobserver(viewmodel)

        setupgallery()

        setupRetryButton()
    }

    private fun setupgallery() {
        // Add a click listener for each list item
        adapter = galleryAdapter{ photo ->
            photo.id.let {
                findNavController().navigate(galleryFragmentDirections.detailsAction(it))
            }
        }

        viewmodel.uiState?.observe(viewLifecycleOwner,{
            binding?.swipeLayout?.isRefreshing = false
            adapter.submitData(lifecycle,it)
        })

        binding?.apply {
            // Apply the following settings to our recyclerview
            list.adapter = adapter.withLoadStateHeaderAndFooter(
                header = RetryAdapter {
                    adapter.retry()
                },footer = RetryAdapter {
                    adapter.retry()
                }
            )

            // Add a listener for the current state of paging
            adapter.addLoadStateListener { loadState ->
                Log.d("galleryFragment","LoadState: " + loadState.source.refresh.toString())
                // Only show the list if refresh succeeds.
                list.isVisible = loadState.source.refresh is LoadState.NotLoading
                // do not show SwipeRefreshLayout's progress indicator if LoadState is NotLoading
                swipeLayout.isRefreshing = loadState.source.refresh !is LoadState.NotLoading
                // Show loading spinner during initial load or refresh.
                progressBar.isVisible = loadState.source.refresh is LoadState.Loading && !swipeLayout.isRefreshing
                // Show the retry state if initial load or refresh fails.
                retryButton.isVisible = loadState.source.refresh is LoadState.Error

                val errorState = loadState.source.append as? LoadState.Error
                    ?: loadState.source.prepend as? LoadState.Error
                    ?: loadState.append as? LoadState.Error
                    ?: loadState.prepend as? LoadState.Error
                errorState?.let {
                    swipeLayout.isRefreshing = false
                    Snackbar.make(requireView(),"\uD83D\uDE28 Wooops ${it.error}",Snackbar.LENGTH_LONG).show()
                }
            }

            swipeLayout.apply {
                setonRefreshListener {
                    isRefreshing = true
                    adapter.refresh()
                }
            }
        }

在第一次加载时，下拉布局会成功触发刷新。但是，在导航到详细信息屏幕后会出现问题。在详细信息屏幕上，按返回按钮可将用户返回画廊。如果用户拉出布局，则会显示进度指示器，但不会发生adapter.refresh()。我不知道如何调试它。

作为参考，这是我负责抓取照片的viewmodel的样子：

class galleryviewmodel(private val getAllPhotosUseCase: GetAllPhotosUseCase): Baseviewmodel() {

    private val _uiState = mutablelivedata<PagingData<UnsplashPhoto>>()
    val uiState: LiveData<PagingData<UnsplashPhoto>>? get() = _uiState

    fun getAllPhotos() {
        compositedisposable += getAllPhotosUseCase.getAllPhotos()
            .cachedIn(viewmodelScope)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeBy(
                onNext = { _uiState.value = it },onError = {
                    it.printstacktrace()
                }
            )
    }

}

GetAllPhotosUseCase将getAllPhotos调用转发到包含以下内容的Repository实现：

class UnsplashRepoImpl(private val unsplashApi: UnsplashApi): UnsplashRepo {

    override fun getAllPhotos(): Observable<PagingData<UnsplashPhoto>> = Pager(
        config = PagingConfig(Const.PAGE_SIZE),remoteMediator = null,// Always create a new UnsplashPagingSource object. Failure to do so would result in a
        // IllegalStateException when adapter.refresh() is called--
        // Exception message states that the same PagingSource was used as the prev request,// and a new PagingSource is required
        pagingSourceFactory = { UnsplashPagingSource(unsplashApi) }
    ).observable

....
}

我的RxPagingSource的设置如下：

class UnsplashPagingSource (private val unsplashApi: UnsplashApi)
    : RxPagingSource<Int,UnsplashPhoto>(){

    override fun loadSingle(params: LoadParams<Int>): Single<LoadResult<Int,UnsplashPhoto>> {
        val id = params.key ?: Const.PAGE_NUM
        return unsplashApi.getAllPhotos(id,Const.PAGE_SIZE,"latest")
        .subscribeOn(Schedulers.io())
            .map { response ->
                response.map { it.toUnsplashPhoto() }
            }
            .map<LoadResult<Int,UnsplashPhoto>> { item ->
                LoadResult.Page(
                    data = item,prevKey = if (id == Const.PAGE_NUM) null else id - 1,nextKey =  if (item.isEmpty()) null else id + 1
                )
            }
            .onErrorReturn { e -> LoadResult.Error(e) }
    }
}

有人可以以此指向我正确的方向吗？

编辑：正如Jay Dangar所说，将viewmodel.getAllPhotos()移至onResume将使对adapter.refresh()的调用成功触发。但是，我不想每次从详细信息屏幕导航到图库时都获取所有照片。为避免这种情况，我在拉布局时不调用adapter.refresh()，而是调用viewmodel.getAllPhotos()。

我仍然不明白为什么接受的答案有效，但是我认为adapter.refresh()仅在创建新的PagingSource或其他功能时有效。

解决方法

将您的引荐逻辑放入onResume（）而不是onCreate（）中，这是生命周期管理的问题。