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我正在为我的应用程序使用最新的 Paging3 库，它有一个显示照片列表的画廊屏幕，以及一个显示更多选项和照片信息的详细信息屏幕。我已经设置画廊来获取我的片段中的照片列表onCreate：

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

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

如果成功，照片会通过 传递给适配器submitList，如果用户拉下画廊屏幕，它应该会触发刷新，所以我refreshListener相应地设置了一个。我这样做onViewCreated（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()
                }
            }
        }

首次加载时，下拉布局会成功触发刷新。但是，在我导航到详细信息屏幕后出现问题。在详细信息屏幕中，按返回按钮可将用户返回到图库。如果用户拉动布局，进度指示器会出现但adapter.refresh()不会发生。我不知道如何调试它。

作为参考，这是我ViewModel负责获取照片的人员的样子：

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()
                }
            )
    }

}

将调用GetAllPhotosUseCase转发到包含以下内容的实现：getAllPhotosRepository

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RxPagingSource的设置是这样的：

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) }
    }
}

谁能指出我正确的方向？

编辑：正如 Jay Dangar 所说，移动viewModel.getAllPhotos()到onResume会adapter.refresh()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。为了避免这种情况，我不调用adapter.refresh()布局时调用，而是调用viewModel.getAllPhotos()。

我仍然不明白为什么接受的答案有效，但我认为adapter.refresh()只有在PagingSource创建新答案或其他东西时才有效。

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1 回答 1

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

于 2020-09-21T03:49:46.627 回答