Stateflow 在 reyclerview android kotlin 中引用整个数据

嘿嘿我正在学习状态流在 Android 科特林中。我正在创建一个反向对话日历视图回收者视图. In my mainactivity有一个fragment，里面有我reyclerview。我的目标是做分页的东西 in my 回收者视图所以我先加载几个月，然后在我的回收视图中添加越来越多的数据answer。我成功地实现了它。但问题是当我到达临界点并触发新数据。我的整个列表已刷新，但未更新，而是删除了以前的数据。我不明白为什么会发生这种情况可变状态流而且我也是这方面的新手flow. My Github项目链接在这里。请指导我在这里做错了什么。我的目标是预先添加 stateFlow 数据。谢谢

对话片段.kt

class ConversationFragment(val customManager: CustomManager) : Fragment() {

    companion object {
        private const val DATA = "data"
        fun create(
            data: List<ConversationDate>,
            customManager: CustomManager
        ): ConversationFragment {
            val fragment = ConversationFragment(customManager)
            val bundle = Bundle()
            bundle.putParcelableArrayList(
                DATA,
                ArrayList<Parcelable>(data)
            )
            fragment.arguments = bundle
            return fragment
        }
    }

    private var _binding: ConversationFragmentLayoutBinding? = null
    private val binding get() = _binding!!
    private val visibleThreshold = 7
    private var previousTotalItemCount = 0
    private var loading = true
    private val weeklyAdapter = ConversationWeeklyAdapter()
    private val viewModel by viewModels<FragmentViewModel>()

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        setupViewModel()
        _binding = ConversationFragmentLayoutBinding.inflate(inflater, container, false)
        setupView()
        return binding.root
    }

    private fun setupViewModel() {
        viewModel.data = arguments?.getParcelableArrayList(DATA)
        viewModel.startDate = customManager.startDate()
        viewModel.endDate = customManager.endDate()
    }

    private fun setupView() {
        viewModel.weeklyFormatData()

        activity?.lifecycleScope?.launchWhenCreated {
            activity?.repeatOnLifecycle(Lifecycle.State.CREATED) {
                viewModel.prepareMutableStateFlow.collectLatest {
                    weeklyAdapter.submitList(it)
                }
            }
        }

        binding.conversationView.apply {
            adapter = weeklyAdapter
            layoutManager = LinearLayoutManager(context).apply {
                orientation = LinearLayoutManager.HORIZONTAL
                stackFromEnd = true
            }

            addOnScrollListener(object : RecyclerView.OnScrollListener() {

                override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                    super.onScrolled(recyclerView, dx, dy)
                    val firstVisibleItemPosition =
                        (recyclerView.layoutManager as LinearLayoutManager).findFirstVisibleItemPosition()
                    val totalItemCount = recyclerView.adapter?.itemCount

                    if (totalItemCount != null) {
                        if (totalItemCount < previousTotalItemCount) {
                            previousTotalItemCount = totalItemCount
                            if (totalItemCount == 0) {
                                loading = true
                            }
                        }
                    }

                    if (totalItemCount != null) {
                        if (loading && (totalItemCount > previousTotalItemCount)) {
                            loading = false
                            previousTotalItemCount = totalItemCount
                        }
                    }

                    if (!loading && firstVisibleItemPosition < visibleThreshold) {
                        customManager.loadMoreData()
                        loading = true
                    }

                }
            })
        }

    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

    fun loadMoreData(item: List<ConversationDate>) {
        viewModel.startDate =
            SimpleDateFormat("yyyy-MM-dd", Locale.getDefault()).parse("2021-11-01")
        viewModel.endDate =
            SimpleDateFormat("yyyy-MM-dd", Locale.getDefault()).parse("2021-11-30")
        val previousData = viewModel.data
        if (previousData != null) {
            viewModel.data = previousData + item
        }
        viewModel.weeklyFormatData()
    }
}

FragmentViewModel.kt

class FragmentViewModel(app: Application) : AndroidViewModel(app) {

    var data: List<ConversationDate>? = null
    var startDate: Date? = null
    var endDate: Date? = null
    private val dateRange: MutableList<Date>
        get() {
            val datesInRange = mutableListOf<Date>()
            val tempCalendar = Calendar.getInstance()
            tempCalendar.time = startDate as Date
            while (tempCalendar.time <= endDate) {
                datesInRange.add(tempCalendar.time)
                tempCalendar.add(Calendar.DATE, 1)
            }
            return datesInRange
        }
    val prepareMutableStateFlow: MutableStateFlow<List<ConversationCount>> =
        MutableStateFlow(emptyList())

    fun weeklyFormatData() {
        val conversationCount = mutableListOf<ConversationCount>()
        viewModelScope.launch {
            dateRange.forEachIndexed { index, dateRangeValue ->
                val findData = data?.find {
                    dateRangeValue == it.dateObject
                }
                conversationCount.add(
                    ConversationCount(
                        setDay(dateRangeValue),
                        index,
                        findData != null
                    )
                )
            }
            prepareMutableStateFlow.value = conversationCount
        }
    }

    private fun setDay(date: Date): String? {
        return SimpleDateFormat("dd", Locale.getDefault()).format(date)
    }
}

我的模拟 API 响应link

问题描述

加载应用程序时，将出现片段屏幕并显示一些日期。我设置开始日期 as 2021-12-01 and endDate截至今天日期，即2022-01-13。因此，当开始滚动并达到加载更多数据的阈值时。我通过了比开始日期 as 2021-11-01 and endDate as 2021-11-30。它已添加到列表中，但以前的数据已被删除。我不明白为什么会发生这种情况。我正在附上我的 YouTubelink

这是大量的代码需要完成，我无法弄清楚你想要做的一切。你没有表现出什么CustomManager.loadMoreData()做。但我假设这是一个当您滚动到底部时会加载其他项目的列表？如果您逐步了解以下逻辑onScrolled功能，好像没有什么意义。就像为什么会totalItemCount永远小于previousTotalItemCount?

如果您向下滚动到@明阮对您链接的问题的回答，这是一个更简单的解决方案。我会更进一步，创建一个辅助类，以便您可以保持片段代码干净。我添加了一项功能，当新数据到达适配器时，它会自动注册以重置自身。注意，我还没有测试过这个课程！

class BottomReachedListener(
    var onBottomReached: () -> Unit = {}
) : RecyclerView.OnScrollListener() {
    private var isTriggered = false
    private var registeredAdapter: RecyclerView.Adapter<*>? = null
    private val observer = object: RecyclerView.AdapterDataObserver() {
        override fun onChanged() = reset()
    }
    
    fun reset() {
        isTriggered = false
    }

    override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
        if (isTriggered) {
            return
        }
        val layoutManager = recyclerView.layoutManager as? LinearLayoutManager
            ?: error("No LinearLayoutManager")
        val totalItems = layoutManager.itemCount
        val lastVisibleItem = layoutManager.findLastVisibleItemPosition()

        if (lastVisibleItem == totalItems - 1) {
            registerWithAdapter(recyclerView)
            isTriggered = true
            onBottomReached()
        }
    }

    private fun registerWithAdapter(recyclerView: RecyclerView) {
        registeredAdapter?.unregisterAdapterDataObserver(observer)
        registeredAdapter = recyclerView.adapter
        registeredAdapter?.registerAdapterDataObserver(observer)
    }
}

现在，在您的 Fragment 中，您需要做的就是将此类的实例设置为滚动侦听器，并向其传递一个回调，以在需要加载新数据时调用：

addOnScrollListener(BottomReachedListener {
    customManager.loadMoreData() // for example
})

不知道你的下游逻辑是否还有其他问题。如果没有实际的应用程序进行调试并了解其应该执行的所有操作，则代码太多，无法推理。