android - fragment popbackstack 触发生命周期范围收集

Question

情况
我提交数据setTripDeliver ，收集工作正常(触发加载，然后成功)。我按下一个按钮转到下一个 fragment B(使用 replace )。之后，我按下返回按钮(使用 popbackstack )。收集成功触发。
相关代码
这些代码位于 FragmentA.kt里面 onViewCreated .

private fun startLifeCycle() {
    viewLifecycleOwner.lifecycleScope.launch {
        viewLifecycleOwner.lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
            launch {
                collectTripDeliver()
            }
            launch {
                collectTripReattempt()
            }
        }
    }
}

这些代码何时在按钮上提交数据 setOnClickListener .

viewLifecycleOwner.lifecycleScope.launchWhenStarted {
    viewModel.setTripDeliver(
         verificationCode,
         remark
    )
}

收集流量的方法 collectTripReattempt()

private suspend fun collectTripReattempt() {
        viewModel.tripReattempt.collect {
            when (it) {
                is Resource.Initialize -> {

            }
            is Resource.Loading -> {
                Log.i("???","collectTripReattempt loading")
                handleSaveEarly()
            }
            is Resource.Success -> {
                val error = it.data?.error
                if (error == null) {
                    Tools.showToast(requireContext(), "Success Reattempt")
                    Log.i("???","collectTripReattempt Success")
             
                } else {
                    Tools.showToast(requireContext(), "$error")
                }
                handleSaveEnding()
            }
            is Resource.Error -> {
                handleSaveEnding()
            }
        }
    }
}

以下代码来自 ViewModel .

private val _tripDeliver =
    MutableStateFlow<Resource<TripDeliverResponse>>(Resource.Initialize())
val tripDeliver: StateFlow<Resource<TripDeliverResponse>> = _tripDeliver

此方法调用存储库。

suspend fun setTripDeliver(
    verificationCode: String?,
    remark: String?
) {
    _tripDeliver.value = Resource.Loading()
    try {
        val result = withContext(ioDispatcher) {
            val tripDeliverParameter = DeliverParameter(
                verificationCode,
                remark
            )
            val response = appRepository.setTripDeliver(tripDeliverParameter)
            Resource.getResponse { response }
        }
        _tripDeliver.value = result
    } catch (e: Exception) {
        when (e) {
            is IOException -> _tripDeliver.value =
                Resource.Error(messageInt = R.string.no_internet_connection)
            else -> _tripDeliver.value =
                Resource.Error("Trip Deliver Error: " + e.message)
        }
    }
}

日志猫

2021-07-09 19:56:10.946 7446-7446/com.package.app I/???: collectTripReattempt loading
2021-07-09 19:56:11.172 7446-7446/com.package.app I/???: collectTripReattempt Success
2021-07-09 19:56:17.703 7446-7446/com.package.app I/???: collectTripReattempt Success

如您所见，最后一个 Success在我按下返回按钮后再次调用 ( popbackstack)
问题
如何让它只触发一次？是我实现它的方式不对吗？先感谢您。

Answer 1

这不是您的实现的问题，这是因为 stateIn() 您的 viewModel 中使用了哪些将常规流量转换为 stateFlow如果根据您的代码 fragment 再次触发成功，那么为什么不触发加载？
根据文章，它显示 latest cached value当您离开屏幕并返回时，您会看到最新的缓存值。
资源:
https://medium.com/androiddevelopers/migrating-from-livedata-to-kotlins-flow-379292f419fbThe latest value will still be cached so that when the user comes back to it, the view will have some data immediately.