从 launchWhenStarted 调用多个视图模型方法不起作用

问题描述

这段代码在同一个视图模型上调用两个方法并监听更新。但是只有第一个方法完成，第二个没有事件触发。

private fun initData() {
    lifecycleScope.launchWhenStarted {
        viewmodel.incrementCount().collect {
            info { "Count: $it" }
        }

        viewmodel.getAllTeams().collect {
            when (it) {
                is State.Success -> {
                    info { "Got teams with size: ${it.result}.size" }
                }
                is State.Error -> {
                    info { "Error getting teams: ${it.message}" }
                }
                State.Loading -> {
                    info { "Loading all teams" }
                }
            }
        }
    }
}

视图模型

class Dashboardviewmodel : viewmodel(),com.droid.common.Logger {

fun incrementCount(): MutableStateFlow<Int> {
    val countState = MutableStateFlow(0)

    viewmodelScope.launch {
        repeat(5) {
            countState.value = (it)
            delay(1000)
        }
    }

    return countState
}

fun getAllTeams(): MutableStateFlow<State> {
    val state = MutableStateFlow<State>(State.None)

    state.value = State.Loading

    viewmodelScope.launch {
        try {
            val allTeams = Footballapiclient.apiService.getAllTeams()
            state.value = State.Success(allTeams)
        } catch (exception: Exception) {
            error { "Error getting all teams: ${exception.message}" }
            state.value = State.Error(exception.message.toString())
        }
    }

    return state
}

但是，使用单独的生命周期范围调用它们是可行的

private fun initData() {
    lifecycleScope.launchWhenStarted {
        viewmodel.incrementCount().collect {
            info { "Count: $it" }
        }
    }

    lifecycleScope.launchWhenStarted {
        viewmodel.getAllTeams().collect {
            when (it) {
                is State.Success -> {
                    info { "Got teams with size: ${it.result}.size" }
                }
                is State.Error -> {
                    info { "Error getting teams: ${it.message}" }
                }
                State.Loading -> {
                    info { "Loading all teams" }
                }
            }
        }
    }
}

我似乎无法理解这种行为，有人知道为什么吗？

解决方法

您将需要不同的协程，因为 collect() 是一个挂起函数，它会挂起直到您的 Flow 终止。

launchWhenStarted 的问题在于，虽然您新发出的项目不会被处理，但您的生产者仍会在后台运行。

对于收集多个流，目前推荐的方法是：

lifecycleScope.launch {
    lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
        launch {
          viewModel.incrementCount().collect { ... }   
        }
    
        launch {
            viewModel.getAllTeams().collect { ... }
        }
    }
}