用于 fragment 中状态流的 Android 通用函数

Question

我在我的应用程序和我的 Fragment 中使用 StateFlow 我用它来 -

private var job: Job? = null

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        job = lifecycleScope.launchWhenResumed {
            viewModel.getData().collect {
                // ...
            }
        }
    }

    override fun onPause() {
        job?.cancel()
        super.onPause()
    }

如您所见，我在 onPause 中取消了作业。我如何使用通用函数以避免在每个 fragment 中执行 job?.cancel。

我不想使用 BaseFragment

Answer 1

一个简单的解决方案是利用 fragment 生命周期在暂停时自动取消作业。

fun CoroutineScope.launchUntilPaused(lifecycleOwner: LifecycleOwner, block: suspend CoroutineScope.() -> Unit){
    val job = launch(block = block)
    lifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver {
        override fun onPause(owner: LifecycleOwner) {
            job.cancel()
            lifecycleOwner.lifecycle.removeObserver(this)
        }
    })
}

//Usage
class MyFragment: Fragment() {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        lifecycleScope.launchUntilPaused(this){
            someFlow.collect{
                ...
            }
        }
    }
}

如果每个 fragment 有许多这样的作业，我建议改用自定义 CoroutineScope，以避免激活许多生命周期观察器。

class CancelOnPauseScope(lifecycleOwner: LifecycleOwner): CoroutineScope by MainScope(){
    init{
        lifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver{
            override fun onPause(owner: LifecycleOwner) {
                cancel()
                lifecycleOwner.lifecycle.removeObserver(this)
            }
        })
    }
}

class MyFragment: Fragment() {
    private val scope = CancelOnPauseScope(this)
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        scope.launch{
            someFlow.collect{
                ...
            }
        }
    }
}