Question

我想在composable-function的回调中调用暂停功能。

suspend fun getLocation(): Location? { /* ... */ }

@Composable
fun F() {

    val (location, setLocation) = remember { mutableStateOf<Location?>(null) }

    val getLocationOnClick: () -> Unit = {
        /* setLocation __MAGIC__ getLocation */
    }

    Button(onClick = getLocationOnClick) {
        Text("detectLocation")
    }

}

如果我会使用Rx，那么我可以subscribe。

我可以先做invokeOnCompletion，然后再做getCompleted，但该API是试验性的。

我不能在launchInComposition中使用getLocationOnClick，因为launchInComposition是@Composable，而getLocationOnClick不能是@Composable。

在@Composable函数内部的常规函数中获取悬挂函数结果的最佳方法是什么？

Answer 1

创建与可组合对象生命周期相关联的协程范围，并使用该范围调用您的暂停函数

suspend fun getLocation(): Location? { /* ... */ }

@Composable
fun F() {
    // Returns a scope that's cancelled when F is removed from composition
    val coroutineScope = rememberCoroutineScope()

    val (location, setLocation) = remember { mutableStateOf<Location?>(null) }

    val getLocationOnClick: () -> Unit = {
        coroutineScope.launch {
            val location = getLocation()
        }
    }

    Button(onClick = getLocationOnClick) {
        Text("detectLocation")
    }
}

Answer 2

您可以使用ViewModel的viewModelScope或任何其他协程范围。

从LazyColumnFor中删除项目的操作示例，该操作需要由ViewModel处理的暂停调用。

spark-shell

Answer 3

这对我有用：

@Composable
fun TheComposable() {

    val coroutineScope = rememberCoroutineScope()
    val (loadResult, setLoadResult) = remember { mutableStateOf<String?>(null) }

    IconButton(
        onClick = {
            someState.startProgress("Draft Loading...")
            coroutineScope.launch {
                withContext(Dispatchers.IO) {
                    try {
                        loadResult = DataAPI.getData() // <-- non-suspend blocking method
                    } catch (e: Exception) {
                        // handle exception
                    } finally {
                        someState.endProgress()
                    }
                }
            }

        }
    ) {
        Icon(Icons.TwoTone.Call, contentDescription = "Load")
    }

我还尝试了以下辅助函数，以强制开发同事处理异常并最终清理状态（也使相同的代码（也许！？）更短一些，（也许！？）更具可读性):

fun launchHelper(coroutineScope: CoroutineScope,
                 catchBlock: (Exception) -> Unit,
                 finallyBlock: () -> Unit,
                 context: CoroutineContext = EmptyCoroutineContext,
                 start: CoroutineStart = CoroutineStart.DEFAULT,
                 block: suspend CoroutineScope.() -> Unit
): Job {
    return coroutineScope.launch(context, start) {
        withContext(Dispatchers.IO) {
            try {
                block()
            } catch (e: Exception) {
                catchBlock(e)
            } finally {
                finallyBlock()
            }
        }
    }
}

这里是如何使用该辅助方法：

@Composable
fun TheComposable() {

    val coroutineScope = rememberCoroutineScope()
    val (loadResult, setLoadResult) = remember { mutableStateOf<String?>(null) }

    IconButton(
        onClick = {
            someState.startProgress("Draft Loading...")
            launchHelper(coroutineScope,
                catchBlock = { e -> myExceptionHandling(e) },
                finallyBlock = { someState.endProgress() }
            ) {
                loadResult = DataAPI.getData() // <-- non-suspend blocking method
            }

        }
    ) {
        Icon(Icons.TwoTone.Call, contentDescription = "Load")
    }

}

如何在可组合函数回调中调用Kotlin协程？

3 个答案: