如何在组合导航中处理类似于 onActivityResult 的行为？

Question

我有一个设置，我想导航到结果的可组合项，然后根据该结果我想从父项启动另一个可组合项。这是设置

ScreenA 为结果启动 Screen B（用户在 screenB 中做某事）-> ScreenB 设置结果并从堆栈中弹出自身-> ScreenA 查看结果并根据值启动 ScreenC。

这里的问题是，一旦 ScreenB 设置了结果，我在结果上设置的观察器就会无限发射。

这是我的设置的简化版本：

fun AppNavHost(
    navController: NavHostController
) {
    NavHost(
        navController = navController,
        startDestination = "ScreenA",
    ) {
        composable("ScreenA") {
            ScreenA(
                onClick = {
                    navController.navigate("ScreenB")
                }
            )
            val result = navController.currentBackStackEntry
                ?.savedStateHandle
                ?.getLiveData<String>("key")
                ?.observeAsState()
            result?.value?.let { str ->
                // This seems to not remove the key or at least
                // the live data value is not nulled out
                navController.currentBackStackEntry
                    ?.savedStateHandle
                    ?.remove<String>("key")
                if (str == "result") {
                    // This condition hits infinitely
                    navController.navigate("ScreenC")
                    // This logs infinitely
                    Log.d("TAG", "found result: $str")
                }
            }
        }
        composable("ScreenB") {
            ScreenB(
                onClick = {
                    navController.previousBackStackEntry
                        ?.savedStateHandle
                        ?.set("key", "result")
                    navController.popBackStack()
                }
            )
        }
        composable("ScreenC") { ScreenC() }
    }
}

我已经看过并且我这里的设置是相似的。如何修复此行为，使 ScreenB 的结果只被读取一次？

Answer 1

使用 LaunchedEffect 避免在重新合成级别多次调用导航。

NavHost(
    navController = navController,
    startDestination = "ScreenA",
) {
    composable("ScreenA") {
        Button(
            onClick = {
                navController.navigate("ScreenB")
            },
            modifier = Modifier.padding(16.dp)
        ) {
            Text("Go to Screen B")
        }
        val result = navController.currentBackStackEntry
            ?.savedStateHandle
            ?.getLiveData<String>("key")
            ?.observeAsState()
        result?.value?.let { str ->
            navController.currentBackStackEntry
                ?.savedStateHandle
                ?.remove<String>("key")
            LaunchedEffect(str) {
                if (str == "result") {
                    navController.navigate("ScreenC")
                    Log.d("TAG", "found result: $str")
                }
            }
        }
    }
    composable("ScreenB") {
        Button(
            onClick = {
                navController.previousBackStackEntry
                    ?.savedStateHandle
                    ?.set("key", "result")
                navController.popBackStack()
            }
        ) {
            Text("Screen B")
        }
    }
     composable("ScreenC") { ScreenC() }
}

如何在组合导航中处理类似于 onActivityResult 的行为？

How to handle behavior similar to onActivityResult in compose navigation?

android

android-jetpack-compose

jetpack-compose-navigation