Jetpack Compose 导航结果

Question

I'm using the Jetpack Navigation library with the Compose version. I'm setting up navigation like it's shown here

I want to be able to navigate from screen A to screen B. Once B does something and pops off the back stack, it will then return a result that screen A can access.

I found a way to do this using Activities here but I want to avoid creating any extra activities and do this in compose.

Answer 1

From the Composable that you want to return data, you can do the following:

navController.previousBackStackEntry
    ?.savedStateHandle
    ?.set("your_key", "your_value")
navController.popBackStack()

and then, from the source Composable, you can listen for changes using a LiveData .

val secondScreenResult = navController.currentBackStackEntry
    ?.savedStateHandle
    ?.getLiveData<String>("your_key")?.observeAsState()
...
secondScreenResult?.value?.let {
    // Read the result
}

Answer 2

If you need only once get value, you need remove value after usage:

val screenResultState = navController.currentBackStackEntry
    ?.savedStateHandle
    ?.getLiveData<String>("some_key")?.observeAsState()

screenResultState?.value?.let {
    ...
    // make something, for example `viewModel.onResult(it)`
    ...
    //removing used value
    navController.currentBackStackEntry
        ?.savedStateHandle
        ?.remove<String>("some_key")
}

I also extract it in function (for JetPack Compose)

@Composable
fun <T> NavController.GetOnceResult(keyResult: String, onResult: (T) -> Unit){
    val valueScreenResult =  currentBackStackEntry
        ?.savedStateHandle
        ?.getLiveData<T>(keyResult)?.observeAsState()

    valueScreenResult?.value?.let {
        onResult(it)
       
        currentBackStackEntry
            ?.savedStateHandle
            ?.remove<T>(keyResult)
    }
}

you can copy it to your project and use like this:

navController.GetOnceResult<String>("some_key"){
    ...
    // make something
}

Answer 3

for jetpack compose you must use Flow with collectAsState for get result:

navController.currentBackStackEntry
?.savedStateHandle?.getStateFlow<Boolean?>("refresh", false)
?.collectAsState()?.value?.let {
if (it)screenVM.refresh() }

also you can remove Entry with add this after screenVM.refresh() :

 navController.currentBackStackEntry
                ?.savedStateHandle ?.set("refresh", false)

Answer 4

You can get the result without a LiveData or a Flow, you can use savedStateHandle.remove method. I think this is the easier way:

val secondResult = appNavController.currentBackStackEntry?.savedStateHandle?.remove<Data?>("data")
secondResult?.let { data ->
    Log.d(TAG, "Data result: $data")
}

Answer 5

add dependency

implementation "androidx.compose.runtime:runtime-livedata:$compose_version"

On the Sender screen set a key value pair to send back to the caller screen, I use a Boolean with key name of "key" value true

navController.previousBackStackEntry?.savedStateHandle?.set("key", true)

navigate up

navController.navigateUp()

The receiver screen (caller) listens to the results and then remove it:

 val result =  navController.currentBackStackEntry?.savedStateHandle
    ?.getLiveData<Boolean>("key")?.observeAsState()
result?.value?.let {
    navController.currentBackStackEntry?.savedStateHandle
        ?.remove<Boolean>("key")
}

First Screen

@Composable fun FirstScreen(navController: NavController){

val result =  navController.currentBackStackEntry?.savedStateHandle
    ?.getLiveData<Boolean>("key")?.observeAsState()
result?.value?.let {
    navController.currentBackStackEntry?.savedStateHandle
        ?.remove<Boolean>("key")
}

Button(onClick = {
    navController.navigateUp("secondScreen")
}) {
    "Open second screen"
}}

Answer 6

val navController = rememberNavController()
composable("A") {
    val viewmodel: AViewModel = hiltViewModel()
    AScreen()
}
composable("B") {
    val viewmodel: BViewModel = hiltViewModel()
    val previousViewmodel: AViewModel? = navController
        .previousBackStackEntry?.let {
            hiltViewModel(it)
        }
    BScreen(
       back = { navController.navigateUp() },
       backWhitResult = { arg ->
           previousViewmodel?.something(arg)
       }
    )
}