I don’ understand how can use navController and ch...

# compose

[Android75]

I don’ understand how can use navController and change scree/pager.
I have 3 screen @Ian Lake can you help me.
I need to change page and page is decide by viewModel
``````

[Ian Lake]

Put your code in a thread as per the pinned message: https://kotlinlang.slack.com/archives/CJLTWPH7S/p1616265877303000

[Android75]

@Composable
fun NavigationComponent(navController: NavHostController) {
    NavHost(
        navController = navController,
        startDestination = Destination.Splash.path
    ) {
        composable(Destination.Splash.path) {
            SplashScreen(navController)
        }
        composable(Destination.Dashboard.path) {
          
            DashboardScreen(navController)
        }
        composable(Destination.SectionPage.path+"/{type}") {backStackEntry ->
            SectionPage(navController, backStackEntry.arguments?.getString("type"))

        }
    }
}

Every screen receives navController and has its ViewModel.
ViewModel decides destination, of course.

@Composable
fun SplashScreen(navController: NavHostController) {
    val viewModel = hiltViewModel<SplashViewModel>()
     var splashScreenState = viewModel.uiState.collectAsState().value

ViewModel uses stateUi to change screen.

@HiltViewModel
class SplashViewModel @Inject constructor() : BaseViewModel() {
    val uiState = MutableStateFlow(SplashState())
    init {
        Handler(Looper.myLooper()!!).postDelayed({
            gotoDashBoard()
        }, 2000)
    }

    private fun gotoDashBoard() {

      uiSate.value = uiState.value.copy(
            navigate = Navigate(true, destination= NavigationItem.Dashboard)
        )
    }
}

In SplashSreen :

if(splashScreenState.navigate.change){
    navController.navigate(splashScreenState.navigate.destination.route)
}

ok.. i have a loop. I see Dashboard screen is recreated continuously.
I put this and works.. but i don’t like it

if(splashScreenState.navigate.change){ 
    splashScreenState.navigate.change= false
    navController.navigate(splashScreenState.navigate.destination.route)
}

[Android75]

I’d like follow MVVM pattern, ViewModel decides and sends to view state to change “page”

[Ian Lake]

You really didn't follow either of the other things I said

[Ian Lake]

Don't use Navigation for your splash screen - use the Splash screen APIs: https://kotlinlang.slack.com/archives/CJLTWPH7S/p1649050716032649?thread_ts=1649039860.384509&cid=CJLTWPH7S

[Ian Lake]

Don't call navigate as part of composition: https://kotlinlang.slack.com/archives/CJLTWPH7S/p1649051023852409?thread_ts=1649039860.384509&cid=CJLTWPH7S

[Android75]

ok viewModel doesn’t have a navController instance, i can’t use navigate inside composition so.. how and where i can put code to change screen? Ok for splashscreen but if in Dashboard has 3 buttons.. if i want follow MVVM, buttons send event to ViewModel and after ViewModel decides destination.. how can i change destination..

[ildar.i [Android]]

make a event SharedFlow, post events there from ViewModel, subscribe to it in LaunchedEffect and you’re good to go - you can navigate anywhere from LaunchedEffect

[Android75]

as this code

LaunchedEffect(Unit) {
    viewModel.someUIState.collect { uiState -> 
        when(uiState) {
            // Same as in the question
        }
    }
}

[Android75]

ok it works but when from Page2 use a navController.popBackStack() Page1 has the State with navigation to Page2 so i can’t back

[Android75]

LaunchedEffect(uiState) {

        if(uiState.destination.isNotEmpty()) {
            navController.navigate(uiState.destination)
        }

}

DisposableEffect(LocalLifecycleOwner.current) {
    onDispose {
        viewModel.resetState()
    }
}

[ildar.i [Android]]

Use SharedFlow instead of StateFlow

[gildor]

@Android75 A side note about your message. I think it’s not nice to ask in a public channel and mention particular person to help you the same time. It’s not twitter.
It may be inconvenient for this person to be essentially obligated to answer you and it also discourages other to give you advice
It’s my personal opinion, not like a moderator

[ildar.i [Android]]

While I agree with you, but as a person with two ignored questions I can undestand him)

[gildor]

Well there is probably a reason for this. It’s not a free service of support, nobody obligated to answer you, but it puts those “obligations” to answer if you ping someone specific

[Android75]

Sorry, but i ping Ian lake because yiou help me last conversation about navigation.. i apologize