ScreenModel

The ScreenModel API is a part of the modulecafe.adriel.voyager:voyager-screenmodel (see Setup).

ScreenModel is just like a ViewModel: designed to store and manage UI-related data in a lifecycle conscious way. It also allows data to survive configuration changes such as screen rotations.

Unlike ViewModel, ScreenModel is just an interface. It's also Android independent and doesn't requires an Activity or Fragment to work.

class HomeScreenModel : ScreenModel {
   
   // Optional
    override fun onDispose() {
        // ...
    }
}

ScreenModel is integrated with Coroutines, RxJava, LiveData, Koin, Kodein and Hit!

By design, it's only possible to create a ScreenModel instance inside a Screen. Call rememberScreenModel and provide a factory lambda.

class HomeScreen : Screen {

    @Composable
    override fun Content() {
        val screenModel = rememberScreenModel { HomeScreenModel() }
        // ...
    }
}

If you need to have multiple instances of the same ScreenModel for the same Screen, add a tag to differentiate them.

val screenModel = rememberScreenModel(tag = "CUSTOM_TAG") { HomeScreenModel() }

Sample

Source code here.

Navigator scoped ScreenModel

TherememberNavigatorScreenModel are part of the navigator library.

Starting from 1.0.0rc08 by using the new Navigator extension called rememberNavigatorScreenModel is possible to have a ScreenModel that is shared cross all Screens from a Navigator and when the Navigator leaves the Composition the ScreenModel is disposed.

class HomeScreen : Screen {

    @Composable
    override fun Content() {
        val navigator = LocalNavigator.currentOrThrow
        val screenModel = navigator.rememberNavigatorScreenModel { HomeScreenModel() }
        // ...
    }
}

Each DI library we provide a extension out of the box it is also provided support for Navigator scoped ScreenModel. See Koin, Kodein and Hit!