State restoration

The Screen interface is Serializable. Every param of your screens will be saved and restored automatically. Because of that, it's important to know what can be passed as param: anything that can be stored inside a Bundle.
// ✔️ DO
@Parcelize
data class Post(/*...*/) : Parcelable
​
data class ValidScreen(
    val userId: UUID, // Built-in serializable types
    val post: Post // Your own parcelable and serializable types
) : Screen {
    // ...
}
​
// 🚫 DON'T
class Post(/*...*/)
​
data class InvalidScreen(
    val context: Context, // Built-in non-serializable types
    val post: Post // Your own non-parcelable and non-serializable types
) : Screen {
    // ...
}
Not only the params, but the properties will also be restored, so the same rule applies.
// ✔️ DO
class ValidScreen : Screen {
    
    // Serializable properties
    val tag = "ValidScreen"
    
    // Lazily initialized serializable types
    val randomId by lazy { UUID.randomUUID() }
​
    // Lambdas
    val callback = { /*...*/ }
}
​
// 🚫 DON'T
class InvalidScreen : Screen {
​
    // Non-serializable properties
    val postService = PostService()
}
If you want to inject dependencies through a DI framework, make sure it supports Compose, like Koin and Kodein.
// ✔️ DO
class ValidScreen : Screen {
    
    @Composable
    override fun Content() {
        // Inject your dependencies inside composables
        val postService = get<PostService>()
    }
}
​
// 🚫 DON'T
class InvalidScreen : Screen {
​
    // Using DI to inject non-serializable types as properties
    val postService by inject<PostService>()
}
Identifying screens
The Screen interface has a key property used for saving and restoring the states for the subtree. You can override the default value to set your own key.
class HomeScreen : Screen {
​
    override val key = "CUSTOM_KEY"
​
    @Composable
    override fun Content() {
        // ...
    }
}
Voyager provides a uniqueScreenKey property, useful if you don't want to manage the keys yourself.
override val key = uniqueScreenKey
You should always set your own key if the screen:
Is used multiple times in the same Navigator
Is an anonymous or local class
Stack API
Transitions
Last modified 1yr ago