AnimatedNavDecorator

AnimatedNavDecorator is used by AnimatedNavDecoration as a way to provide hooks into its AnimatedContent, allowing for custom navigation animations.

This interface allows you to define how the content of a navigation destination should appear and animate when navigated to. It provides hooks into key moments of the navigation transition process, enabling a high degree of customization.

Usage

Implement transitionSpec

• Provide a ContentTransform instance. This defines the default transition behavior used when no other override is provided.

Implement targetState

• This is called to create an AnimatedNavState object for the incoming navigation destination.

• It should use the provided args and backStackDepth to construct an instance of a custom AnimatedNavState that represents the target state of the navigation.

Implement updateTransition

• This is responsible for setting up and updating the Transition that drives the AnimatedContent that performs the navigation transition.

• You should create a Transition based on the provided args and backStackDepth to track the current state.

• The created Transition will be used by AnimatedNavDecoration to display the correct content.

Implement Decoration

• This is a composable that renders the content for the target navigation destination.

• It receives the created targetState and an innerContent composable to render the actual screen's content.

• It will be used to compose the ui in the AnimatedContent.

Example

data class CustomNavState<T : NavArgument>(
  val args: ImmutableList<T>,
  override val backStackDepth: Int,
  override val screen: Screen = args.first().screen,
  override val rootScreen: Screen = args.last().screen,
) : AnimatedNavState

class CustomDecorator<T : NavArgument>() : AnimatedNavDecorator<T, CustomNavState<T>> {

  override fun AnimatedContentTransitionScope<AnimatedNavState>.transitionSpec(
    animatedNavEvent: AnimatedNavEvent
  ): ContentTransform {
    return slideInVertically() + fadeIn() togetherWith slideOutVertically() + fadeOut()
  }

  override fun targetState(args: ImmutableList<T>, backStackDepth: Int): CustomNavState<T> {
    // Logic to build your custom navigation state
    return CustomNavState(args, backStackDepth)
  }

  @Composable
  override fun updateTransition(
    args: ImmutableList<T>,
    backStackDepth: Int,
  ): Transition<CustomNavState<T>> {
    val targetState = targetState(args, backStackDepth)
    return updateTransition(targetState = targetState, label = "CustomDecoratorTransition")
  }

  @Composable
  override fun AnimatedContentScope.Decoration(
    targetState: CustomNavState<T>,
    innerContent: @Composable (T) -> Unit,
  ) {
    Box(modifier = Modifier.fillMaxSize()) { innerContent(targetState.args.first()) }
  }
}

Parameters

See also

Inheritors