transition_animated_fab.kt

@Composable
private fun FabContainer(
  modifier: Modifier = Modifier,
) {
  var containerState by remember { mutableStateOf(ContainerState.Fab) }
  val transition = updateTransition(targetState = containerState)
  val backgroundColor by transition.animateColor { state ->
    when (state) {
      ContainerState.Fab -> Colors.fabContainerColor
      ContainerState.Fullscreen -> Colors.surface
    }
  }
  val cornerRadius by transition.animateDp { state ->
    when (state) {
      ContainerState.Fab -> 22.dp
      ContainerState.Fullscreen -> 0.dp
    }
  }
  val elevation by transition.animateDp { ... }
  val padding by transition.animateDp { ... }

  transition.AnimatedContent(
    modifier = modifier
      // padding, shadow, and backgroundColor are shared between composables
      .padding(end = padding, bottom = padding)
      .shadow(
        elevation = elevation,
        shape = RoundedCornerShape(cornerRadius)
      )
      .drawBehind { drawRect(backgroundColor) }
  ) { state ->
    when (state) {
      ContainerState.Fab -> Fab()
      ContainerState.Fullscreen -> AddContentScreen()
    }
  }
}