Crossfade

@Composable
fun <T : Any?> Crossfade(
    targetState: T,
    modifier: Modifier = Modifier,
    animationSpec: FiniteAnimationSpec<Float> = tween(),
    label: String = "Crossfade",
    content: @Composable (T) -> Unit
): Unit

Crossfade allows to switch between two layouts with a crossfade animation.

import androidx.compose.animation.Crossfade
import androidx.compose.material.Text

Crossfade(targetState = "A") { screen ->
    when (screen) {
        "A" -> Text("Page A")
        "B" -> Text("Page B")
    }
}

@ExperimentalAnimationApi
@Composable
fun <T : Any?> Transition<T>.Crossfade(
    modifier: Modifier = Modifier,
    animationSpec: FiniteAnimationSpec<Float> = tween(),
    contentKey: (targetState) -> Any? = { it },
    content: @Composable (targetState) -> Unit
): Unit

Crossfade allows to switch between two layouts with a crossfade animation. The target state of this Crossfade will be the target state of the given Transition object. In other words, when the Transition changes target, the Crossfade will fade in the target content while fading out the current content.

content is a mapping between the state and the composable function for the content of that state. During the crossfade, content lambda will be invoked multiple times with different state parameter such that content associated with different states will be fading in/out at the same time.

contentKey will be used to perform equality check for different states. For example, when two states resolve to the same content key, there will be no animation for that state change. By default, contentKey is the same as the state object. contentKey can be particularly useful if target state object gets recreated across save & restore while a more persistent key is needed to properly restore the internal states of the content.