CrossfadeRetain.kt

package com.example.lifelike

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.compose.Composable
import androidx.compose.onActive
import androidx.compose.state
import androidx.ui.animation.Crossfade
import androidx.ui.core.setContent
import androidx.ui.foundation.Clickable
import androidx.ui.foundation.ColoredRect
import androidx.ui.graphics.Color
import androidx.ui.layout.LayoutHeight
import androidx.ui.layout.LayoutWidth
import com.example.lifelike.MainActivity.Route.*

class MainActivity : AppCompatActivity() {

    enum class Route {
        Red, Black
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            var route by state { Black }
            Crossfade(current = route) {
                Test(it) {
                    route = when (route) {
                        Red -> Black
                        Black -> Red
                    }
                }
            }
        }
    }

    @Composable
    fun Test(route: Route, onSwitch: () -> Unit) {
        onActive {
            println("${route.name}: active")
            onDispose {
                println("${route.name}: dispose")
            }
        }

        val color = when (route) {
            Red -> Color.Red
            Black -> Color.Black
        }
        Clickable(onSwitch) {
            ColoredRect(color = color, modifier = LayoutWidth.Fill + LayoutHeight.Fill)
        }
    }
}