state-hoisting-simple.kt

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            PlayingWithComposeTheme {
                FavoriteAppScreen()
            }
        }
    }

    @Composable
    fun FavoriteAppScreen() {
        var favorite by remember { mutableStateOf(false) }
        var color by remember { mutableStateOf(Color.Gray) }

        ConstraintLayout(Modifier.fillMaxSize()) {
            color = if (favorite) {
                Color.Red
            } else {
                Color.Gray
            }
            val (imageFavorite) = createRefs()
            FavoriteButton(modifier = Modifier.constrainAs(imageFavorite) {
                start.linkTo(parent.start)
                top.linkTo(parent.top)
                end.linkTo(parent.end)
                bottom.linkTo(parent.bottom)
            }, color = color, onFavoriteValueChanged = {
                favorite = true
                if (color == Color.Red) {
                    favorite = false
                }
            }, favorite = favorite)

        }
    }

    @Composable
    fun FavoriteButton(
        modifier: Modifier = Modifier,
        favorite: Boolean,
        onFavoriteValueChanged: (Boolean) -> Unit,
        color: Color
    ) {
        Image(Icons.Default.Favorite,
            contentDescription = null,
            colorFilter = ColorFilter.tint(color),
            modifier = modifier
                .size(200.dp)
                .clickable { onFavoriteValueChanged(favorite) }
        )
    }

}