3

I have a screen with an Image at one corner of the screen and I want to animate it to the centre of the screen. Something like going from

Icon(
    painter = //,
    contentDescription = //,
    modifier = Modifier.size(36.dp)
)

to

Icon(
    painter = //,
    contentDescription = //,
    modifier = Modifier.fillMaxSize()
)

The first one is placed at the top left corner of screen and the second one at the centre. How can I animate between the two states?

Arpit Shukla
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2 Answers2

7

To make animations work in Compose you need to animate a value of some particular modifier. There's no way how you can animate between different set of modifiers.

Following this documentation paragraph, you can animate value for Modifier.size.

First I wait for the size of the image to be determined, with this value the size modifier can be set (I use then with an empty Modifier before that) and then this value can be animated.

Here's a sample:

Column {
    val animatableSize = remember { Animatable(Size.Zero, Size.VectorConverter) }
    val (containerSize, setContainerSize) = remember { mutableStateOf<Size?>(null) }
    val (imageSize, setImageSize) = remember { mutableStateOf<Size?>(null) }
    val density = LocalDensity.current
    val scope = rememberCoroutineScope()
    Button(onClick = {
        scope.launch {
            if (imageSize == null || containerSize == null) return@launch
            val targetSize = if (animatableSize.value == imageSize) containerSize else imageSize
            animatableSize.animateTo(
                targetSize,
                animationSpec = tween(durationMillis = 1000)
            )
        }
    }) {
        Text("Animate")
    }
    Box(
        Modifier
            .padding(20.dp)
            .size(300.dp)
            .background(Color.LightGray)
            .onSizeChanged { size ->
                setContainerSize(size.toSize())
            }
    ) {
        Image(
            Icons.Default.Person,
            contentDescription = null,
            modifier = Modifier
                .then(
                    if (animatableSize.value != Size.Zero) {
                        animatableSize.value.run {
                            Modifier.size(
                                width = with(density) { width.toDp() },
                                height = with(density) { height.toDp() },
                            )
                        }
                    } else {
                        Modifier
                    }
                )
                .onSizeChanged { intSize ->
                    if (imageSize != null) return@onSizeChanged
                    val size = intSize.toSize()
                    setImageSize(size)
                    scope.launch {
                        animatableSize.snapTo(size)
                    }
                }
        )
    }
}

Result:

Phil Dukhov
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6

Try this one out:

@Composable
fun DUM_E_MARK_II(triggered: Boolean) {
    BoxWithConstraints {
        val size by animateDpAsState(if (triggered) 36.dp else maxHeight)
        Icon(
            imageVector = Icons.Filled.Warning,
            contentDescription = "Just a better solution to the problem",
            modifier = Modifier.size(size)
        )
    }
}
Richard Onslow Roper
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  • The gif is a bit laggy, but that is error in recording. The actual animation is pretty smooth. – Richard Onslow Roper Oct 29 '21 at 12:04
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    So, what makes you think that this is not the correct solution? It is more effective compared to the marked answer. – Richard Onslow Roper Oct 30 '21 at 17:56
  • This is the easier solution. Thanks! – Tgo1014 Nov 25 '21 at 09:05
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    Just in case anyone needs the maximum height of the screen for that `maxHeight` parameter, you can get it by calling `LocalConfiguration.current.screenHeightDp` within a Composition Scope, thought it might help. –  Feb 23 '22 at 08:23