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# compose

[Slackbot]

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[Md. Nazmun Sadat Khan]

My guess is that the local variables of the lambda passed to detectDragGestures are already fixed when first called, so position is always IntOffset.Zero. Explicitly using the value parameter of the state solves this:

@Composable
fun DraggableSample() {
    Box(
        modifier = Modifier
            .fillMaxSize()
    ) {
        val position = remember { mutableStateOf(IntOffset.Zero) }

        DraggableCircle(position = position, onPositionChanged = { position.value = it })
    }
}

@Composable
fun DraggableCircle(
    modifier: Modifier = Modifier,
    position: MutableState<IntOffset>,
    onPositionChanged: (position: IntOffset) -> Unit
) {
    Box(
        modifier = modifier
            .offset { position.value }
            .size(100.dp)
            .background(color = Color.Green, CircleShape)
            .pointerInput(Unit) {
                detectDragGestures { change, dragAmount ->
                    onPositionChanged(dragAmount.toIntOffset() + position.value)
                    change.consumeAllChanges()
                }
            }
    )
}

private fun Offset.toIntOffset() = IntOffset(x.roundToInt(), y.roundToInt())

I don't know if there's a more elegant solution to this, but this works.

[Albert Chang]

You have two choices, one is to change the position parameter to positionChange and add the change on the call site (onPositionChange = { position += it }), the other is to add var currentPosition by rememberUpdatedState(position) in DraggableCircle and use currentPosition in pointerInput. Passing MutableState as parameter is not a good idea I'm afraid.