I'm trying to drag a shape on a `Canvas`. I use `Modifier.draggable`, but the handler does not have ...

# compose

[robnik]

I'm trying to drag a shape on a Canvas. I use Modifier.draggable, but the handler does not have access to the Canvas's width, to constrain the drag. How can I pass the Canvas's width to the drag handler? Example in thread...

[robnik]

Example:

val offset = remember { mutableStateOf(0f) }
val dragState = rememberDraggableState { dx ->
    offset.value = (offset.value + dx).coerceIn(0f, ???) // canvas width?
}
Canvas(Modifier.fillMaxWidth().height(40.dp)
        .draggable(orientation = Orientation.Horizontal,
                   state = dragState)) {
    // this.size.width is available here. How to pass to the drag handler?
    drawThing(offset)
}

[Se7eN]

You can use Modifier.onSizeChanged on the Canvas to get it's size:

val size by remember { mutableStateOf(0.dp) }
val dragState = rememberDraggableState { dx ->
    offset.value = (offset.value + dx).coerceIn(0f, size.width)
}
Canvas(modifier = Modifier
          ...
          .onSizeChanged { size = it }
          ...
)

[Adriano Celentano]

you could use pointerInput like here
https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:compose/[…]s/src/main/java/androidx/compose/animation/demos/FlingGame.kt

[robnik]

Great, thanks guys!