actionscript 3 - Flex 3: Determine if scroll panel child is visible -

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let's have canvas fixed height , vertical scroll bar. , canvas has 10 children in vertical line (like vbox) combined height exceeds height of canvas. based on scroll bar position, of children visible @ time.

is possible determine children visible? or whether or not specific child visible on screen?

i’m not sure on timeliness of answer, had similar question , following code worked me:

if (item.y < container.verticalscrollposition || item.y + item.height - container.verticalscrollposition > container.height) {       // item not (completely) visible  }

basically checking against following criteria:

1) item’s y position above container’s current vertical scroll position (i.e. outside of container’s top boundary)?

2) item’s bottom position scrolled outside of container’s bottom boundary? calculated using item’s bottom position (i.e. item’s y position plus height) minus current vertical scroll position.

if want check of items in container, you’d have loop through , check each against these criteria. throw above code in function , return whether item visible or not. there might better/cleaner way, haven’t found 1 yet.


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