Because of how the display list works with ActionScript 3, some methods of depth sorting will no longer work. One in particular is sorting objects on the screen based on their y location. In ActionScript 1 and 2, you could simply tell the clip to swapDepths at its _y location and be done with it. With AS3, this is no longer possible since no gaps can exist within the depths display list ("array").

An approach to obtaining the same functionality in AS3 is possible through an sorted array. Store the objects you want to arrange in an array. Then sort that array based on the y properties of the display objects within. All you have to do after that is place them in the display list in the order sorted. Ex:

ActionScript Code:

var sortedItems:Array = new Array(mc1, mc2, mc3);
function arrange():void {
sortedItems.sortOn("y", Array.NUMERIC);
var i:int = sortedItems.length;
while(i--){
if (getChildAt(i) != sortedItems[i]) {
setChildIndex(sortedItems[i], i);
}
}
}

Here the sortedItems array stores the display objects being sorted (mc1 - mc3). In the arrange function, that array is sorted based on their y properties and then added to the display list at their locations within the array (if not already there).

Though this is not quite as easy as swaping to the depth of the _y property, it still proves a fairly efficient means of sorting objects on the screen based on their y location.