Flash AS3 Multi touch event handler - actionscript-3

Question

I have 3 separate movie clips in a frame, each clip can be moved around the stage using a simple touch and drag event, which is shown below, incase it has some relevance. I want to drag each of the three clips onto a fourth clip and when all 3 are contained within the fourth clip I want an event triggered that changes the current frame. What is the easiest way of doing this in AS3 ? Any examples would be great as I am a complete beginner. Thanks
Multitouch.inputMode = MultitouchInputMode.TOUCH_POINT;
Gem1_MC.addEventListener(TouchEvent.TOUCH_BEGIN, fl_TouchBeginHandler_2);
Gem1_MC.addEventListener(TouchEvent.TOUCH_END, fl_TouchEndHandler_2);
var fl_DragBounds_2:Rectangle = new Rectangle(0, 0, stage.stageWidth, stage.stageHeight);
function fl_TouchBeginHandler_2(event:TouchEvent):void
{
event.target.startTouchDrag(event.touchPointID, false, fl_DragBounds_2);
}
function fl_TouchEndHandler_2(event:TouchEvent):void
{
event.target.stopTouchDrag(event.touchPointID);
}

Answer 1

In the future you'd want to implement a solution where your drag and drop functionality is abstracted into a class but to work with what you've got, here's a basic solution:
Keep track of when the three MovieClips are considered "contained within" the fourth clip
var contained:Array = new Array(false, false, false);
In the event of an object finishing it's drag, check to see if it's contained in mc1. At the end of these checks, find out if they're all true:
function fl_TouchEndHandler_2(event:TouchEvent):void {
// Drag & drop stuff...
contained[2] = Gem2_MC.hitTestObject(Gem4_MC)); // where Gem4_MC is your 4th movie clip.
if (contained.indexOf(false) == -1) { // This returns -1 if it can't find false
gotoAndStop(frame_number_you_want);
}
}
As a side note, hitTestObject() uses a simple "bounding box" to dectect "collision". This means it may register a hit as true even when two movie clips don't look like they're actually touching. Pixel perfect collision detection in Flash is possible but more complicated and worth its own post. A simple example of pixel perfect collision in AS3 can be found here.