While learning Actionscript 3, my button rollovers were not working correctly. The problem was that I didn’t know the difference between target and currentTarget or between MOUSE_OVER and ROLL_OVER. I made an example to demonstrate and I hope to explain it in a way that will save you some time.
AS3 Mouse events use two different properties: target and currentTarget. “target” is the object that fired the MOUSE_OVER (or MOUSE_OUT) event. “currentTarget” is the Movieclip that you applied the listener to. In the example below, the top 2 buttons have MOUSE_OVER and MOUSE_OUT listeners. Each button is made up of 6 different MovieClips. As you rollover the button on the left, the target fades. As you rollover the button on the right, the currentTarget fades. So, you want to use currentTarget right?
WRONG! Watch the output text window at the bottom of the Flash movie as you rollover the button on the right. Even though it appears to be highlighting correctly, it is actually firing a MOUSE_OVER event for every movieclip inside the button! This is not what you want! You want the event to fire once – when you rollover the button. This is where mouseChildren comes in! In the second row of buttons, I have set the mouseChildren property of both buttons to false. This means that none of the internal movieclips will fire an event. Now, when you rollover the buttons, you can see that they highlight correctly and that the target and currentTarget values are the same.
But there is an easier way – use ROLL_OVER and ROLL_OUT! These events automatically ignore the the internal structure of the buttons and register events only on the object that the listener was assigned to (in this case, the button itself). Most of the time, these are the events you will want to use. I rarely use MOUSE_OVER or MOUSE_OUT for anything.
I hope this example helps to clear up some confusion. You can download the source files here and play around with them.