Why does touch event take place in lower layer not top layer of the screen ?:Need help!

I added touchable objects before I added the floor.
I found that I can touch objects which are behind the floor. I want objects cannot be touch behind the floor.
After test, I found that object which was first added in displayGroup was the first object that got touch event. I do not know how to solve this problem. Just want the touch event only takes place on top layer of the screen.

views:1308 update:2011/10/19 14:58:09
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