Flash: prevent the user from draging one thumb of a HSlider

I'm using Flash HSlider component. I used a slider with several thumbs. I'd like to prevent the user from draging just the middle thumb, but can drag other thumbs. I don't know how to do it. Could any one can 开发者_如何学编程give me some tips?

Thanks.

Yuan

on creation complete for the slider do...

slider.getThumbAt(middleThumbIndex).enabled = false;