怎样使MC倒放

on (release) 
{
        _root.onEnterFrame = function()
        {
                if(this.mc._currentframe == 1)
                {
                        delete this.onEnterFrame;
                }
                this.mc.prevFrame();
        }
}

a_btn.onRelease = function() {
delete this._parent.mc.onEnterFrame;
this._parent.mc.play();
};
b_btn.onRelease = function() {
this._parent.mc.stop();
this._parent.mc.onEnterFrame = function() {
  this.prevFrame();
};
};