动态|文本框|自适应
//as层
showtxt.autoSize = true;
showtxt.text = "Hello!";
onEnterFrame = function () {
textbg._width = showtxt._width;
textbg._height = showtxt._height;
arrow_mc._y = textbg._height;
arrow_mc._x = showtxt._width/2-arrow_mc._width/2;
};
//showtxt动态文本名
//textbg文本背景
//arrow_mc背景框箭头
//