shuru_txt.addEventListener(MouseEvent.CLICK, shurujianting1 );
function shurujianting1(event: MouseEvent):void
{
shuru_txt.restrict = "0-9";

}

//文本框只能输入数字的代码，其他字符无效。

如果要输入小数点：

shuru_txt.restrict = "0-9\.";