http://yhc447.pixnet.net/blog/post/41740408-%e7%b6%b2%e8%b7%af%e8%b6%a3%e8%81%9e~%e6%b4%bb%e7%89%a1%e8%a0%a3%e7%9a%84%e6%b7%a8%e6%b0%b4%e8%83%bd%e5%8a%9b這篇也有講到