转自：http://iaiai.iteye.com/blog/1992196

obtainmessage（）是从消息池中拿来一个msg 不需要另开辟空间new
new需要重新申请，效率低，obtianmessage可以循环利用；

//use Handler.obtainMessage(),instead of msg = new Message();

//because if there is already an Message object,that not be used by

//any one ,the system will hand use that object,so you don't have to

//create and object and allocate memory.

//it  is also another example of object recycling and reusing in android.

    Message msg = mHandler.obtainMessage();

    msg.what = UPDATE_LISTVIEW;

    msg.obj = current + "/" + total + "songs";

    //this method is called from worker Thread,so we cannot update UI from here.

    msg.sendToTarget();

在看下面代码：

Message msg = handler.obtainMessage();

                        msg.arg1 = i;

                        msg.sendToTarget();   

Message msg=new Message();

    msg.arg1=i;

    handler.sendMessage(msg);

第一种写法是message 从handler 类获取，从而可以直接向该handler 对象发送消息，第二种写法是直接调用 handler 的发送消息方法发送消息。