Handler sendMessage 与 obtainMessage (sendToTarget)比较

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；

1. //use Handler.obtainMessage(),instead of msg = new Message();
2. //because if there is already an Message object,that not be used by
3. //any one ,the system will hand use that object,so you don't have to
4. //create and object and allocate memory.
5. //it  is also another example of object recycling and reusing in android.
6. Message msg = mHandler.obtainMessage();
7. msg.what = UPDATE_LISTVIEW;
8. msg.obj = current + "/" + total + "songs";
9. //this method is called from worker Thread,so we cannot update UI from here.
10. msg.sendToTarget();

//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：

1. Message msg = handler.obtainMessage();
2. msg.arg1 = i;
3. msg.sendToTarget();
4. Message msg=new Message();
5. msg.arg1=i;
6. handler.sendMessage(msg);

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。