Message创建方式：new Message和obtainMessage的区别

1. 前言

创建Message对象的时候，有三种方式，分别为： 
1.Message msg = new Message(); 
2.Message msg2 = Message.obtain(); 
3.Message msg1 = handler1.obtainMessage(); 
这三种方式有什么区别呢？

2.使用方式

public class MainActivity extends Activity {    private Handler handler1 = new Handler() {        @Override        public void handleMessage(Message msg) {            Toast.makeText(MainActivity.this, "hanlder1", Toast.LENGTH_SHORT).show();            super.handleMessage(msg);        }    };    ;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        new Thread(new Runnable() {            @Override            public void run() {//                Message msg = new Message();//                Message msg2 = Message.obtain();                Message msg1 = handler1.obtainMessage();                msg1.arg1 = 1;                handler1.sendMessage(msg1);            }        }).start();    }}
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3.源码讲解

1）Message msg = new Message();这种就是直接初始化一个Message对象，没有什么特别的。 
2）Message msg2 = Message.obtain();

/**     * Return a new Message instance from the global pool. Allows us to     * avoid allocating new objects in many cases.     */    public static Message obtain() {        synchronized (sPoolSync) {            if (sPool != null) {                Message m = sPool;                sPool = m.next;                m.next = null;                m.flags = 0; // clear in-use flag                sPoolSize--;                return m;            }        }        return new Message();    }
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从注释可以得知，从整个Messge池中返回一个新的Message实例，通过obtainMessage能避免重复Message创建对象。 
3）Message msg1 = handler1.obtainMessage();

public final Message obtainMessage()    {        return Message.obtain(this);    }
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public static Message obtain(Handler h) {        Message m = obtain();        m.target = h;        return m;    }
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public static Message obtain() {        synchronized (sPoolSync) {            if (sPool != null) {                Message m = sPool;                sPool = m.next;                m.next = null;                m.flags = 0; // clear in-use flag                sPoolSize--;                return m;            }        }        return new Message();    }
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可以看到，第二种跟第三种其实是一样的，都可以避免重复创建Message对象，所以建议用第二种或者第三种任何一个创建Message对象。