Android中創建Message兩種方法比較，new Message和obtainMessage

儘管Message的構造器是公開的，但是獲取Message對象的最好方法是調用Message.obtain()或者Handler.obtainMessage(), 這樣是從一個可回收對象池中獲取Message對象。

讓我們來看一下Message中obtain的源碼：

/**
     * 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();
    }

從全局message pool中獲取一個，比重新分配內存更有效！！

Handler.obtainMessage()方法的使用！

 /**
     * Returns a new {@link android.os.Message Message} from the global message pool. 
　　　* More efficient than creating and allocating new instances. 
　　  * The retrieved message has its handler set to this instance 　　　
　　　* (Message.target == this).
     * If you don't want that facility, just call Message.obtain() instead.
     */
   

    public final Message obtainMessage()
    {
        return Message.obtain(this);
    }

從以上方法可以看出，儘量不要new message兒是從全局message池中obtain會提升性能