Message

获取消息

• Message.obtain();
  从消息池获取消息

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();
    } 

• mHandle.obtainMessage();
  或Message.obtain(mHandle, what);
  或Message.obtain(mHandle, what, obj);
  或Message.obtain(mHandle, what, arg1, arg2);
  等等......

public static Message obtain(Handler h) {
    Message m = obtain();
    m.target = h;
    return m;
}

注意：这个不能mHandle.sendMessage(msg);而应该msg.sendToTarget();
1,Message设置数据

 Bundle data = new Bundle();
 data.putString(key, value);
 data.putStringArray(key, value);
 msg.setData(data);  

2,handleMessage(Message msg)获取数据

Bundle data = msg.getData();  

• Message.obtain(mHandle);

Handle

方法

• 发送消息，到MessageQueue中
  post(Runnable)
postAtTime(Runnable, long)
postDelayed(Runnable, long)
sendEmptyMessage(int)
sendMessage(Message)
sendMessageAtTime(Message, long)
sendMessageDelayed(Message, long)
  等等......
  1，post和send两种类型，post传的是Runnable，底层是调用getPostMessage将Runnable转Message

private static Message getPostMessage(Runnable r) {
    Message m = Message.obtain();
    m.callback = r;
    return m;
} 

• 将所有的Callbacks和Messages全部清除

mHandler.removeCallbacksAndMessages(null);

• 清除指定what的Message

mHandler.removeMessages(what);

Looper

• 子线程默认没有开启消息循环，没有创建消息队列，需要prepare(),loop()。
  Looper.prepare():绑定一个Looper,底层会创建一个Looper，创建Looper的构造函数中又会创建一个消息队列，参见android消息机制.md
  注意：此方法在当前线程只能调用一个，因为一个线程只能有一个Looper，否则会抛throw new RuntimeException("Only one Looper may be created per thread");异常
  Looper.loop():执行消息循环，直到消息队列循环结束

class LooperThread extends Thread {
      public Handler mHandler;
      public void run() {
          Looper.prepare();
          mHandler = new Handler() {
              public void handleMessage(Message msg) {
                  // process incoming messages here
              }
          };
          Looper.loop();
      }
  }