Android Looper和Handler分析(12)

//待会看dispatchMessage的时候再分析  
public Handler(Looper looper, Callback callback) { 
        mLooper = looper; 
        mQueue = looper.mQueue; 
        mCallback = callback; 
    } 
//  
//通过handler发送消息  
//调用了内部的一个sendMessageDelayed  
public final boolean sendMessage(Message msg) 
    { 
        return sendMessageDelayed(msg, 0); 
    } 
//FT，又封装了一层，这回是调用sendMessageAtTime了  
//因为延时时间是基于当前调用时间的，所以需要获得绝对时间传递给sendMessageAtTime  
public final boolean sendMessageDelayed(Message msg, long delayMillis) 
    { 
        if (delayMillis < 0) { 
            delayMillis = 0; 
        } 
        return sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis); 
    } 
 
 
public boolean sendMessageAtTime(Message msg, long uptimeMillis) 
    { 
        boolean sent = false; 
        MessageQueue queue = mQueue; 
        if (queue != null) { 
//把消息的target设置为自己，然后加入到消息队列中  
//对于队列这种数据结构来说，操作比较简单了  
            msg.target = this; 
            sent = queue.enqueueMessage(msg, uptimeMillis); 
        } 
        else { 
            RuntimeException e = new RuntimeException( 
                this + " sendMessageAtTime() called with no mQueue"); 
            Log.w("Looper", e.getMessage(), e); 
        } 
        return sent; 
    } 
//还记得looper中的那个消息循环处理吗  
//从消息队列中得到一个消息后，会调用它的target的dispatchMesage函数  
//message的target已经设置为handler了，所以  
//最后会转到handler的msg处理上来