Android Looper和Handler分析(13)

//这里有个处理流程的问题  
public void dispatchMessage(Message msg) { 
//如果msg本身设置了callback，则直接交给这个callback处理了  
        if (msg.callback != null) { 
            handleCallback(msg); 
        } else { 
//如果该handler的callback有的话，则交给这个callback处理了---相当于集中处理  
          if (mCallback != null) { 
                if (mCallback.handleMessage(msg)) { 
                    return; 
                } 
           } 
//否则交给派生处理,基类默认处理是什么都不干  
            handleMessage(msg); 
        } 
    } 
.......... 
} 
Cpp代码
class Handler{ 
.......... 
//handler默认构造函数 
public Handler() { 
//这个if是干嘛用的暂时还不明白，涉及到java的深层次的内容了应该 
        if (FIND_POTENTIAL_LEAKS) { 
            final Class<? extends Handler> klass = getClass(); 
            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) && 
                    (klass.getModifiers() & Modifier.STATIC) == 0) { 
                Log.w(TAG, "The following Handler class should be static or leaks might occur: " + 
                    klass.getCanonicalName()); 
            } 
        } 
//获取本线程的looper对象 
//如果本线程还没有设置looper，这回抛异常 
        mLooper = Looper.myLooper(); 
        if (mLooper == null) { 
            throw new RuntimeException( 
                "Can't create handler inside thread that has not called Looper.prepare()");