title: qt inherited signal won't reach to slot
body: <p>here's the code of my problem  </p>
  
  <pre><code>class Base : QThread  
  {
     Q_OBJECT  
   virtual void run() = 0;  
  signals:  
   void Ping(int);  
  };  
  
  class Derived : public Base  
  {  
    void run()  
    {  
      emit Ping(42);  
    }  
  }  
  </code></pre>
  
  <p>the signal(42) won't reach/call to slots. what's wrong?
  thanks in advance.</p>