qt inherited signal won't reach to slot

here's the code of my problem

class Base : QThread  
{
   Q_OB开发者_如何学CJECT  
 virtual void run() = 0;  
signals:  
 void Ping(int);  
};  

class Derived : public Base  
{  
  void run()  
  {  
    emit Ping(42);  
  }  
}  

the signal(42) won't reach/call to slots. what's wrong? thanks in advance.

Did that 100 times, it does work. Are you sure your base class is properly MOC'ed ? (i.e. defined in a file contained in HEADERS section of .pro) Also when connecting your signal, check the return status of QObject::connect (it's a boolean). A good practice is something like that

bool r=false;
r=QObject::connect(pObj1,SIGNAL(signalStuff()),pObj2,SLOT(gotStuff()));
Q_ASSERT(r);

As Liz noticed, if something went wrong in your connect, you can check the traces to know what happened.

I can also note :

• you don't have to redefine run in your base class, it's already defined by QThread
• Common pitfall with QThread: Base class and Derived class belong to the thread which created them, not in the newly created thread
• you don't connect your signal to any slot in your sample, so it won't trigger anything (I suppose it's done elsewhere)
• your class Derived lacks the final ;

EDIT:

Edited to take into account liz' interesting comment.

I came upon the same problem but managed to find solution. The problem in my case wasnt the inheritance (even tho i did emit from derived class).

The problem was the code calling emit signal was execute BEFORE the code connecting signal with slot. Therefor both signal was emitted and signal-slot connection worked fine, but the code in the slot wasnt executed because emit happened before connecting the slot to signal.

Maybe that helps someone in the future.

I think you are trying to connect signal and slot from different threads. Did you read this article?