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Source code

void SomeClass::handler(QEvent* event)
{
  // do stuff
  event->accept();
}

void SomeClass::handler(QEvent* event)
{
  // do stuff
  Base::handler(event); // SomeClass is derived from Base.
}

Source code

// use this very simple way if you dont need to pass the event around
// `event` here is qt event - no need to subclass
class::eventhandler(event)
{
  if event is LMB
  // do stuff, pretending RMB
  elif event is RMB 
  // do stuff, pretendending LMB

  // throw away event, do not pass to base class
}

Source code

// if you DO need to pass the event around
// `eventSubclass` here is your own subclass, inheriting the Qt event class (don't even know if this is well supported) 
class::eventhandler(eventSubclass)
{
  if eventSubclass is LMB
  // do stuff for LMB - eventSubclass switches the buttons
  elif eventSubclass is RMB 
  // do stuff for RMB

  //if you need to pass event deeper, then it obviously has 
  //to be wrapped if you want to keep pretending the buttons are switched
    Base::eventhandler(eventSubclass); 

  // A bizarre alternative is where you want to pass the event with 'normal' buttons
  // into event handler, in which case use above example - no need for event wrapper here.
}