how can i inherit from both QWidget and QThread?

Question

I have a class like this
class GUI : public QWidget, public QThread

When I do the above i get errors about connect signals. The error says "Reference to "connect" is ambiguous". Is there a way to inherit from both?

Thank you

Answer 1

You can't. Both QWidget and QThread inherit (non-virtually) from QObject. You therefore do not have virtual derivation, thus two copies of QObject, which confuses the compiler. QObject was specifically designed this way. See:

• http://lists.trolltech.com/qt-interest/2006-10/msg00711.html
• http://www.qtforum.org/article/23295/problem-opening-the-qfiledialog.html

There are some who allegedly went around this (can't find the link right now, but it's out there on Google, I had the same trouble two weeks ago), but it is unsafe at best.

Edit: the best way would probably be to have another object inherit from QThread and keep that object as a member in your GUI class. That is the sort of workaround most people do in this matter.

Answer 2

You cannot inherit from multiple QObjects.

You can inherit from one and make the other a member variable and work from there.

class GUI : public QWidget 
{
  QThread myThread;
};

You've named your class GUI - is this the main GUI of your program? See the examples in the Qt examples folder - they have sample programs on both GUI's and Threads.