Crash when closing application

[Joel Bodenmann]

@kshegunov said:

And by the way you don't need the destructors in your interfaces. They will generate object code (because virtual methods can't be inlined) and you don't really need to enforce them virtual, as QObject already does that.

The reason I added those virtual destructors there is because Qt documenation adviced me to do so: https://doc.qt.io/qt-4.8/qt-tools-plugandpaint-example.html

The class also has a virtual destructor. Interface classes usually don't need such a destructor (because it would make little sense to delete the object that implements the interface through a pointer to the interface), but some compilers emit a warning for classes that declare virtual functions but no virtual destructor. We provide the destructor to keep these compilers happy.

[kshegunov]

@Joel-Bodenmann

The reason I added those virtual destructors there is because Qt documenation adviced me to do so

Right, it's not an error by any means. However, I advise not using substandard compilers instead. ;)