Problems with Open-Source Downloads read https://www.qt.io/blog/problem-with-open-source-downloads and https://forum.qt.io/post/638946

"New" signal slot syntax with signals defined in abstract base class requires horrible cast?



  • Hi.
    I thought I'd eliminate the SIGNAL/SLOT macros from my code until I found out that I needed to do horrible casts like this:

    connect(app_->data_manager(), static_cast<void (DataManager::*)(const Data&)>(&DataManager::CurrentDataChanged), &DataBase::CurrentDataChanged);
    

    because the signal CurrentDataChanged is defined in the abstract base class of DataManager.

    Is this really the correct way to do this with the new syntax? Once I realized this, I just quickly reverted to the SIGNAL/SLOT macros, because the new syntax just seems too much of a hassle.



  • @Diracsbracket
    Well, that depends on exactly how you have defined the signatures of the signal and the slot. Qt has plenty of signals/slots defined in its abstract base classes without requiring the casting you show.

    It's up to you, but personally at least I still miles prefer new style with edit- and compile-time help, as opposed to the old macros which if you get wrong you only find out at runtime. You can always typedef the signatures out of the classes to use elsewhere, so that even if that code is needed you don't have to write it every time.


  • Moderators

    @Diracsbracket said in "New" signal slot syntax with signals defined in abstract base class requires horrible cast?:

    because the signal CurrentDataChanged is defined in the abstract base class of DataManager.

    That doesn't sound like a reason for casting.

    • What error message do you get without the cast?
    • Is CurrentDataChanged overloaded or overridden?

    As @JonB mentioned, the signals of QAbstractItemView (https://doc.qt.io/qt-5/qabstractitemview.html#signals ) don't require casting, for example.


Log in to reply