Qt multithreading and let the second thread update the main (UI) thread

[anda_skoa]

Thanks for clarifying. I will usually register my custom types whether or not I am using threads and cross-thread signals/slots. I believe the other beneficial reason to do so is that you can use QVariant for custom types that have been registered, which may come in handy too.

Right, Q_DECLARE_METATYPE is required for encapsulating the type in QVariant. qRegisterMetaType() is needed, if the QVariant needs to be created without calling fromValue().
Which is the case of a signal/slot connection using Qt::QueuedConnection (such as a cross-thread one).

Cheers,
_