From This Day

Just a note here, if you would have to pass custom data types between threads in Qt. As we know, a signal-slot connection is then (by default) of type Qt::QueuedConnection. Because in such a situation Qt needs to store passed parameters for a while, it creates their temporary copies. If it doesn’t recognize the passed data type, throws out an error:

QObject::connect: Cannot queue arguments of type 'MyType'

So custom data types have to be registered using qRegisterMetaType(), like in the example:

qRegisterMetaType<MyType>( "MyType" );

And this example is literal ⇒ when your class is called MyType, you register it as "MyType". Lastly I did something similar to this:

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typedef QMap<QString,QImage> MapStringImage;
(...)
qRegisterMetaType<MapStringImage>( "images" );

I didn’t get the error from QObject::connect (!), but also didn’t get things working. Wasted few hours hacking QMetaType class with no effect, and then more by accident than design changed "images" to "MapStringImage" and woo-hoo! That was my only problem… That’s why I’m stressing this naming issue, especially that documentation doesn’t tell a lot about it.

BTW I needed to use typedef because otherwise Qt didn’t have a clue what to do with such a complex type.