Correct way to register with QMetaType

CJha

How should I register my class/struct that is inside a namespace:

namespace base {
    namespace impl {
        class A
        {
            ...
        };
    }
}
Q_DECLARE_METATYPE(base::impl::A);

I want to use this class inside base::impl namespace as well as base::util namespace.
How would I register this with qRegisterMetaType:

qRegisterMetaType<base::impl::A>("base::impl::A");
// or
qRegisterMetaType<base::impl::A>("A");
// or
qRegisterMetaType<base::impl::A>();

How would I register this with qRegisterMetaTypeStreamOperators:

qRegisterMetaTypeStreamOperators<base::impl::A>("base::impl::A");
// or
qRegisterMetaTypeStreamOperators<base::impl::A>("A");
// or
qRegisterMetaTypeStreamOperators<base::impl::A>();

Also, I will be using this class in different ways, like QVector<QVector<base::impl::A>>, std::shared_ptr<base::impl::A> and QVector<QVector<std::shared_ptr<base::impl::A>>> should I register these as well with qRegisterMetaType and qRegisterMetaTypeStreamOperators or just registering the class itself (i.e. base::util::A) will be enough? If I should then what will be the signature?

SGaist

Hi,

How exactly are you using your class ?
Because just using it in a different namespace does not require to register it. Are you using it with QVariant ?

CJha

@SGaist Yes, I am using it with QVariant, mostly with QSettings to save and retrieve data easily by overriding QDataStream operators. I am also using some in queued signal and slot connections. The ones I am registering for are mostly structs for storing data and just a few simple classes.

Due to these requirements, I need to use all three (Q_DECLARE_METATYPE, qRegisterMetaType and qRegisterMetaTypeStreamOperators) operators, but to me, it seems to work fine if I do not add the string part at all, i.e. register as:

qRegisterMetaType<base::impl::A>();  // or
qRegisterMetaType<QVector<base::impl::A>>(); // or
qRegisterMetaTypeStreamOperators<base::impl::A>(); // or
qRegisterMetaTypeStreamOperators<QVector<base::impl::A>>();
...

But, it also works fine if I add the string part inside the brackets:

qRegisterMetaType<base::impl::A>("base::impl::A");  // or
qRegisterMetaType<QVector<base::impl::A>>("QVector<base::impl::A>"); // or
qRegisterMetaTypeStreamOperators<base::impl::A>("base::impl::A"); // or
qRegisterMetaTypeStreamOperators<QVector<base::impl::A>>("QVector<base::impl::A");
...

The definition as well as most of the examples I see does provide a string part inside the brackets (especially for qRegisterMetaTypeStreamOperators). Which makes me confused as to what is the reason behind adding the string part such as "base::impl::A" inside the brackets and how does it affect the usage?

Debugging problems caused by these kinds of ambiguity (especially on VS) is difficult and I do not want to make mistakes now which might give me errors later and would consume a lot of my time in figuring out that I registered the type or stream operators incorrectly.

SGaist

If memory serves well, the version with a QString parameter is geared toward declaring aliases.