Q_DECLARE_METATYPE with using and same types

kkettinger

Hello,

i'm having issues with Q_DECLARE_METATYPE. My header file:

// ...
namespace Storage
{
namespace Types
{
using tCommandValue = int;
using tStateValue = int;
using tEventValue = QVariant;
}
}

They are registered with qRegisterMetaType:

qRegisterMetaType<Storage::Types::tCommandValue>();
qRegisterMetaType<Storage::Types::tEventValue>();
qRegisterMetaType<Storage::Types::tStateValue>();

The usage in signal/slots:

void addEvent(const IDs::Events id, const Types::tEventValue value);

Now when using no Q_DECLARE_METATYPE, i get this error:

QObject::connect: Cannot queue arguments of type 'Storage::Types::tStateValue'
(Make sure 'Storage::Types::tStateValue' is registered using qRegisterMetaType().)

When i add the types with Q_DECLARE_METATYPE in my header file, i get a compile error:

// ...
Q_DECLARE_METATYPE(Storage::Types::tCommandValue);
Q_DECLARE_METATYPE(Storage::Types::tEventValue);
Q_DECLARE_METATYPE(Storage::Types::tStateValue); // <--- Error: redefinition of 'QMetaTypeId<int>'

Maybe someone has an idea.
Thanks!

Best regards,
Kevin

kkettinger

Found a solution. For POD-types that are already registered Q_DECLARE_METATYPE is not needed.
qRegisterMetaType is still needed but needs an additional type name:

qRegisterMetaType<Storage::Types::tStateValue>("Storage::Types::tStateValue");
qRegisterMetaType<Storage::Types::tEventValue>("Storage::Types::tEventValue");
qRegisterMetaType<Storage::Types::tCommandValue>("Storage::Types::tCommandValue");

SGaist

Hi,

The "named" version is needed because you are not declaring a new type but in fact you are declaring an allias.