Q_DECLARE_METATYPE and qRegisterMetaType?

EStudley

Hello all,

I am using Qt 5.4.2. I have an enum, ClientError, that I am trying to use in several ways:

A meta type for use with QVariants in a QAbstractListModel:

 errorVariant.canConvert<ErrorHandler::ClientError>()

A function parameter:

ErrorModel::addError(ErrorHandler::ClientError)

A QML enum:

errorModel.addError(ClientError.MajorError)

ErrorHandler.h contains the following:

class ErrorHandler : public QObject
{
    Q_OBJECT
    Q_ENUMS(ClientError)
public:
    enum ClientError
    {
        MajorError,
...
...
};

Q_DECLARE_METATYPE(ErrorHandler::ClientError)

#endif // ERRORHANDLER_H

Main.cpp contains the following:

#include <client/ErrorHandler.h>

int main(int argc, char **argv)
{
...
...
    qRegisterMetaType<ErrorHandler::ClientError>("ErrorHandler::ClientError");
    qmlRegisterUncreatableType<ErrorHandler>("Client", 1, 0, "ClientError","Display Client Errors");

When I build, I get the following:

main.obj:-1: error: LNK2019: unresolved external symbol "public: static struct QMetaObject const ErrorHandler::staticMetaObject" (?staticMetaObject@ErrorHandler@@2UQMetaObject@@B) referenced in function "int __cdecl qRegisterNormalizedMetaType<class ErrorHandler *>(class QByteArray const &,class ErrorHandler * *,enum QtPrivate::MetaTypeDefinedHelper<class ErrorHandler *,1>::DefinedType)" (??$qRegisterNormalizedMetaType@PEAVErrorHandler@@@@YAHAEBVQByteArray@@PEAPEAVErrorHandler@@W4DefinedType@?$MetaTypeDefinedHelper@PEAVErrorHandler@@$00@QtPrivate@@@Z)

Am I doing anything wrong? Is it possible to double-use an enum in this way?

Thanks.

VRonin

Q_ENUMS is deprecated, use Q_ENUM that already includes the Q_DECLARE_METATYPE so no need to explicitly add it. Also you don't need to register QObject derived types

EStudley

I'm currently using Qt 5.4.2; it seems like that's a newer feature.

kshegunov

Is this a library? I mean where you define the ErrorHandler class. If so you need to export that class from it.

PS. Also use qRegisterMetaType without a string argument:

qRegisterMetaType<ErrorHandler::ClientError>();

EStudley

By export you mean "CONFIG += client" in clientApp.pro, correct?

I tried without a string argument, same result.

kshegunov

Not at all, unless your library is a module QT += is not going to work and CONFIG += is for qmake features/configurations so it has no place here. I mean like described here.

EStudley

It is a library and it's exported correctly. I am able to access a different enum from a different class in the same library from QML; the only difference is me using Q_DECLARE_METATYPE with ClientError.

kshegunov

@EStudley said in Q_DECLARE_METATYPE and qRegisterMetaType?:
Firstly, you shouldn't need to use Q_DECLARE_METATYPE (or qRegisterMetaType) with the enum at all, this is handled by the moc. Here you can see that the macro expands to nothing.
Secondly, your linker (MSVC) complains that it can't find the metaObject for your ErrorHandler enum, which is normal as it is not exported from the binary by Q_DECLARE_METATYPE.

In conclusion:
Don't use Q_DECLARE_METATYPE and qRegisterMetaType for your QObject enum. Use it if you want to use it as a global enumerator and then you need to call the meta-type runtime registration from the library, not from the application.

EStudley

Thanks! That seemed to solve my issues.