Issue of using moc on a custom type in a library

tzma

Basically, I created a library containing a type:

struct MyCustomType
{
...
};
Q_DECLARE_METATYPE(MyCustomType);

Then in my application, I have a signal "void sendMsg(MyCustomType)" and I qRegisterMetaType<MessageTableData>().

The code compiles and runs ok. But when I try to emit the signal, I got this error:
QObject::connect: Cannot queue arguments of type 'MyCustomType'
(Make sure 'MyCustomType' is registered using qRegisterMetaType().)

I did some research. I think for Qt5, a custom type, moc should have a section to automatically register the type like:
void MyApp::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
{
...
else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
... reinterpret_cast<int>(_a[0]) = qRegisterMetaType< MyCustomType >();
}

But I am missing this section in my moc generated file. Is this a known issue for a type in lib and any solution to this? Thanks!

Christian Ehrlicher

Is your type in a namespace?

tzma

No it's not in a namespace. Better be?

TheoSys

I've done this like:

class MainWindow : public QMainWindow
{
    Q_OBJECT

    public:
        MainWindow();
        ~MainWindow();

    signals:
        void sigYourSignal(size_t size, QByteArray ba);
}

int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow mainWin;
    mainWin.show();
    return app.exec();
}

MainWindow::MainWindow()
{
    qRegisterMetaType<size_t>("size_t");
    qRegisterMetaType<QByteArray>("QByteArray");
}

Then you can use this types with your signals as normal parameters.

A.T.

Christian Ehrlicher

@tzma said in Issue of using moc on a custom type in a library:

Better be?

No but this could have been a reason.
Are you sure you really call qRegisterMetaType somehwere before you use it in a signal?

tzma

Hi A.T. Do you mean to treat the custom type as a QByteArray? And what's the purpose of size since QByteArray has size()/length() already?

tzma

@Christian-Ehrlicher Yes. I have a valid ID returned from qRegisterMetaType call.

Christian Ehrlicher

I would suggest that you create a simple main.cpp with a queued connection of your type to see if it occours there too. This has also the advantage that we can try to reproduce it.

tzma

Thanks for the suggestion. I simplified the code quite a bit and the problem went away.