QObject::connect: Cannot queue arguments of type

micha_eleric

int id = qRegisterMetaType< QList<float> >();

is in both classes that use QList<float>, and still get the error

HaoTian

@micha_eleric No no, it's not necessary to register anything. because QList is automatically registered by Qt and basic types do not need to be registered either.

ChrisW67

@HaoTian Indeed, you are correct. This, for example, works:

#include <QCoreApplication>
#include <QObject>
#include <QList>
#include <QDebug>
#include <QTimer>

class Object: public QObject {
        Q_OBJECT
public:
        Object(QObject *p = nullptr): QObject(p) {
                QTimer::singleShot(
                                5000, this,
                                [this]() { emit send(QList<float> { 0, 1.2, 2.3, 3.4 } ); }
                );
        };
        ~Object() { }

public slots:
        void receive(QList<float> list) {
                qDebug() << list;
        }
signals:
        void send(QList<float> list);

};


int main(int argc, char **argv) {
        QCoreApplication app(argc, argv);

        Object *a = new Object(qApp);
        Object *b = new Object(qApp);
        QObject::connect(a, &Object::send, b, &Object::receive);

        return app.exec();
}

#include "main.moc"

So, @micha_eleric, what are you not telling us? Are there threads involved? Can you modify the example above to fail in the same way?

JonB

@micha_eleric
First you should get your code compiling and running correctly as per @ChrisW67. You will need to use the Q_OBJECT macro., and you should use connect() syntax shown, not SIGNAL/SLOT() macros.

But you may end up needing to reconsider your array/list arguments to the signal/slot. I assume you are signalling across threads. Qt will copy any arguments. If your array is "large" or if you intend to update the array in the slot (not just read from it) you may/will need to reconsider.

SGaist

@ChrisW67 said in QObject::connect: Cannot queue arguments of type:

@HaoTian Indeed, you are correct. This, for example, works:

#include <QCoreApplication>
#include <QObject>
#include <QList>
#include <QDebug>
#include <QTimer>

class Object: public QObject {
        Q_OBJECT
public:
        Object(QObject *p = nullptr): QObject(p) {
                QTimer::singleShot(
                                5000, this,
                                [this]() { emit send(QList<float> { 0, 1.2, 2.3, 3.4 } ); }
                );
        };
        ~Object() { }

public slots:
        void receive(QList<float> list) {
                qDebug() << list;
        }
signals:
        void send(QList<float> list);

};


int main(int argc, char **argv) {
        QCoreApplication app(argc, argv);

        Object *a = new Object(qApp);
        Object *b = new Object(qApp);
        QObject::connect(a, &Object::send, b, &Object::receive);

        return app.exec();
}

#include "main.moc"

So, @micha_eleric, what are you not telling us? Are there threads involved? Can you modify the example above to fail in the same way?

If I may just add something: use const references, this will avoid potentially expensive copies when possible.

micha_eleric

@HaoTian which is why I wonder why it gives this error when it runs

QObject::connect: Cannot queue arguments of type 'QList<float>'
(Make sure 'QList<float>' is registered using qRegisterMetaType().)

micha_eleric

@ChrisW67 it is with threads, and the only place I have seen

QObject::connect: Cannot queue arguments of type 'QList<float>'
(Make sure 'QList<float>' is registered using qRegisterMetaType().)

show while running

micha_eleric

@JonB said in QObject::connect: Cannot queue arguments of type:

@micha_eleric
First you should get your code compiling and running correctly as per @ChrisW67. You will need to use the Q_OBJECT macro., and you should use connect() syntax shown, not SIGNAL/SLOT() macros.

But you may end up needing to reconsider your array/list arguments to the signal/slot. I assume you are signalling across threads. Qt will copy any arguments. If your array is "large" or if you intend to update the array in the slot (not just read from it) you may/will need to reconsider.

it compiles and runs, but

QObject::connect: Cannot queue arguments of type 'QList<float>'
(Make sure 'QList<float>' is registered using qRegisterMetaType().)

shows on console while running

SGaist

@micha_eleric Which version of Qt are you running ?

micha_eleric

@SGaist said in QObject::connect: Cannot queue arguments of type:

@micha_eleric Which version of Qt are you running ?

been asked this before, and still no clue how to find out. All I can find is the version of the editor.

CPPUIX

@micha_eleric said in QObject::connect: Cannot queue arguments of type:

how to find out

Which version of Qt am I using? How do I find out?

micha_eleric

@Abderrahmene_Rayene said in QObject::connect: Cannot queue arguments of type:

@micha_eleric said in QObject::connect: Cannot queue arguments of type:

how to find out

Which version of Qt am I using? How do I find out?

instructions do not work for my version of QT Create, and once i did find preference->kit->kit, nothing was listed under auto-detected nor manual

JKSH

@micha_eleric said in QObject::connect: Cannot queue arguments of type:

once i did find preference->kit->kit, nothing was listed under auto-detected nor manual

That sounds very strange.

What do you see when you try Step #2 in the instructions?

micha_eleric

@JKSH said in QObject::connect: Cannot queue arguments of type:

@micha_eleric said in QObject::connect: Cannot queue arguments of type:

once i did find preference->kit->kit, nothing was listed under auto-detected nor manual

That sounds very strange.

What do you see when you try Step #2 in the instructions?

lol, second step also gave no version, but can find editor version elsewhere
Qt Creator 6.0.2
Based on Qt 5.15.3 (GCC 11.2.0, 64 bit)

Pl45m4

@micha_eleric said in QObject::connect: Cannot queue arguments of type:

Qt Creator 6.0.2
Based on Qt 5.15.3 (GCC 11.2.0, 64 bit)

This is meaningless. It's the Qt version which was used to build your QtCreator version.

How are your build folders named? In some case they are named by default like:
build_<Projectname>_<QtX_X_X>_<Compiler>_<Architecture>

There you also can find out what Qt version you are using

micha_eleric

@Pl45m4 said in QObject::connect: Cannot queue arguments of type:

@micha_eleric said in QObject::connect: Cannot queue arguments of type:

Qt Creator 6.0.2
Based on Qt 5.15.3 (GCC 11.2.0, 64 bit)

This is meaningless. It's the Qt version which was used to build your QtCreator version.

How are your build folders named? In some case they are named by default like:
build_<Projectname>_<QtX_X_X>_<Compiler>_<Architecture>

There you also can find out what Qt version you are using

again nothing of use, "build-GraphicsView-Desktop-Debug"

micha_eleric

@micha_eleric well, after pecking around, i found:
Qt 4.8.7 in PATH (qt4) /usr/lib/x86_64-linux-gnu/qt4/bin/qmake
Qt 5.15.3 in PATH (qt5) /usr/lib/qt5/bin/qmake
Qt 5.15.3 in PATH (System) /usr/bin/qmake

micha_eleric

i found another post that said to add

Q_DECLARE_METATYPE(QList<qfloat16>)

but still gave same error while running.

ChrisW67

@micha_eleric If you are on Ubuntu 22.04 (a guess on my part), have not installed a Qt version separately from that installed by Ubuntu, and everything is up-to-date then you are using Qt 5.15.3.

Open a terminal and type qmake -v

micha_eleric

@ChrisW67 said in QObject::connect: Cannot queue arguments of type:

@micha_eleric If you are on Ubuntu 22.04 (a guess on my part), have not installed a Qt version separately from that installed by Ubuntu, and everything is up-to-date then you are using Qt 5.15.3.

Open a terminal and type qmake -v

QMake version 3.1
Using Qt version 5.15.3 in /usr/lib/x86_64-linux-gnu