QObject::connect: signal not found in promoted widget with Lambda syntax

[Taz742]

I have an overloaded QTreeWidget class, with my SIGNALS: I have promoted it in my UI and when I listen promoted QTreeWidget object with a lambda syntax I have an error.

QObject::connect: signal not found in CustomTreeWidget.

MY CustomTreeWidget looks like:

.h

class CustomTreeWidget : public QTreeWidget
{
    Q_OBJECT
public:
    explicit CustomTreeWidget(QWidget *parent = 0);

    ~CustomTreeWidget() {
    }

signals:
    void currentNodeChanged(QSet<int> uids);
    void deleteRequest(QVector<int> uids);
}

.cpp

CustomTreeWidget::CustomTreeWidget(QWidget *parent) : QTreeWidget(parent)
{
    setAnimated(true);

    connect(this, &CustomTreeWidget::customContextMenuRequested, this, [=](const QPoint &pos) {
        this->m_bCustomMenuOpen = true;
        const auto &&item = this->itemAt(pos);

        QMenu myMenu;

        bool ok = !(item) ? false : true;

        if (ok) {
        //თუ topLevelItem -ია მხოლოდ დამატების action -ი უნდა იყოს ჩართული.
            if (item == this->topLevelItem(0) || item == this->topLevelItem(0)->child(0)) {
                ok = false;
            }
        }

        QAction *Removecnt = myMenu.addAction(tr("&წაშლა"), this, SLOT(DeleteNode()));
        Removecnt->setIcon(QIcon(":/global_res/delete.png"));
        Removecnt->setEnabled(ok);

        myMenu.exec(this->mapToGlobal(pos));
    });
}

void CustomTreeWidget::BFS(QTreeWidgetItem *item, QSet<int> &out)
{
    std::queue<QTreeWidgetItem *> Q;
    Q.push(item);

    while (!Q.empty()) {
        QTreeWidgetItem *now = Q.front(); Q.pop();
        out.insert(this->m_mapUids[now]);
        for (int i = 0; i < now->childCount(); i++) {
            Q.push(now->child(i));
        }
    }
}

QSet<int> CustomTreeWidget::GetCurrentNodeUids()
{
    QSet<int> uids;
    if (!this->currentItem())
        return uids;

    this->BFS(this->currentItem(), uids);
    return uids;
}

void CustomTreeWidget::DeleteNode()
{
    QSet<int> nodes = this->GetCurrentNodeUids();
    QVector<int> uids;
    for (auto it : nodes) {
        uids.push_back(it);
    }

    emit deleteRequest(uids);
}

My lambda looks like:

connect(ui->productTree, &CustomTreeWidget::deleteRequest, this, [=](QVector<int> uids) {
    //logic
});

But this signal works with old syntax.

connect(ui->productTree, SIGNAL(deleteRequest(QVector<int>)), this, SLOT(checkSlot(QVector<int>)));

And this slot is.

void ProductForm::checkSlot(QVector<int> uids)
{
    qDebug() << uids.size();
}

So what is problem lambda syntax?

[VRonin]

Did you include the header of CustomTreeWidget in the ProductForm source file?

[Taz742]

@VRonin
Yes i have.

[VRonin]

There's nothing wrong in the code you posted, they only thing I can think of is try using QOverload<>::of in case that's the source of the problem

[Taz742]

@VRonin
Something like this?

connect(ui->productTree, static_cast<void (CustomTreeWidget::*)(QVector<int>)>(&CustomTreeWidget::deleteRequest), this, [=](QVector<int> uids) {
    qDebug() << "yeapp";
});

or

connect(ui->productTree, QOverload<QVector<int>>::of(&CustomTreeWidget::deleteRequest), this, [=](QVector<int> uids) {
    qDebug() << "yeapp";
});

Everything is same.

[JKSH]

Quick test: Create a dummy class that inherits QObject (not a promoted QWidget!) and also give it a signal void deleteRequest(QVector<int> uids). Instantiate this dummy class and try to connect this dummy signal to your lambda.

Does it work?

[Taz742]

Guys... I dont know why but my CustomTreeWidget class have a UI. Should it be? :D

[jsulm]

@Taz742 said in QObject::connect: signal not found in promoted widget with Lambda syntax:

I dont know why but my CustomTreeWidget class have a UI

What do you mean? It is a GUI class, so it has a UI. Or do you mean it has ui member variable?

[J.Hilk]

Hi,
have you registered QVector as a metatype - using qRegisterMetaType, to use it via Signal/Slots?

[Taz742]

@J.Hilk
In main.cpp

    qRegisterMetaType<QVector<int>>("QVector<int>");

Now i am tryng but have a same situation.

[SGaist]

Hi,

here's a dummy example:

#include <QtCore>
#include <QtDebug>

class MyClass : public QObject
{
    Q_OBJECT

signals:
    void deleteRequest(QVector<int> uids);
    void done();

public slots:
    void trigger()
    {
        emit deleteRequest(QVector<int>{1, 2, 3, 4});
        QTimer::singleShot(1000, this, &MyClass::done);
    }
};

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

    MyClass mc;
    QTimer::singleShot(1000, &mc, &MyClass::trigger);
    QObject::connect(&mc, &MyClass::done, qApp, &QCoreApplication::quit);
    QObject::connect(&mc, &MyClass::deleteRequest, [](const QVector<int>& data) { qDebug() << data; });
    return app.exec();
}

#include "main.moc"

The content of the QVector is printed after one second and the application ends after another one. Does it work on your machine ?

[Taz742]

@SGaist
Yes its work. I am also tryed to create new project, move my CustomTreeWidget and work there.

[Taz742]

@SGaist
I have a same situation in other class.
Can you check this example?

#ifndef IMAGEWORKER_H
#define IMAGEWORKER_H

#include <QObject>
#include "QDebug"
#include "globalhelper.h"
#include "QThread"
#include "QMutex"
#include "QFile"
#include "QDir"
#include "QCryptographicHash"
#include "QByteArray"

class ImageWorker : public QObject
{
    Q_OBJECT
public:
    explicit ImageWorker(QObject *parent = 0) {
        Q_UNUSED(parent);
        QThread *thread = new QThread;
        this->moveToThread(thread);
        connect(thread, &QThread::started, this, &ImageWorker::doWork);
        connect(this, &ImageWorker::finished, thread, &QThread::quit);
        connect(this, &ImageWorker::finished, this, &ImageWorker::deleteLater);
        connect(thread, &QThread::finished, thread, &QThread::deleteLater);
        thread->start();
    }

    ~ImageWorker() {
        qDebug() << "ImageWorker deleted";
    }

signals:
    void finished();

public slots:
    void doWork() {
        emit finished();
    }

private:
    bool compareImages(const QByteArray &myImage, const QByteArray &serverImage) const
    {
        return myImage.toHex() == serverImage.toHex();
    }

    QByteArray fileChecksum(const QByteArray &bytes, QCryptographicHash::Algorithm hashAlgorithm = QCryptographicHash::Md5) const
    {
        QCryptographicHash hash(hashAlgorithm);
        hash.addData(bytes);
        return hash.result();
    }

};


#endif // IMAGEWORKER_H

[SGaist]

Since you implement the constructor in your derived class, why don't you call the base class constructor ?

What exact situation do you have ?

[Taz742]

@SGaist said in QObject::connect: signal not found in promoted widget with Lambda syntax:

Since you implement the constructor in your derived class, why don't you call the base class constructor ?

I dont understood...

@SGaist said in QObject::connect: signal not found in promoted widget with Lambda syntax:

What exact situation do you have ?

QObject::connect: signal not found in ImageWorker
QObject::connect: signal not found in ImageWorker

I am debuging it and its happen here:

        connect(this, &ImageWorker::finished, thread, &QThread::quit);
        connect(this, &ImageWorker::finished, this, &ImageWorker::deleteLater);

[SGaist]

explicit ImageWorker(QObject *parent = 0)
        : QObject(parent)
    {
        QThread *thread = new QThread;
       etc.

I removed #include "globalhelper.h" and it build successfully on macOS.

[Taz742]

@SGaist
There is great uncertainty... I changed

@Taz742 said in QObject::connect: signal not found in promoted widget with Lambda syntax:

    connect(this, &ImageWorker::finished, thread, &QThread::quit);
    connect(this, &ImageWorker::finished, this, &ImageWorker::deleteLater);

to

        connect(this, SIGNAL(workerFinished()), thread, SLOT(quit()));
        connect(this, SIGNAL(workerFinished()), this, SLOT(deleteLater()));

its work...