Qt - No matching function to call to connect

Question

I have this error when I tried to call connect.

E:\GraphTool\graphscene.cpp:7: error: no matching function for call to 'GraphScene::connect(QObject*&, void (MainWindow::)(Mode), GraphScene, void (GraphScene::*)(Mode))' QObject::connect(parent, &MainWindow::changedMode, this, &GraphScene::setMode);

I called connect in graphscene.cpp

    GraphScene::GraphScene(QObject *parent) : QGraphicsScene (parent), mode(NAV) {
        QObject::connect(parent, &MainWindow::changedMode, this, &GraphScene::setMode);
    }

The GraphScene class :

class GraphScene : public QGraphicsScene {
    Q_OBJECT
public:
    GraphScene(QObject *);
    void mousePressEvent(QGraphicsSceneMouseEvent*);

public slots:
    void setMode(Mode m);

private:
    Mode mode;
}

The MainWindow class :

class MainWindow : public QMainWindow {
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

public slots:
    void actionTriggered(QAction *action);

signals:
    void changedMode(Mode newMode);

private:
    Ui::MainWindow *ui;
    QActionGroup* modesGroup;
    GraphScene *scene;
};

I emit the signal here, I don't know if that have anything to do with it :

 void MainWindow::actionTriggered(QAction *action){
    QString actionText = action->text() ;
    if(actionText == "Navigation"){
        emit changedMode(NAV);
    }
    else if (actionText == "Add node") {
        emit changedMode(ADD_NODE);
    }
    else if (actionText == "Delete node") {
        emit changedMode(DEL_NODE);
    }
}

I found many other answers on SO related but I couldn't fix it. Most tell to check for QObject inheritance and Q_OBJECT macro.

Have you tried sending a MainWindow* to the ctor instead? I think it is failing to map the sender function to its object:cppGraphScene::GraphScene(MainWindow *parent) : QGraphicsScene (parent), mode(NAV) { QObject::connect(parent, &MainWindow::changedMode, this, &GraphScene::setMode); } — Tupaschoal
I realised the use of signals and slots is uncalled for in my case (I can just call directly). But I'm still curious why it didn't work. — Haj Ayed Amir
See my edit above, though I apologize for not writing it prettier — Tupaschoal

Tupaschoal Tupaschoal · Accepted Answer · 2019-01-27T13:44:47

Have you tried sending a MainWindow* to the ctor instead? I think it is failing to map the sender function to its object:

GraphScene::GraphScene(MainWindow *parent)
    : QGraphicsScene (parent), mode(NAV)
{
    QObject::connect(parent, &MainWindow::changedMode, this, &GraphScene::setMode);
}

Qt - No matching function to call to connect

1 Answers