Signal and slot working without Q_OBJECT Macro

[Vinoth Rajendran4]

Hi All,

class MainWindow : public QMainWindow
{
   // Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

};

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    connect(ui->pushButton,SIGNAL(clicked(bool)),this,SLOT(close()));

}

Q_OBJECT macro is commented, but still signal and slot is working fine.. Can someone please help me understand how this is possible ??

[aha_1980]

@Vinoth-Rajendran4

Probably some prior generated files are still existing? It should stop working after you wiped the build folder and rebuild your program.

Regards

[Vinoth Rajendran4]

@aha_1980 , Thanks for the confirmation

[aha_1980]

@Vinoth-Rajendran4

So is you problem solved? Then please mark this topic as SOLVED too. Thanks!

[SGaist]

Hi,

You are not adding any new signal or slot to your class but using what is already available hence there's no need for the Q_OBJECT macro in your case. However as soon as you want to implement signal/slot/property into your class you will have to add that macro.

[aha_1980]

@SGaist Good catch!

[JKSH]

@SGaist said in Signal and slot working without Q_OBJECT Macro:

You are not adding any new signal or slot to your class but using what is already available hence there's no need for the Q_OBJECT macro in your case. However as soon as you want to implement signal/slot/property into your class you will have to add that macro.

Also, without the Q_OBJECT macro, this->metaObject()->className() returns the wrong class.

[VRonin]

Based on experience, not on knowledge. Treat with caution.

Q_OBJECT is necessary if:

• you declare a new signal or slot
• use qobject_cast on that class
• use the meta-object system on that class