Qt: How do I handle the event of the user pressing the 'X' (close) button?

Question

In Qt, what is the slot that corresponds to the event of the user clicking the 'X' (close) button of the window frame i.e. this button:

Close button of the window

If there isn't a slot for this, is there any other way to trigger a function after the user presses the close button?

score 203 · Accepted Answer · edited Jul 19 '16 at 20:39

203

If you have a QMainWindow you can override closeEvent method.

#include <QCloseEvent>
void MainWindow::closeEvent (QCloseEvent *event)
{
    QMessageBox::StandardButton resBtn = QMessageBox::question( this, APP_NAME,
                                                                tr("Are you sure?\n"),
                                                                QMessageBox::Cancel | QMessageBox::No | QMessageBox::Yes,
                                                                QMessageBox::Yes);
    if (resBtn != QMessageBox::Yes) {
        event->ignore();
    } else {
        event->accept();
    }
}

If you're subclassing a QDialog, the closeEvent will not be called and so you have to override reject():

void MyDialog::reject()
{
    QMessageBox::StandardButton resBtn = QMessageBox::Yes;
    if (changes) {
        resBtn = QMessageBox::question( this, APP_NAME,
                                        tr("Are you sure?\n"),
                                        QMessageBox::Cancel | QMessageBox::No | QMessageBox::Yes,
                                        QMessageBox::Yes);
    }
    if (resBtn == QMessageBox::Yes) {
        QDialog::reject();
    }
}

edited Jul 19 '16 at 20:39

Jason Sundram

12,225
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answered Jul 05 '13 at 06:53

asclepix

7,971
3
31
41

1

You may want to also use `setAttribute(Qt::WA_QuitOnClose);` for MainWindow. – Borzh Nov 22 '15 at 17:14
Are you sure that subclassing QDialog will not call `closeEvent`? It works for me, and the documentation of [QCloseEvent](http://doc.qt.io/qt-5/qcloseevent.html) says that *The event handler QWidget::closeEvent() receives close events* and QDialog is also a Widget right? Or is it related to older Qt version (<5.x) somehow? – Dimitri Podborski Mar 30 '16 at 10:17
2

@incBrain Even in Qt 4.8 the 'X' button calls `closeEvent` in a QDialog, but if the user press _Esc_ on the keyboard the QDialog is closed without calling `closeEvent`. – asclepix Mar 31 '16 at 09:57
@asclepix thanks for clarification. So basically overwriting `reject` function would be the right move to solve this problem. I've found this sentence in the documentation: *In order to modify your dialog's close behavior, you can reimplement the functions accept(), reject() or done(). The `closeEvent()` function should only be reimplemented to preserve the dialog's position or to override the standard close or reject behavior* – Dimitri Podborski Mar 31 '16 at 10:25
Another way would be to connect to *rejected* signal of QDialog. – JeFf Mar 14 '18 at 14:42

score 22 · Answer 2 · edited Nov 11 '16 at 18:55

22

Well, I got it. One way is to override the QWidget::closeEvent(QCloseEvent *event) method in your class definition and add your code into that function. Example:

class foo : public QMainWindow
{
    Q_OBJECT
private:
    void closeEvent(QCloseEvent *bar);
    // ...
};


void foo::closeEvent(QCloseEvent *bar)
{
    // Do something
    bar->accept();
}

edited Nov 11 '16 at 18:55

waldyrious

3,683
4
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answered Jul 05 '13 at 04:46

Shravan

2,809
2
18
39

score 16 · Answer 3 · answered Jul 05 '13 at 10:44

16

You can attach a SLOT to the

void aboutToQuit();

signal of your QApplication. This signal should be raised just before app closes.

answered Jul 05 '13 at 10:44

Sebastian Lange

3,879
1
19
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3

We used it kind of: ``connect(qApp,SIGNAL(aboutToQuit()),this,SLOT(quitMyApp()));`` – Sebastian Lange Jul 10 '13 at 06:24
4

However, [quote from the documentation](http://doc.qt.io/qt-5/qcoreapplication.html#aboutToQuit): "Note that no user interaction is possible in this state." – Ignitor Dec 07 '15 at 11:02
It works for me, but note that unlike reimplementing QMainWindow::closeEvent(), you cannot cancel application closing. – Valentin Safonnikov Aug 25 '22 at 06:40

score 12 · Answer 4 · answered Nov 27 '15 at 09:44

12

also you can reimplement protected member QWidget::closeEvent()

void YourWidgetWithXButton::closeEvent(QCloseEvent *event)
{
    // do what you need here
    // then call parent's procedure
    QWidget::closeEvent(event);
}

answered Nov 27 '15 at 09:44

Alexander

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1
2

score 0 · Answer 5 · answered May 13 '23 at 17:34

To capture the event of the close button being pressed without deriving from QWidget and the sort, you could use an event filter.

Here's a simple demonstration, using a simple application that displays a QWidget:

If you use QWidget itself, you need to capture QEvent::Close:

#include "myEventFilter.h"
#include <QApplication>
#include <QWidget>

int main(int argc,char*argv[])
{
    QApplication a(argc, argv);
    
    w.installEventFilter(filter);
    
    QWidget *w = new QWidget();

    //install the event filter on the widget
    w->installEventFilter(filter);

    w->show();

    return a.exec();
}

Event filter:

#ifndef MYEVENTFILTER_H
#define MYEVENTFILTER_H

#include <QObject>
#include <QDebug>
#include <QEvent>

class myEventFilter : public QObject
{
    Q_OBJECT

public:
    myEventFilter (QObject *parent = nullptr) {}

protected:
    bool eventFilter(QObject * obj, QEvent * event) override
    {
        if (event->type() == QEvent::Close)
        {
            //handle the event here
            qDebug()<<"out";
           //In case you need the QWidget itself 
           QWidget *w = static_cast<QWidget*>(obj);
        }

        return QObject::eventFilter(obj, event);
    }
};

#endif // MYEVENTFILTER_H

If you use QApplication's object, you need to capture QEvent::Quit:

#include <QApplication>
#include "myEventFilter.h"

int main(int argc,char*argv[])
{
    QApplication a(argc, argv);

    QWidget *w = new QWidget();

    myEventFilter *filter = new myEventFilter();

    //install the event filter on QApplication object
    a.installEventFilter(filter);

    w->show();

    return a.exec();
}

Event filter

#ifndef MYEVENTFILTER_H
#define MYEVENTFILTER_H

#include <QObject>
#include <QDebug>
#include <QEvent>
#include <QLineEdit>

class myEventFilter : public QObject
{
    Q_OBJECT

public:
    myEventFilter (QObject *parent = nullptr) {}

protected:
    bool eventFilter(QObject * obj, QEvent * event) override
    {
        if (event->type() == QEvent::Quit)
        {
            //handle the event here as well
            qDebug()<<"out";
        }

        return QObject::eventFilter(obj, event);
    }
};

#endif // MYEVENTFILTER_H

score 0 · Answer 6 · answered Aug 01 '23 at 05:55

0

The simple way to close properly using QCloseEvent.

void MainWindow::closeEvent (QCloseEvent *)
{
    QCoreApplication::quit();
}

answered Aug 01 '23 at 05:55

Shaiful Islam

335
2
12

Qt: How do I handle the event of the user pressing the 'X' (close) button?

6 Answers6

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