Quiting Qt app by Alert Message

[Vineela]

Well yes i've marked now and by the way i've added qDebug to check what happens ,well this is what happened ..

void QWidget::keyPressEvent (QKeyEvent* event) {
     if (event->key () == Qt::Key_Back) {
          qDebug()<<"11111";
           int ret = QMessageBox::warning(this, tr("My Application"),
                               tr("About to close the app.\n"
                                  "Do you want to continue?"),

                               QMessageBox::Ok | QMessageBox::Cancel);
            qDebug()<<"222222";
          if(ret == QMessageBox::Ok){
              event->accept();
              qDebug()<<"333333";
             qApp->quit();
             qDebug()<<"444444";      
          }

          return;
     } else {
     //if not back key, call the baseclass implementation
        QWidget::keyPressEvent(event);
        qDebug()<<"555555";
    }

}

Here when the app closes it just displays qDebug 111111 and 22222 from there the projects closes automatically and nothing prints except your project is dead.

[J.Hilk]

@Vineela strange, mabye the exec of QMessageBox creates unexpected behaviour in the slot.

try

void QWidget::keyPressEvent (QKeyEvent* event) {
     if (event->key () == Qt::Key_Back) {
          qDebug()<<"Do nothing for now";
          return;
     } else {
     //if not back key, call the baseclass implementation
        QWidget::keyPressEvent(event);
    }
}

If that works, you can change it to this:

void QWidget::keyPressEvent (QKeyEvent* event) {
     if (event->key () == Qt::Key_Back) {
          qDebug()<<"Exit the function first";
          QMetaObject::invokeMethod(this, [=]()->void{
                int ret = QMessageBox::warning(this, tr("My Application"),
                               tr("About to close the app.\n"
                                  "Do you want to continue?"),

                               QMessageBox::Ok | QMessageBox::Cancel);
                 if(ret == QMessageBox::Ok){
                       qApp->quit();
                 }      
          }, Qt::QueueConnection);
          return;
     } else {
     //if not back key, call the baseclass implementation
        QWidget::keyPressEvent(event);
    }
}

[Vineela]

@J.Hilk well it is Qt::QueuedConnection not Qt::QueueConnection and yes it worked then thank you so much :D but when i enter some value in line edit and click ok in android keyboard the project closes. what can i do for this now? This Key event is reacting for the Keyboard event too.

[J.Hilk]

@Vineela said in Quiting Qt app by Alert Message:

@J.Hilk well it is Qt::QueuedConnection not Qt::QueueConnection and yes it worked then thank you so much :D

Sorry my bad, I usually rely on auto completion and the text editor of the forum doesn't have that :P

but when i enter some value in line edit and click ok in android keyboard the project closes. what can i do for this now? This Key event is reacting for the Keyboard event too.

I still think that is because you don't override the keyevent properly.
At this point I'm just speculating as you havent show your actual code/class jet.
I assume your main.cpp looks like this, or similair enough

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

    MainWindow w;
    w.show();

    return a.exec();
}

That mean your top most widget is of the class MainWindow that has the base class of QMainWindow.

The overwritten keyPressEvent would than look like this:

void MainWindow::keyPressEvent (QKeyEvent* event) {
     if (event->key () == Qt::Key_Back) {
          qDebug()<<"Exit the function first";
          QMetaObject::invokeMethod(this, [=]()->void{
                int ret = QMessageBox::warning(this, tr("My Application"),
                               tr("About to close the app.\n"
                                  "Do you want to continue?"),

                               QMessageBox::Ok | QMessageBox::Cancel);
                 if(ret == QMessageBox::Ok){
                       qApp->quit();
                 }      
          }, Qt::QueuedConnection);
          return;
     } else {
     //if not back key, call the baseclass implementation
        QMainWindow::keyPressEvent(event);
    }
}

That's the setup in one of my projects and its only detecting the hardware back button.

If that's not it, you can allways call QWidget *QWidget::focusWidget() , docu,

use qobject_cast to cast the returned object/widget to QLineEdit. If the cast in not a nullptr, than do not enter the exit request.

[Vineela]

@J.Hilk yes your correct its MainWindow but when i replaced it I got an Issue which is
error: no 'void MainWindow::keyPressEvent(QKeyEvent*)' member function declared in class 'MainWindow'
void MainWindow::keyPressEvent (QKeyEvent* event) {

[J.Hilk]

@Vineela what does your MainWindow header file look like ?

especially the keyPressEvent function declaration, I would expect something like this

protected:
    void keyPressEvent (QKeyEvent* event)override;

?

[Vineela]

@J.Hilk

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{


    Q_OBJECT

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

    ~MainWindow();

[Vineela]

@J.Hilk well
protected:
void keyPressEvent (QKeyEvent* event)override;
I've added this to my header MainWindow all working awesome
thnk u so much for your kind patience .

[J.Hilk]

@Vineela
you're welcome. :)

I'm glad it's now working for you!

[Vineela]

@J.Hilk oh yes it is working great ; P