close QMessageBox when certain condition is fulfilled

Question

This is working:

#ifndef MYWARMUPMESSAGEBOX_H
#define MYWARMUPMESSAGEBOX_H

#include <QMessageBox>
#include <QPushButton>
#include <QTimer>

class myWarmUpMessageBox : public QMessageBox
{
    Q_OBJECT

private:

   QString _text;
   int _timeoutSeconds;
   QTimer _timer;
   int num = 0;

public:
explicit myWarmUpMessageBox(QWidget * parent):
   QMessageBox(parent)
   {
       connect(&_timer, SIGNAL(timeout()), this, SLOT(updateText()));
       _timer.start(500);
   }

   virtual void showEvent(QShowEvent * e)
   {
       QMessageBox::showEvent(e);
       updateText();
   }

public slots:

void updateText()
{
    num+=1;
    setText(QString::number(num));

    if(num>3)
        this->close();
}

I am using this QMessageBox in a QMainWindow in its close event.

void MainWindow::closeEvent(QCloseEvent *event)
{
    myWarmUpMessageBox * myBox = new myWarmUpMessageBox(this);
    myBox->exec();
    event->accept();
}

The QMessageBox pops up, counts to 3 diappears, and subsenquently the QMainWindow closes.

BUT it is not working if the condition for closing is fulfilled immediately, i.e. when saying

if(num>0)
    this->close();

which is true when the timer is triggered the first time, the program brakes. Why???

Answer 1

You have to let the QMessageBox to open fully and maximized and then only you need to close it, otherwise the QMessageBox Dialog may not be registered/fully loaded yet, for the close function to be successful.

same goes for closeevent also, if you try to access any Dialog widget properties inside Dialog closeevent.