closing child object causes parent to be closed

[fireyyouth]

@koahnig

class Dialog:public QDialog{
   Q_OBJECT;
private slots:
void on_button_clicked() {
   Dialog * dialog = new Dialog(this->parentWidget());    //share the same parent
   dialog->show();
}
public:
   Dialog(QWidget *parent = 0):
   	QDialog(parent) 
   {
   	qDebug() << "my address " << this << ", parent address " << this->parentWidget();
   	ui = new Ui::Dialog();
   	ui->setupUi(this);
   }
   ~Dialog() {
   	qDebug() << "~Dialog";
   }
private:
   Ui::Dialog *ui;
};
int main(int argc, char **argv) {
   QApplication app(argc, argv);
   Dialog a;//parent Dialog
   Dialog *b = new Dialog(&a);//child Dialog
   b->show();
   return app.exec();
}

so the main function creates two Dialogs, the parent is invisible and the child is visible. and i click the button on the child Dialog, a new Dialog pops up, at this moment if i close any one of these two Dialogs, the whole program terminates.

[mrjj]

@fireyyouth
you should try with
app.setQuitOnLastWindowClosed(false);

[fireyyouth]

@mrjj but the case here is that the application exits when there are still two windows out there, one of them visible.

[mrjj]

@fireyyouth
Yes but if only one is considered toplevel ( never tested with only Dialogs) , it would still close.
At least for testing. then we know its not due to the auto close feature.
If it stills quits, its something else.

Also you can add a a line after app.exec() and put break point on it.
That way we can see if the exit is due to normal reason or something else.

I assume you didn't not hook up anything to the quit() slot or by other means added code to end application ?

[fireyyouth]

I updated my question, please take a look

[mrjj]

@fireyyouth
and did testing with
app.setQuitOnLastWindowClosed(false);
still close the whole app ?

[fireyyouth]

no the programs hangs

[mrjj]

@fireyyouth
hangs?
The dialogs stays on screen but can no longer be clicked ?
or how hangs ?

[fireyyouth]

@mrjj I mean after closing all the dialog i can click on , the QApplication::exec() does not return.

[mrjj]

@fireyyouth
ahh, that is expected as we disable the auto close.
You must close it yourself using quit() in application.

You can use DeleteOnclose on the dialog and call QApplication::quit() in destructor.

Of Course it depends on what design you're after.
So if you do this in Dialog ( the parent), it should do as you want.

[fireyyouth]

I get what you mean and i think it could work. thanks. but I still want to understand why the original case happened, can you explain?

[mrjj]

@fireyyouth
I did not test it, but i think that a invisible dialog do not count as "window" and hence
it would auto close when you closed the dialog. ( even if not the last "window" )

You can test if the dialog is considered that.
Its normally/used to be a flag. You set. QMianwindow has it.
Not sure with Dialogs in all cases. Where parent is also a Dialog
http://doc.qt.io/qt-5/qt.html#WindowType-enum
Also I could not find the exact doc on the rules for being top level and the auto close feature.
I did find that
"QDialog and QMainWindow widgets are by default windows, even if a parent widget is specified in the constructor. This behavior is specified by the Qt::Window flag."

You could try the code, to see what is listed.

void showAllTopLevelWidgets()
{
    foreach (QWidget *widget, QApplication::topLevelWidgets()) {
      // print out info
    }
}

So overall the dialogs are not having WType_TopLevel if they have parents or something like that.
Where as QMainWindow has it.
You can give flags to Dialog in constructor so I think u can make it work like MW with some research.
I think WType_TopLevel is called something else. But not sure.
My Google fu failed me. Looking in the source code would bring light.