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Children QWidgets always on top of parent

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  • T Offline
    T Offline
    Tom.C Dev
    wrote on last edited by
    #1

    Hi !

    I got a main window (QMainWindow) with some children (QWidget). Those children widgets are set with the Qt::Window flag (so they stand by themselves on the desktop). However, when the main window gets the focus (e.g. by clicking on it on the desktop), all children stay on top of the main window.

    I would like the main window to appear in front of its children when it gets the focus. I tried different window flags setup but none of them worked.

    1 Reply Last reply
    0
    • mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi, and welcome
      What flags did u use on the children?
      you can try raise() on mainwindow but if u used
      Qt::WindowStaysOnTopHint on children, it might now work.

      1 Reply Last reply
      0
      • T Offline
        T Offline
        Tom.C Dev
        wrote on last edited by
        #3

        I use the following piece of code to detach children widgets from the mainwindow.

        widget->setWindowFlags( Qt::Window );
        widget->setAttribute( Qt::WA_DeleteOnClose );
        widget->show();
        

        I also tried to use the "raise" method on the mainwindow but the children don't let their parent move to the foreground.

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        0
        • Chris KawaC Offline
          Chris KawaC Offline
          Chris Kawa
          Lifetime Qt Champion
          wrote on last edited by
          #4

          Instead of overriding child behavior one by one (window flag and deletion policy) how about not making it a child in the first place?

          1 Reply Last reply
          1
          • T Offline
            T Offline
            Tom.C Dev
            wrote on last edited by
            #5

            The main window holds the application data and the children widgets operate on these data. The lifetime of the application data and the lifetime of the children widgets are both handled by the main window. By doing this, it is not possible to have a widget pointing to the application data before it has been created or after it has been destroyed since both share the same lifetime.

            However, it seems the parent/child mechanism is responsible for the memory management AND the windows z-ordering.

            XardasX 1 Reply Last reply
            0
            • XardasX Offline
              XardasX Offline
              Xardas
              wrote on last edited by
              #6

              Same problem,

              QWidget *w = new QWidget(this); 
              w->setWindowFlags(Qt::Window);
              w->setAttribute(Qt::WA_DeleteOnClose); 
              w->show();
              

              any advice?

              1 Reply Last reply
              0
              • Chris KawaC Offline
                Chris KawaC Offline
                Chris Kawa
                Lifetime Qt Champion
                wrote on last edited by
                #7

                Same advice: how about not making it a child?

                1 Reply Last reply
                1
                • T Tom.C Dev

                  The main window holds the application data and the children widgets operate on these data. The lifetime of the application data and the lifetime of the children widgets are both handled by the main window. By doing this, it is not possible to have a widget pointing to the application data before it has been created or after it has been destroyed since both share the same lifetime.

                  However, it seems the parent/child mechanism is responsible for the memory management AND the windows z-ordering.

                  XardasX Offline
                  XardasX Offline
                  Xardas
                  wrote on last edited by
                  #8

                  @Tom.C-Dev said:

                  The main window holds the application data and the children widgets operate on these data. The lifetime of the application data and the lifetime of the children widgets are both handled by the main window.

                  same problem.

                  1 Reply Last reply
                  0
                  • Chris KawaC Offline
                    Chris KawaC Offline
                    Chris Kawa
                    Lifetime Qt Champion
                    wrote on last edited by
                    #9

                    So just delete the window when the data is destroyed. If you want the window to go away when mainwindow is destroyed you can link them like this:

                    QWidget *w = new QWidget(); 
                    w->show();
                    connect(this, &QMainWindow::destroyed, w, &QWidget::deleteLater);
                    
                    XardasX 1 Reply Last reply
                    2
                    • XardasX Offline
                      XardasX Offline
                      Xardas
                      wrote on last edited by
                      #10

                      Ok, thanks for reply.

                      1 Reply Last reply
                      0
                      • Chris KawaC Chris Kawa

                        So just delete the window when the data is destroyed. If you want the window to go away when mainwindow is destroyed you can link them like this:

                        QWidget *w = new QWidget(); 
                        w->show();
                        connect(this, &QMainWindow::destroyed, w, &QWidget::deleteLater);
                        
                        XardasX Offline
                        XardasX Offline
                        Xardas
                        wrote on last edited by
                        #11

                        @Chris-Kawa said:

                        QWidget *w = new QWidget();
                        w->show();
                        connect(this, &QMainWindow::destroyed, w, &QWidget::deleteLater);

                        doesn't work, after close main window widget stays.
                        Any ideas why?

                        1 Reply Last reply
                        0
                        • Chris KawaC Offline
                          Chris KawaC Offline
                          Chris Kawa
                          Lifetime Qt Champion
                          wrote on last edited by
                          #12

                          doesn't work

                          It works fine. Just not as you think it does.
                          By default the application event loop exits when last top level window is closed ( see quitOnLastWindowClosed property).

                          The main window is destroyed only after the event loop quits (as the main function scope ends). But the event loop does not quit since there's another top level window. You can force the main winodw to be destroyed when it closes, but then you can't put it on the stack.

                          Here's a complete example:

                          int main(int argc, char *argv[])
                          {
                              QApplication a(argc, argv);
                          
                              QMainWindow* mainWindow = new QMainWindow();
                              mainWindow->setAttribute(Qt::WA_DeleteOnClose);
                          
                              QWidget* otherWidget = new QWidget();
                              QObject::connect(mainWindow, &QMainWindow::destroyed, otherWidget, &QWidget::deleteLater);
                          
                              mainWindow->show();
                              otherWidget->show();
                          
                              return a.exec();
                          }
                          
                          kshegunovK 1 Reply Last reply
                          1
                          • Chris KawaC Chris Kawa

                            doesn't work

                            It works fine. Just not as you think it does.
                            By default the application event loop exits when last top level window is closed ( see quitOnLastWindowClosed property).

                            The main window is destroyed only after the event loop quits (as the main function scope ends). But the event loop does not quit since there's another top level window. You can force the main winodw to be destroyed when it closes, but then you can't put it on the stack.

                            Here's a complete example:

                            int main(int argc, char *argv[])
                            {
                                QApplication a(argc, argv);
                            
                                QMainWindow* mainWindow = new QMainWindow();
                                mainWindow->setAttribute(Qt::WA_DeleteOnClose);
                            
                                QWidget* otherWidget = new QWidget();
                                QObject::connect(mainWindow, &QMainWindow::destroyed, otherWidget, &QWidget::deleteLater);
                            
                                mainWindow->show();
                                otherWidget->show();
                            
                                return a.exec();
                            }
                            
                            kshegunovK Offline
                            kshegunovK Offline
                            kshegunov
                            Moderators
                            wrote on last edited by kshegunov
                            #13

                            @Chris-Kawa said:

                            The main window is destroyed only after the event loop quits (as the main function scope ends). But the event loop does not quit since there's another top level window. You can force the main winodw to be destroyed when it closes, but then you can't put it on the stack.

                            Sorry for interjecting, couldn't one call the close slot on all the child widgets and still use the stack? I mean, instead of subscribing to the destroyed signal, possibly something like this?

                            class Controller : public QObject
                            {
                                 Q_OBJECT
                            
                            signals:
                                void closing();
                            
                            protected:
                                virtual bool eventFilter(QObject * watched, QEvent * event)
                                {
                                    if (event->type() == QEvent::Close)
                                        emit closing();
                                }
                            };
                            
                            int main(int argc, char *argv[])
                            {
                                QApplication a(argc, argv);
                            
                                Controller ctrl;
                            
                                QMainWindow mainWindow;
                                mainWindow.installEventFilter(&ctrl);
                            
                                QWidget otherWidget;
                                QObject::connect(&ctrl, SIGNAL(closing()), &otherWidget, SLOT(close()));
                            
                                mainWindow.show();
                                otherWidget.show();
                            
                                return QApplication::exec();
                            }
                            

                            Read and abide by the Qt Code of Conduct

                            1 Reply Last reply
                            0
                            • Chris KawaC Offline
                              Chris KawaC Offline
                              Chris Kawa
                              Lifetime Qt Champion
                              wrote on last edited by Chris Kawa
                              #14

                              @kshegunov Yup, would work too. Personally I try to trim classes when possible. Creating a specialized one when the same can be done in a one time 2 lines of connects/attribute settings seems too "Javish" to me :P
                              You would also need a separate header/cpp for the Controller cause you can't put Q_OBJECT in a .cpp file. Not worth the effort IMO.

                              But yeah, both solutions work fine and the choice is a matter of preference as to where to put responsibilities.

                              kshegunovK 1 Reply Last reply
                              1
                              • Chris KawaC Chris Kawa

                                @kshegunov Yup, would work too. Personally I try to trim classes when possible. Creating a specialized one when the same can be done in a one time 2 lines of connects/attribute settings seems too "Javish" to me :P
                                You would also need a separate header/cpp for the Controller cause you can't put Q_OBJECT in a .cpp file. Not worth the effort IMO.

                                But yeah, both solutions work fine and the choice is a matter of preference as to where to put responsibilities.

                                kshegunovK Offline
                                kshegunovK Offline
                                kshegunov
                                Moderators
                                wrote on last edited by
                                #15

                                @Chris-Kawa said:

                                Creating a specialized one when the same can be done in a one time 2 lines of connects/attribute settings seems too "Javish" to me :P

                                Right, I agree in principle, however I'd make two points:

                                1. Usually people derive from QMainWindow and use it as a controller, then the whole creating a separate class will not be needed, as an override of closeEvent is going to be sufficient.
                                2. Ordinarily, I'd have a controller class to initialize my forms anyway (I tend not to derive from the widget classes), so in this case my proposal could also work.

                                In any case, I'm just putting it as an option. ;)

                                Read and abide by the Qt Code of Conduct

                                1 Reply Last reply
                                1
                                • XardasX Offline
                                  XardasX Offline
                                  Xardas
                                  wrote on last edited by
                                  #16

                                  Thanks for solutions, but seems "doesn't work" for me.
                                  As I understand "Child" widgets always in main and create with QMainWindow, but i need something like:
                                  MainWindow->button->clicked->tcpsocket(getSomeData)->MainWindow->readData->createWidgetWithSomeData.

                                  kshegunovK 1 Reply Last reply
                                  0
                                  • XardasX Xardas

                                    Thanks for solutions, but seems "doesn't work" for me.
                                    As I understand "Child" widgets always in main and create with QMainWindow, but i need something like:
                                    MainWindow->button->clicked->tcpsocket(getSomeData)->MainWindow->readData->createWidgetWithSomeData.

                                    kshegunovK Offline
                                    kshegunovK Offline
                                    kshegunov
                                    Moderators
                                    wrote on last edited by
                                    #17

                                    @Xardas
                                    Maybe there's a misunderstanding, no one said that creating the widgets in main() is the only way. You can create them anywhere in the code. I believe Chris' suggestion is your best bet. As an example:

                                    class MainWindow : public QMainWindow
                                    {
                                        Q_OBJECT
                                    
                                        // ... some more code
                                    
                                    signals:
                                        void closed();
                                    
                                    private slots:
                                        void showDataWidget(QByteArray);
                                    
                                    protected:
                                        virtual void closeEvent(QCloseEvent *);
                                    };
                                    
                                    void MainWindow::showDataWidget(QByteArray data)
                                    {
                                        // Create the widget
                                        QWidget * dataWidget = new QWidget(); //< NO PARENT!
                                        dataWidget->setAttribute(Qt::WA_DeleteOnClose); //< Closing the window will free the memory
                                    
                                        // ... Fill up the widget's data ...
                                        
                                        QObject::connect(this, SIGNAL(closed()), dataWidget, SLOT(deleteLater()));    //< Connect the clean up routine
                                    }
                                    
                                    void MainWindow::closeEvent(QCloseEvent * event)
                                    {
                                        emit closed();
                                        QMainWindow::closeEvent(event);
                                    }
                                    

                                    This should be easy to adapt to your case.

                                    Kind regards.

                                    Read and abide by the Qt Code of Conduct

                                    XardasX 1 Reply Last reply
                                    1
                                    • kshegunovK kshegunov

                                      @Xardas
                                      Maybe there's a misunderstanding, no one said that creating the widgets in main() is the only way. You can create them anywhere in the code. I believe Chris' suggestion is your best bet. As an example:

                                      class MainWindow : public QMainWindow
                                      {
                                          Q_OBJECT
                                      
                                          // ... some more code
                                      
                                      signals:
                                          void closed();
                                      
                                      private slots:
                                          void showDataWidget(QByteArray);
                                      
                                      protected:
                                          virtual void closeEvent(QCloseEvent *);
                                      };
                                      
                                      void MainWindow::showDataWidget(QByteArray data)
                                      {
                                          // Create the widget
                                          QWidget * dataWidget = new QWidget(); //< NO PARENT!
                                          dataWidget->setAttribute(Qt::WA_DeleteOnClose); //< Closing the window will free the memory
                                      
                                          // ... Fill up the widget's data ...
                                          
                                          QObject::connect(this, SIGNAL(closed()), dataWidget, SLOT(deleteLater()));    //< Connect the clean up routine
                                      }
                                      
                                      void MainWindow::closeEvent(QCloseEvent * event)
                                      {
                                          emit closed();
                                          QMainWindow::closeEvent(event);
                                      }
                                      

                                      This should be easy to adapt to your case.

                                      Kind regards.

                                      XardasX Offline
                                      XardasX Offline
                                      Xardas
                                      wrote on last edited by
                                      #18

                                      @kshegunov
                                      Yes, misunderstanding. Thanks, work perfectly.

                                      1 Reply Last reply
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