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Confusion between the usage of 'this' and 'parent'

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  • JKSHJ JKSH

    @Swati777999 said in Confusion between the usage of 'this' and 'parent':

    OK, and what happens when you set nullptr as a widget's parent? (Hint: Your LayoutExample object also has nullptr as its parent)

    When the widget's parent is set to null, that means it has no parent,

    Correct.

    maybe it starts acting as a parent.

    That's not quite right. When a widget has no parent, it can act as a top-level window (say "top-level window", not "parent"). That means whenever you call show() on a widget that has no parent, then that widget appears in a new window.

    // button1 and button2 have a parent, and will appear inside your widget
    button1 = new QPushButton("Click Here", this);
    button2 = new QPushButton("Sign up",this);
    
    // button3 has no parent, and will open in a new window
    button3 = new QPushButton("Hello");
    button3->show(); // If you don't call show(), button3 will be invisible
    
    Swati777999S Offline
    Swati777999S Offline
    Swati777999
    wrote on last edited by Swati777999
    #34

    @JKSH said in Confusion between the usage of 'this' and 'parent':

    @Swati777999 said in Confusion between the usage of 'this' and 'parent':

    button1 and button2 appear on the window because I have used this->show() at the end.

    // button1 and button2 have a parent, and will appear inside your widget
    button1 = new QPushButton("Click Here", this);
    button2 = new QPushButton("Sign up",this);
    
    // button3 has no parent, and will open in a new window
    button3 = new QPushButton("Hello");
    button3->show(); // If you don't call show(), button3 will be invisible
    

    I am not worried about button3, all I am concerned about is quit button of main.cpp file.

    I made following change in main.cpp

    quit.move(80,80)
    

    and w.show() is already there in main.cpp

    Then, why isn't quit button showing up in my window whereas other two buttons signup and 'Click Here' appear?

    “ In order to be irreplaceable, one must always be different” – Coco Chanel

    JKSHJ 1 Reply Last reply
    0
    • S Offline
      S Offline
      SimonSchroeder
      wrote on last edited by
      #35

      You shouldn't move and resize widgets (buttons are also widgets) when you want to use layouts. Layouts will position and resize all their widgets themselves. Most likely layouts will override everything else in the end.

      When you are using a QGridLayout you should always specify the row and column. I am not sure what would happen otherwise. Only with the box layouts it makes sense to not specify a position in the layout as they will then only be appended (to the right in horizontal layouts or to the bottom in vertical layouts).

      About the parents in Qt: Unfortunately, it is a little bit more confusing when you are using layouts than what you have discussed so far. Whenever you add a widget to a layout it will be reparented to the layout's parent. The reason behind this is that for widgets the parent-child relationship also applies to the visual representation. When you show a parent all its children will be shown as well. I personally don't provide a parent when creating child objects (like in new QPushButton("Button")) but rely on the parent being set when I add widgets to a layout (and I exclusively use layouts instead of fixed positioning). Though this is just my personal preference.

      1 Reply Last reply
      1
      • Swati777999S Swati777999

        @JKSH said in Confusion between the usage of 'this' and 'parent':

        @Swati777999 said in Confusion between the usage of 'this' and 'parent':

        button1 and button2 appear on the window because I have used this->show() at the end.

        // button1 and button2 have a parent, and will appear inside your widget
        button1 = new QPushButton("Click Here", this);
        button2 = new QPushButton("Sign up",this);
        
        // button3 has no parent, and will open in a new window
        button3 = new QPushButton("Hello");
        button3->show(); // If you don't call show(), button3 will be invisible
        

        I am not worried about button3, all I am concerned about is quit button of main.cpp file.

        I made following change in main.cpp

        quit.move(80,80)
        

        and w.show() is already there in main.cpp

        Then, why isn't quit button showing up in my window whereas other two buttons signup and 'Click Here' appear?

        JKSHJ Offline
        JKSHJ Offline
        JKSH
        Moderators
        wrote on last edited by
        #36

        @Swati777999 said in Confusion between the usage of 'this' and 'parent':

        Then, why isn't quit button showing up in my window whereas other two buttons signup and 'Click Here' appear?

        I agree with @SimonSchroeder: Since your top-level widget has a layout, do not add a child widget that is not part of that layout. It is not designed to work that way.

        Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

        Swati777999S 1 Reply Last reply
        0
        • JKSHJ JKSH

          @Swati777999 said in Confusion between the usage of 'this' and 'parent':

          Then, why isn't quit button showing up in my window whereas other two buttons signup and 'Click Here' appear?

          I agree with @SimonSchroeder: Since your top-level widget has a layout, do not add a child widget that is not part of that layout. It is not designed to work that way.

          Swati777999S Offline
          Swati777999S Offline
          Swati777999
          wrote on last edited by
          #37

          @JKSH

          What do you mean by top-level widget? Is it the one declared in main.cpp ; i.e quit button?

          “ In order to be irreplaceable, one must always be different” – Coco Chanel

          JKSHJ 1 Reply Last reply
          0
          • Swati777999S Swati777999

            @JKSH

            What do you mean by top-level widget? Is it the one declared in main.cpp ; i.e quit button?

            JKSHJ Offline
            JKSHJ Offline
            JKSH
            Moderators
            wrote on last edited by JKSH
            #38

            @Swati777999 said in Confusion between the usage of 'this' and 'parent':

            @JKSH

            What do you mean by top-level widget? Is it the one declared in main.cpp ; i.e quit button?

            A top-level widget is a widget that has its own window.

            In your code, button1 and button2 are not top-level widgets because they don't have their own windows. Instead, they are inside w's window.

            Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

            1 Reply Last reply
            1
            • Swati777999S Swati777999

              @Christian-Ehrlicher
              There's only one example in the documentation.

              The following code is something I tried on my own.

              layoutexample.h

              #ifndef LAYOUTEXAMPLE_H
              #define LAYOUTEXAMPLE_H
              
              #include <QMainWindow>
              #include <QWidget>
              #include <QTableWidget>
              #include <QGridLayout>
              #include <QPushButton>
              #include <QMenuBar>
              
              class LayoutExample : public QMainWindow
              {
                  Q_OBJECT
                  QWidget *box;
                  QGridLayout *gridLay;
                  QPushButton *button1;
                  QPushButton *button2;
              
              public:
                  LayoutExample(QWidget *parent=nullptr);
                  ~LayoutExample();
              };
              #endif // LAYOUTEXAMPLE_H
              
              

              layoutexample.cpp

              #include "layoutexample.h"
              #include <QGridLayout>
              #include <QWidget>
              #include <QTableWidget>
              #include <QPushButton>
              #include <QMenuBar>
              
              LayoutExample::LayoutExample(QWidget *parent)
                  : QMainWindow(parent)
              {
                  box = new QWidget();
                  button1=new QPushButton("Click Here");
                  button2 = new QPushButton("Sign up");
                  gridLay = new QGridLayout();
                  box->setFixedSize(100,100);
              
                  gridLay->setRowMinimumHeight(5,4);
                  gridLay->setHorizontalSpacing(20);
                  gridLay->addWidget(box);
                  gridLay->addWidget(button1);
                  gridLay->addWidget(button2);
              
                  this->setLayout(gridLay);
                  //this->parentWidget()->setLayout(gridLay);
              }
              
              LayoutExample::~LayoutExample()
              {
              }
              
              

              In the above code, in place of 'this' when I write parent , my program crashes. This code does not add widgets to the main window. Only the effects of codes of main.cpp are reflected in the main window.

              How can I use w parent Qobject from main.cpp in layout.cpp? [I am so confused about the structure of writing codes in these 3 files and parent-child implementation]

              Does parent in layout.cpp refer to w ?
              main.cpp

              #include "layoutexample.h"
              
              #include <QApplication>
              #include <QWidget>
              #include <QTableWidget>
              #include <QMenuBar>
              
              
              int main(int argc, char *argv[])
              {
                  QApplication a(argc, argv);
              
                  LayoutExample w;  // w: parent QObject
                  QPushButton quit("Quit",&w);      // quit: child QObject
                  quit.move(100,100); // x and y coordinates of widgets wrt to the mainwindow
                  w.setWindowTitle("Layout Example");
                  quit.setBaseSize(100,100);
                  quit.setAutoFillBackground("yes");
              
                  QGridLayout grid(&w);    
                 //w.setLayout(grid);
              
                  w.show();
                  return a.exec();
              }
              
              }
              

              Edit: I've changed the name of the project from layout to layoutExample to avoid confusion.

              Swati777999S Offline
              Swati777999S Offline
              Swati777999
              wrote on last edited by
              #39

              @Swati777999 said in Confusion between the usage of 'this' and 'parent':

              @Christian-Ehrlicher
              There's only one example in the documentation.

              The following code is something I tried on my own.

              layoutexample.h

              #ifndef LAYOUTEXAMPLE_H
              #define LAYOUTEXAMPLE_H
              
              #include <QMainWindow>
              #include <QWidget>
              #include <QTableWidget>
              #include <QGridLayout>
              #include <QPushButton>
              #include <QMenuBar>
              
              class LayoutExample : public QMainWindow
              {
                  Q_OBJECT
                  QWidget *box;
                  QGridLayout *gridLay;
                  QPushButton *button1;
                  QPushButton *button2;
              
              public:
                  LayoutExample(QWidget *parent=nullptr);
                  ~LayoutExample();
              };
              #endif // LAYOUTEXAMPLE_H
              
              

              layoutexample.cpp

              #include "layoutexample.h"
              #include <QGridLayout>
              #include <QWidget>
              #include <QTableWidget>
              #include <QPushButton>
              #include <QMenuBar>
              
              LayoutExample::LayoutExample(QWidget *parent)
                  : QMainWindow(parent)
              {
                  box = new QWidget();
                  button1=new QPushButton("Click Here");
                  button2 = new QPushButton("Sign up");
                  gridLay = new QGridLayout();
                  box->setFixedSize(100,100);
              
                  gridLay->setRowMinimumHeight(5,4);
                  gridLay->setHorizontalSpacing(20);
                  gridLay->addWidget(box);
                  gridLay->addWidget(button1);
                  gridLay->addWidget(button2);
              
                  this->setLayout(gridLay);
                  //this->parentWidget()->setLayout(gridLay);
              }
              
              LayoutExample::~LayoutExample()
              {
              }
              
              

              In the above code, in place of 'this' when I write parent , my program crashes. This code does not add widgets to the main window. Only the effects of codes of main.cpp are reflected in the main window.

              How can I use w parent Qobject from main.cpp in layout.cpp? [I am so confused about the structure of writing codes in these 3 files and parent-child implementation]

              Does parent in layout.cpp refer to w ?
              main.cpp

              #include "layoutexample.h"
              
              #include <QApplication>
              #include <QWidget>
              #include <QTableWidget>
              #include <QMenuBar>
              
              
              int main(int argc, char *argv[])
              {
                  QApplication a(argc, argv);
              
                  LayoutExample w;  // w: parent QObject
                  QPushButton quit("Quit",&w);      // quit: child QObject
                  quit.move(100,100); // x and y coordinates of widgets wrt to the mainwindow
                  w.setWindowTitle("Layout Example");
                  quit.setBaseSize(100,100);
                  quit.setAutoFillBackground("yes");
              
                  QGridLayout grid(&w);    
                 //w.setLayout(grid);
              
                  w.show();
                  return a.exec();
              }
              
              }
              

              Edit: I've changed the name of the project from layout to layoutExample to avoid confusion.

              @JKSH
              Another observation here,
              In layoutExample.cpp , [ in main.cpp , w.show() is present as it is ]
              CASE-1
              In the presence of

              this->show();
              
              

              following result is obtained ;
              Layout_Example3.PNG

              CASE-2
              When I comment

              //this->show();
              

              I get the following result
              layout_Example2.PNG

              My doubt here is ; in CASE-2, why should these buttons; Sign up and Click Here appear as this->show() is commented?

              In CASE-1 , why does quit button from main.cpp appear in the same window?

              Please explain the reason.

              Thanks!

              “ In order to be irreplaceable, one must always be different” – Coco Chanel

              Pl45m4P 1 Reply Last reply
              0
              • Swati777999S Swati777999

                @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                @Christian-Ehrlicher
                There's only one example in the documentation.

                The following code is something I tried on my own.

                layoutexample.h

                #ifndef LAYOUTEXAMPLE_H
                #define LAYOUTEXAMPLE_H
                
                #include <QMainWindow>
                #include <QWidget>
                #include <QTableWidget>
                #include <QGridLayout>
                #include <QPushButton>
                #include <QMenuBar>
                
                class LayoutExample : public QMainWindow
                {
                    Q_OBJECT
                    QWidget *box;
                    QGridLayout *gridLay;
                    QPushButton *button1;
                    QPushButton *button2;
                
                public:
                    LayoutExample(QWidget *parent=nullptr);
                    ~LayoutExample();
                };
                #endif // LAYOUTEXAMPLE_H
                
                

                layoutexample.cpp

                #include "layoutexample.h"
                #include <QGridLayout>
                #include <QWidget>
                #include <QTableWidget>
                #include <QPushButton>
                #include <QMenuBar>
                
                LayoutExample::LayoutExample(QWidget *parent)
                    : QMainWindow(parent)
                {
                    box = new QWidget();
                    button1=new QPushButton("Click Here");
                    button2 = new QPushButton("Sign up");
                    gridLay = new QGridLayout();
                    box->setFixedSize(100,100);
                
                    gridLay->setRowMinimumHeight(5,4);
                    gridLay->setHorizontalSpacing(20);
                    gridLay->addWidget(box);
                    gridLay->addWidget(button1);
                    gridLay->addWidget(button2);
                
                    this->setLayout(gridLay);
                    //this->parentWidget()->setLayout(gridLay);
                }
                
                LayoutExample::~LayoutExample()
                {
                }
                
                

                In the above code, in place of 'this' when I write parent , my program crashes. This code does not add widgets to the main window. Only the effects of codes of main.cpp are reflected in the main window.

                How can I use w parent Qobject from main.cpp in layout.cpp? [I am so confused about the structure of writing codes in these 3 files and parent-child implementation]

                Does parent in layout.cpp refer to w ?
                main.cpp

                #include "layoutexample.h"
                
                #include <QApplication>
                #include <QWidget>
                #include <QTableWidget>
                #include <QMenuBar>
                
                
                int main(int argc, char *argv[])
                {
                    QApplication a(argc, argv);
                
                    LayoutExample w;  // w: parent QObject
                    QPushButton quit("Quit",&w);      // quit: child QObject
                    quit.move(100,100); // x and y coordinates of widgets wrt to the mainwindow
                    w.setWindowTitle("Layout Example");
                    quit.setBaseSize(100,100);
                    quit.setAutoFillBackground("yes");
                
                    QGridLayout grid(&w);    
                   //w.setLayout(grid);
                
                    w.show();
                    return a.exec();
                }
                
                }
                

                Edit: I've changed the name of the project from layout to layoutExample to avoid confusion.

                @JKSH
                Another observation here,
                In layoutExample.cpp , [ in main.cpp , w.show() is present as it is ]
                CASE-1
                In the presence of

                this->show();
                
                

                following result is obtained ;
                Layout_Example3.PNG

                CASE-2
                When I comment

                //this->show();
                

                I get the following result
                layout_Example2.PNG

                My doubt here is ; in CASE-2, why should these buttons; Sign up and Click Here appear as this->show() is commented?

                In CASE-1 , why does quit button from main.cpp appear in the same window?

                Please explain the reason.

                Thanks!

                Pl45m4P Offline
                Pl45m4P Offline
                Pl45m4
                wrote on last edited by Pl45m4
                #40

                @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                In CASE-1 , why does quit button from main.cpp appear in the same window?

                Because you've set w as parent of your quit button. So it appears in parent coodinates. If you remove the &w from your quit button's c'tor and still move it to, say (100, 100) and show it afterwards, it should appear as standalone widget at 100,100 from TOP-LEFT corner of your SCREEN.

                Btw: You should really use your layouts, not create them and then just throw your widgets (buttons) on your parent (LayoutExample window/widget) without actually putting them in a layout.

                CASE 2

                where is your this->show() located?! Cant tell right now...
                The other 2 buttons are there because they are children of LayoutExample widget.... and you still show it with w.show() in your main()


                If debugging is the process of removing software bugs, then programming must be the process of putting them in.

                ~E. W. Dijkstra

                Swati777999S 2 Replies Last reply
                1
                • Pl45m4P Pl45m4

                  @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                  In CASE-1 , why does quit button from main.cpp appear in the same window?

                  Because you've set w as parent of your quit button. So it appears in parent coodinates. If you remove the &w from your quit button's c'tor and still move it to, say (100, 100) and show it afterwards, it should appear as standalone widget at 100,100 from TOP-LEFT corner of your SCREEN.

                  Btw: You should really use your layouts, not create them and then just throw your widgets (buttons) on your parent (LayoutExample window/widget) without actually putting them in a layout.

                  CASE 2

                  where is your this->show() located?! Cant tell right now...
                  The other 2 buttons are there because they are children of LayoutExample widget.... and you still show it with w.show() in your main()

                  Swati777999S Offline
                  Swati777999S Offline
                  Swati777999
                  wrote on last edited by
                  #41

                  @Pl45m4 said in Confusion between the usage of 'this' and 'parent':

                  @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                  CASE 2

                  where is your this->show() located?! Cant tell right now...

                  As mentioned in my previous reply, this->show() is located in layoutExample.cpp file.

                  “ In order to be irreplaceable, one must always be different” – Coco Chanel

                  Pl45m4P 1 Reply Last reply
                  0
                  • Swati777999S Swati777999

                    @Pl45m4 said in Confusion between the usage of 'this' and 'parent':

                    @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                    CASE 2

                    where is your this->show() located?! Cant tell right now...

                    As mentioned in my previous reply, this->show() is located in layoutExample.cpp file.

                    Pl45m4P Offline
                    Pl45m4P Offline
                    Pl45m4
                    wrote on last edited by Pl45m4
                    #42

                    @Swati777999

                    Shouldn't make any difference since this in your LayoutExample class and w in main are pretty much the same objects/instances. It's just the point when you show it. Using this->show at the end of c'tor shows the widget right after it is constructed. Then you do some stuff in main() and then w.show() would display it anyway.


                    If debugging is the process of removing software bugs, then programming must be the process of putting them in.

                    ~E. W. Dijkstra

                    Swati777999S 1 Reply Last reply
                    1
                    • Pl45m4P Pl45m4

                      @Swati777999

                      Shouldn't make any difference since this in your LayoutExample class and w in main are pretty much the same objects/instances. It's just the point when you show it. Using this->show at the end of c'tor shows the widget right after it is constructed. Then you do some stuff in main() and then w.show() would display it anyway.

                      Swati777999S Offline
                      Swati777999S Offline
                      Swati777999
                      wrote on last edited by
                      #43

                      @Pl45m4

                      My doubt is , even if I comment this->show() in layoutExample.cpp , the widgets in layoutExample.cpp still appear on the screen. How is it possible?

                      “ In order to be irreplaceable, one must always be different” – Coco Chanel

                      JKSHJ Pl45m4P 2 Replies Last reply
                      0
                      • Pl45m4P Pl45m4

                        @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                        In CASE-1 , why does quit button from main.cpp appear in the same window?

                        Because you've set w as parent of your quit button. So it appears in parent coodinates. If you remove the &w from your quit button's c'tor and still move it to, say (100, 100) and show it afterwards, it should appear as standalone widget at 100,100 from TOP-LEFT corner of your SCREEN.

                        Btw: You should really use your layouts, not create them and then just throw your widgets (buttons) on your parent (LayoutExample window/widget) without actually putting them in a layout.

                        CASE 2

                        where is your this->show() located?! Cant tell right now...
                        The other 2 buttons are there because they are children of LayoutExample widget.... and you still show it with w.show() in your main()

                        Swati777999S Offline
                        Swati777999S Offline
                        Swati777999
                        wrote on last edited by
                        #44

                        @Pl45m4 said in Confusion between the usage of 'this' and 'parent':

                        @Swati777999 said in Confusion between the usage of 'this' and 'parent':
                        Btw: You should really use your layouts, not create them and then just throw your widgets (buttons) on your parent (LayoutExample window/widget) without actually putting them in a layout.

                        I've used gridlayout for the widgets in layoutExample.cpp , you can check it below(as a part of layoutExample.cpp) but it seems that the layout has not been applied successfully.

                        LayoutExample::LayoutExample(QWidget *parent)
                            : QMainWindow(parent)
                        {
                            box = new QWidget(this);
                            button1=new QPushButton("Click Here",this);
                            button2 = new QPushButton("Sign up",this);
                            button1->move(200,200);
                            button2->move(100,100);
                            gridLay = new QGridLayout(this);
                            box->setFixedSize(50,50);
                        
                            gridLay->addWidget(box);
                            gridLay->addWidget(button1);
                            gridLay->addWidget(button2);
                        
                            this->setLayout(gridLay);
                        
                            this->show();
                        
                            //this->parentWidget()->setLayout(gridLay);
                        }
                        

                        “ In order to be irreplaceable, one must always be different” – Coco Chanel

                        JKSHJ 1 Reply Last reply
                        0
                        • Swati777999S Swati777999

                          @Pl45m4 said in Confusion between the usage of 'this' and 'parent':

                          @Swati777999 said in Confusion between the usage of 'this' and 'parent':
                          Btw: You should really use your layouts, not create them and then just throw your widgets (buttons) on your parent (LayoutExample window/widget) without actually putting them in a layout.

                          I've used gridlayout for the widgets in layoutExample.cpp , you can check it below(as a part of layoutExample.cpp) but it seems that the layout has not been applied successfully.

                          LayoutExample::LayoutExample(QWidget *parent)
                              : QMainWindow(parent)
                          {
                              box = new QWidget(this);
                              button1=new QPushButton("Click Here",this);
                              button2 = new QPushButton("Sign up",this);
                              button1->move(200,200);
                              button2->move(100,100);
                              gridLay = new QGridLayout(this);
                              box->setFixedSize(50,50);
                          
                              gridLay->addWidget(box);
                              gridLay->addWidget(button1);
                              gridLay->addWidget(button2);
                          
                              this->setLayout(gridLay);
                          
                              this->show();
                          
                              //this->parentWidget()->setLayout(gridLay);
                          }
                          
                          JKSHJ Offline
                          JKSHJ Offline
                          JKSH
                          Moderators
                          wrote on last edited by JKSH
                          #45

                          @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                          My doubt here is ; in CASE-2, why should these buttons; Sign up and Click Here appear as this->show() is commented?

                          In CASE-1 , why does quit button from main.cpp appear in the same window?

                          Please explain the reason.

                          I think you've got CASE-1 and CASE-2 mixed up. quit will show if this->show() is commented.

                          The reason is this: When you call show() on a widget, it also automatically calls show() on all of the widget's children.

                          • When you show w before setting it as the parent of quit, then quit won't be shown. You must call quit.show() manually.
                          • When you show w after setting it as the parent of quit, then quit will be automatically shown.

                          But more importantly: You don't need to spend time worrying about things like this. If you just put ALL of your child widgets inside layouts, then you won't encounter these strange behaviours!

                          I've used gridlayout for the widgets... but it seems that the layout has not been applied successfully.

                          Look, both @SimonSchroeder and I have told you already: You must specify the row and column when you call QGridLayout::addWidget(): https://doc.qt.io/qt-5/qgridlayout.html#addWidget-1

                          It irritates us when you ignore our advice and then repeat the same issue.

                          Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                          Swati777999S 1 Reply Last reply
                          1
                          • JKSHJ JKSH

                            @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                            My doubt here is ; in CASE-2, why should these buttons; Sign up and Click Here appear as this->show() is commented?

                            In CASE-1 , why does quit button from main.cpp appear in the same window?

                            Please explain the reason.

                            I think you've got CASE-1 and CASE-2 mixed up. quit will show if this->show() is commented.

                            The reason is this: When you call show() on a widget, it also automatically calls show() on all of the widget's children.

                            • When you show w before setting it as the parent of quit, then quit won't be shown. You must call quit.show() manually.
                            • When you show w after setting it as the parent of quit, then quit will be automatically shown.

                            But more importantly: You don't need to spend time worrying about things like this. If you just put ALL of your child widgets inside layouts, then you won't encounter these strange behaviours!

                            I've used gridlayout for the widgets... but it seems that the layout has not been applied successfully.

                            Look, both @SimonSchroeder and I have told you already: You must specify the row and column when you call QGridLayout::addWidget(): https://doc.qt.io/qt-5/qgridlayout.html#addWidget-1

                            It irritates us when you ignore our advice and then repeat the same issue.

                            Swati777999S Offline
                            Swati777999S Offline
                            Swati777999
                            wrote on last edited by
                            #46

                            @JKSH

                            Yes, I remember your advice of giving a dimension to my layout to make it appear on the screen, I was mistakenly putting row,column parameters while creating gridLay as a result of which I was getting errors repeatedly but now , I understood the concept.

                            gridLay->addWidget(button1,100,120,Qt::Alignment=0x0020);

                            The third argument gives me an error. How should the value of alignment be used?
                            Qt::Alignment=0x0020

                            “ In order to be irreplaceable, one must always be different” – Coco Chanel

                            J.HilkJ 1 Reply Last reply
                            0
                            • Swati777999S Swati777999

                              @JKSH

                              Yes, I remember your advice of giving a dimension to my layout to make it appear on the screen, I was mistakenly putting row,column parameters while creating gridLay as a result of which I was getting errors repeatedly but now , I understood the concept.

                              gridLay->addWidget(button1,100,120,Qt::Alignment=0x0020);

                              The third argument gives me an error. How should the value of alignment be used?
                              Qt::Alignment=0x0020

                              J.HilkJ Offline
                              J.HilkJ Offline
                              J.Hilk
                              Moderators
                              wrote on last edited by
                              #47

                              @Swati777999

                              gridLay->addWidget(button1,100,120,Qt::Alignment=0x0020);
                              

                              100,120 does not mean the pixels on your screen, but row/column 100/120

                              try placing your first widget on column/row 0 and use the actual enum not the integer value as 4th paramter

                              gridLay->addWidget(button1,0,0,Qt::AlignTop);
                              

                              Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                              Q: What's that?
                              A: It's blue light.
                              Q: What does it do?
                              A: It turns blue.

                              Swati777999S 1 Reply Last reply
                              1
                              • J.HilkJ J.Hilk

                                @Swati777999

                                gridLay->addWidget(button1,100,120,Qt::Alignment=0x0020);
                                

                                100,120 does not mean the pixels on your screen, but row/column 100/120

                                try placing your first widget on column/row 0 and use the actual enum not the integer value as 4th paramter

                                gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                
                                Swati777999S Offline
                                Swati777999S Offline
                                Swati777999
                                wrote on last edited by
                                #48

                                @J-Hilk

                                After modifying the existing code, gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                I can't find any change in my display. :(

                                “ In order to be irreplaceable, one must always be different” – Coco Chanel

                                1 Reply Last reply
                                0
                                • Swati777999S Swati777999

                                  @Pl45m4

                                  My doubt is , even if I comment this->show() in layoutExample.cpp , the widgets in layoutExample.cpp still appear on the screen. How is it possible?

                                  JKSHJ Offline
                                  JKSHJ Offline
                                  JKSH
                                  Moderators
                                  wrote on last edited by JKSH
                                  #49

                                  @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                  My doubt is , even if I comment this->show() in layoutExample.cpp , the widgets in layoutExample.cpp still appear on the screen. How is it possible?

                                  Because you called w.show().

                                  After modifying the existing code, gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                  I can't find any change in my display. :(

                                  First: Instead of QMainWindow, make your widget inherit QWidget. This makes things simpler.

                                  Second: You only put one button in the layout. You should put ALL buttons in the layout. Remember to use different rows/columns for each button.

                                  Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                                  Swati777999S 2 Replies Last reply
                                  2
                                  • JKSHJ JKSH

                                    @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                    My doubt is , even if I comment this->show() in layoutExample.cpp , the widgets in layoutExample.cpp still appear on the screen. How is it possible?

                                    Because you called w.show().

                                    After modifying the existing code, gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                    I can't find any change in my display. :(

                                    First: Instead of QMainWindow, make your widget inherit QWidget. This makes things simpler.

                                    Second: You only put one button in the layout. You should put ALL buttons in the layout. Remember to use different rows/columns for each button.

                                    Swati777999S Offline
                                    Swati777999S Offline
                                    Swati777999
                                    wrote on last edited by
                                    #50

                                    @JKSH

                                    This is the LayoutExample.cpp

                                    LayoutExample::LayoutExample(QWidget *parent)
                                        : QMainWindow(parent)
                                    {
                                    ............
                                    }
                                    

                                    In place of QMainWindow, if I put QWidget, it gives an error. For example:

                                    LayoutExample::LayoutExample(QWidget *parent)
                                        : QWidget(parent)
                                    {
                                    ............
                                    }
                                    

                                    “ In order to be irreplaceable, one must always be different” – Coco Chanel

                                    JKSHJ 1 Reply Last reply
                                    0
                                    • JKSHJ JKSH

                                      @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                      My doubt is , even if I comment this->show() in layoutExample.cpp , the widgets in layoutExample.cpp still appear on the screen. How is it possible?

                                      Because you called w.show().

                                      After modifying the existing code, gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                      I can't find any change in my display. :(

                                      First: Instead of QMainWindow, make your widget inherit QWidget. This makes things simpler.

                                      Second: You only put one button in the layout. You should put ALL buttons in the layout. Remember to use different rows/columns for each button.

                                      Swati777999S Offline
                                      Swati777999S Offline
                                      Swati777999
                                      wrote on last edited by
                                      #51

                                      @JKSH said in Confusion between the usage of 'this' and 'parent':

                                      @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                      My doubt is , even if I comment this->show() in layoutExample.cpp , the widgets in layoutExample.cpp still appear on the screen. How is it possible?

                                      Because you called w.show().

                                      After modifying the existing code, gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                      I can't find any change in my display. :(

                                      First: Instead of QMainWindow, make your widget inherit QWidget. This makes things simpler.

                                      Second: You only put one button in the layout. You should put ALL buttons in the layout. Remember to use different rows/columns for each button.
                                      This is the complete code, please refer to it.

                                      LayoutExample.cpp

                                      LayoutExample::LayoutExample(QWidget *parent)
                                          : QMainWindow(parent)
                                      
                                      {   gridLay = new QGridLayout(this);
                                          box = new QWidget(this);
                                          button1=new QPushButton("Click Here",this);
                                          button2 = new QPushButton("Sign up",this);
                                          button1->move(200,200);
                                          button2->move(100,100);
                                      
                                          gridLay->addWidget(box,60,60);
                                          gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                          gridLay->addWidget(button2,50,100,Qt::AlignBottom);
                                      
                                          this->setLayout(gridLay);
                                          this->show();
                                      
                                      
                                      }
                                      
                                      LayoutExample::~LayoutExample()
                                      {
                                      }
                                      

                                      “ In order to be irreplaceable, one must always be different” – Coco Chanel

                                      1 Reply Last reply
                                      0
                                      • Swati777999S Swati777999

                                        @JKSH

                                        This is the LayoutExample.cpp

                                        LayoutExample::LayoutExample(QWidget *parent)
                                            : QMainWindow(parent)
                                        {
                                        ............
                                        }
                                        

                                        In place of QMainWindow, if I put QWidget, it gives an error. For example:

                                        LayoutExample::LayoutExample(QWidget *parent)
                                            : QWidget(parent)
                                        {
                                        ............
                                        }
                                        
                                        JKSHJ Offline
                                        JKSHJ Offline
                                        JKSH
                                        Moderators
                                        wrote on last edited by
                                        #52

                                        @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                        In place of QMainWindow, if I put QWidget, it gives an error.

                                        You must update your .h file too.

                                        gridLay->addWidget(box,60,60);
                                        gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                        gridLay->addWidget(button2,50,100,Qt::AlignBottom);
                                        

                                        You want to specify row/column number. Not pixel number.

                                        I suggest you use a QVBoxLayout for now. It's simpler than QGridLayout.

                                        Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                                        Swati777999S 1 Reply Last reply
                                        2
                                        • JKSHJ JKSH

                                          @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                          In place of QMainWindow, if I put QWidget, it gives an error.

                                          You must update your .h file too.

                                          gridLay->addWidget(box,60,60);
                                          gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                          gridLay->addWidget(button2,50,100,Qt::AlignBottom);
                                          

                                          You want to specify row/column number. Not pixel number.

                                          I suggest you use a QVBoxLayout for now. It's simpler than QGridLayout.

                                          Swati777999S Offline
                                          Swati777999S Offline
                                          Swati777999
                                          wrote on last edited by
                                          #53

                                          @JKSH said in Confusion between the usage of 'this' and 'parent':

                                          @Swati777999 said in Confusion between the usage of 'this' and 'parent':

                                          You must update your .h file too.
                                          Done! It works now!
                                          Layout_Example4.PNG

                                          gridLay->addWidget(box,60,60);
                                          gridLay->addWidget(button1,0,0,Qt::AlignTop);
                                          gridLay->addWidget(button2,50,100,Qt::AlignBottom);
                                          

                                          You want to specify row/column number. Not pixel number.
                                          Noted!

                                          I suggest you use a QVBoxLayout for now. It's simpler than QGridLayout.
                                          Okay

                                          “ In order to be irreplaceable, one must always be different” – Coco Chanel

                                          1 Reply Last reply
                                          1

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