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Forum Update on Monday, May 27th 2025

QUndoStack across 2 cpps? QTreeView and QGraphicsScene

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qundostackqundocommandc++qtqtreeviewqgraphicsscene
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  • SGaistS Offline
    SGaistS Offline
    SGaist
    Lifetime Qt Champion
    wrote on last edited by
    #2

    Hi,

    The most simple would be to share the model between the graphics view and the tree view.

    That way you can manage the entries in your command rather than as an external event.

    Interested in AI ? www.idiap.ch
    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

    S 1 Reply Last reply
    2
    • SGaistS SGaist

      Hi,

      The most simple would be to share the model between the graphics view and the tree view.

      That way you can manage the entries in your command rather than as an external event.

      S Offline
      S Offline
      StudentScripter
      wrote on last edited by StudentScripter
      #3

      @SGaist The problem is i still have to perform many actions in the graphicsscene destinating from the qtreeview and vice verca. Therefore i already have the graphicsscene included in my qtreeview class. For example when i select the qstandarditem an corresponding graphicsitem gets selected and vice verca. When i click on the checkbox of the qtsandarditem the corresponding graphcisitems gets hidden etc. you get the idea.

      As i know including the qtreeview class inside the graphicsscnene.cpp would lead to circular dependency, i would like to avoid that. But may you could further elaborate how you would do it? Maybe im just to stuck in my progress to see good alternative ways.

      class ViewLayerList : public QTreeView
      {
          Q_OBJECT
      public:
          explicit ViewLayerList(CustomGraphicsScene *scene, QWidget *parent = nullptr);
      

      Also before i forget it: Thank you very much. <3

      JonBJ 1 Reply Last reply
      0
      • S StudentScripter

        @SGaist The problem is i still have to perform many actions in the graphicsscene destinating from the qtreeview and vice verca. Therefore i already have the graphicsscene included in my qtreeview class. For example when i select the qstandarditem an corresponding graphicsitem gets selected and vice verca. When i click on the checkbox of the qtsandarditem the corresponding graphcisitems gets hidden etc. you get the idea.

        As i know including the qtreeview class inside the graphicsscnene.cpp would lead to circular dependency, i would like to avoid that. But may you could further elaborate how you would do it? Maybe im just to stuck in my progress to see good alternative ways.

        class ViewLayerList : public QTreeView
        {
            Q_OBJECT
        public:
            explicit ViewLayerList(CustomGraphicsScene *scene, QWidget *parent = nullptr);
        

        Also before i forget it: Thank you very much. <3

        JonBJ Offline
        JonBJ Offline
        JonB
        wrote on last edited by JonB
        #4

        @StudentScripter
        It seems to me you have two possible general approaches:

        • Use signals & slots to communicate between the tree view and the graphics scene. This can alleviate the need for each side to know too much about the other side. But be careful not to get into an "infinite loop", where each side "ping pongs" signals between themselves for some change.

        • As @SGaist says, create a common model and share the model between both sides. For example, QStandardItem is part of a QStandardItemModel. You can already have multiple views (e.g. QTreeView) attached to the same model, make it so (some wrapper around) the QGraphicsScene shares that model with your one QTreeView. All your operations, like selecting or clicking a checkbox, should be implemented in the model, not the view or scene. Then that emits signals like dataChanged() or selectionChanged() in response to your actions and both views get notified about it and react in their own ways. The model code can be kept in its own/class/module/file, that is included into both the tree view & graphics scene classes, they should not need to see each other directly. This would be my inclination.

        S JonBJ 2 Replies Last reply
        0
        • JonBJ JonB

          @StudentScripter
          It seems to me you have two possible general approaches:

          • Use signals & slots to communicate between the tree view and the graphics scene. This can alleviate the need for each side to know too much about the other side. But be careful not to get into an "infinite loop", where each side "ping pongs" signals between themselves for some change.

          • As @SGaist says, create a common model and share the model between both sides. For example, QStandardItem is part of a QStandardItemModel. You can already have multiple views (e.g. QTreeView) attached to the same model, make it so (some wrapper around) the QGraphicsScene shares that model with your one QTreeView. All your operations, like selecting or clicking a checkbox, should be implemented in the model, not the view or scene. Then that emits signals like dataChanged() or selectionChanged() in response to your actions and both views get notified about it and react in their own ways. The model code can be kept in its own/class/module/file, that is included into both the tree view & graphics scene classes, they should not need to see each other directly. This would be my inclination.

          S Offline
          S Offline
          StudentScripter
          wrote on last edited by
          #5

          @JonB Ok but im using delegates. How can i get within the model if the position of an checkbox was clicked when the delegate isn't even created?

          So i click at the position where i see the checkbox but in reality there is no real checkbox but only the paint event of the delegate. The actual checkbox is only created on double click.

          Couldn't i just use a singleton class to exchange the model?

          JonBJ 1 Reply Last reply
          0
          • S StudentScripter

            @JonB Ok but im using delegates. How can i get within the model if the position of an checkbox was clicked when the delegate isn't even created?

            So i click at the position where i see the checkbox but in reality there is no real checkbox but only the paint event of the delegate. The actual checkbox is only created on double click.

            Couldn't i just use a singleton class to exchange the model?

            JonBJ Offline
            JonBJ Offline
            JonB
            wrote on last edited by JonB
            #6

            @StudentScripter said in QUndoStack across 2 cpps? QTreeView and QGraphicsScene:

            but in reality there is no real checkbox but only the paint event of the delegate

            You have to connect that to a model. Else you have nowhere to store the state for things which just happen in the UI. Look at how, say, checkbox state is linked to Qt::CheckState QStandardItem::checkState() const or QVariant QAbstractItemModel::data(const QModelIndex &index, int role = Qt::DisplayRole) const with enum Qt::ItemDataRole set to Qt::CheckStateRole. And the delegate deals with this. And you can have a common model which has some aspects reflected/not reflected in a tree view and other aspects in a graphics scene.

            I have no idea what "a singleton class to exchange the model" is about, but it's a detail compared to the overall concept.

            S 1 Reply Last reply
            0
            • JonBJ JonB

              @StudentScripter said in QUndoStack across 2 cpps? QTreeView and QGraphicsScene:

              but in reality there is no real checkbox but only the paint event of the delegate

              You have to connect that to a model. Else you have nowhere to store the state for things which just happen in the UI. Look at how, say, checkbox state is linked to Qt::CheckState QStandardItem::checkState() const or QVariant QAbstractItemModel::data(const QModelIndex &index, int role = Qt::DisplayRole) const with enum Qt::ItemDataRole set to Qt::CheckStateRole. And the delegate deals with this. And you can have a common model which has some aspects reflected/not reflected in a tree view and other aspects in a graphics scene.

              I have no idea what "a singleton class to exchange the model" is about, but it's a detail compared to the overall concept.

              S Offline
              S Offline
              StudentScripter
              wrote on last edited by
              #7

              @JonB Well what do you mean with common model at all?

              I have a QStandardItemModel and i do already set the checkstate. However the problem i have is that the checkstate has to be set when clicking at the standard item at a certain position. Im currently doing this in the qtreeviews mousepressevent:

              void ViewLayerList::mousePressEvent(QMouseEvent *event)
              {  
              
              
                  //Bekommt den Index welcher gerade unter der Mouse Position ist
                  indexAtMouse = indexAt(event->position().toPoint());
              
                  
                  // Zugriff auf das SelectionModel, um ausgewählte Items zu erhalten
                  QItemSelectionModel *selectionModel = this->selectionModel();
              
                  // Überprüfen, ob ein SelectionModel vorhanden ist
                  if (selectionModel) {
                      selectedIndexes = selectionModel->selectedIndexes();
                  }
                  
                  int columnWidth = this->columnWidth(0);
                  int ClickPosX = event->position().x();
              
              
                 
                  if(ClickPosX >= columnWidth-40 && ClickPosX <= columnWidth -15){
                      if(selectedIndexes.count()>1){
                          for (const QModelIndex &index : selectedIndexes) {
                              bool value = index.data(Qt::CheckStateRole).toBool();
                              model->setData(index, !value, Qt::CheckStateRole);
                         } 
                    }
              }
              
              }
              
              SGaistS 1 Reply Last reply
              0
              • S StudentScripter

                @JonB Well what do you mean with common model at all?

                I have a QStandardItemModel and i do already set the checkstate. However the problem i have is that the checkstate has to be set when clicking at the standard item at a certain position. Im currently doing this in the qtreeviews mousepressevent:

                void ViewLayerList::mousePressEvent(QMouseEvent *event)
                {  
                
                
                    //Bekommt den Index welcher gerade unter der Mouse Position ist
                    indexAtMouse = indexAt(event->position().toPoint());
                
                    
                    // Zugriff auf das SelectionModel, um ausgewählte Items zu erhalten
                    QItemSelectionModel *selectionModel = this->selectionModel();
                
                    // Überprüfen, ob ein SelectionModel vorhanden ist
                    if (selectionModel) {
                        selectedIndexes = selectionModel->selectedIndexes();
                    }
                    
                    int columnWidth = this->columnWidth(0);
                    int ClickPosX = event->position().x();
                
                
                   
                    if(ClickPosX >= columnWidth-40 && ClickPosX <= columnWidth -15){
                        if(selectedIndexes.count()>1){
                            for (const QModelIndex &index : selectedIndexes) {
                                bool value = index.data(Qt::CheckStateRole).toBool();
                                model->setData(index, !value, Qt::CheckStateRole);
                           } 
                      }
                }
                
                }
                
                SGaistS Offline
                SGaistS Offline
                SGaist
                Lifetime Qt Champion
                wrote on last edited by
                #8

                That's the role of QStyledItemDelegate::editorEvent.

                Interested in AI ? www.idiap.ch
                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                S 1 Reply Last reply
                0
                • SGaistS SGaist

                  That's the role of QStyledItemDelegate::editorEvent.

                  S Offline
                  S Offline
                  StudentScripter
                  wrote on last edited by
                  #9

                  @SGaist But the editor event is only triggert when the delegate is activated/created right? When the editor isn't currently active this wont work. I want it to set the checked even when the editor at this index isn't created/open.

                  JonBJ SGaistS 2 Replies Last reply
                  0
                  • S StudentScripter

                    @SGaist But the editor event is only triggert when the delegate is activated/created right? When the editor isn't currently active this wont work. I want it to set the checked even when the editor at this index isn't created/open.

                    JonBJ Offline
                    JonBJ Offline
                    JonB
                    wrote on last edited by JonB
                    #10

                    @StudentScripter said in QUndoStack across 2 cpps? QTreeView and QGraphicsScene:

                    I want it to set the checked even when the editor at this index isn't created/open.

                    I don't understand this. Why can't you store that information in a model and when the delegate is shown the state is picked up from there and displayed then? Not store the state in a delegate instance which does not currently exist.

                    But I don't understand your situation, I don't know where a graphics scene comes into it, I don't know what it has to do with the title of QUndoStack across multiple .cpp files. And I doubt I will :) So will try to leave it to you/others who understand better.

                    S 1 Reply Last reply
                    0
                    • S StudentScripter

                      @SGaist But the editor event is only triggert when the delegate is activated/created right? When the editor isn't currently active this wont work. I want it to set the checked even when the editor at this index isn't created/open.

                      SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #11

                      @StudentScripter No, it will also be called for other interactions. See here.

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                      1 Reply Last reply
                      0
                      • JonBJ JonB

                        @StudentScripter said in QUndoStack across 2 cpps? QTreeView and QGraphicsScene:

                        I want it to set the checked even when the editor at this index isn't created/open.

                        I don't understand this. Why can't you store that information in a model and when the delegate is shown the state is picked up from there and displayed then? Not store the state in a delegate instance which does not currently exist.

                        But I don't understand your situation, I don't know where a graphics scene comes into it, I don't know what it has to do with the title of QUndoStack across multiple .cpp files. And I doubt I will :) So will try to leave it to you/others who understand better.

                        S Offline
                        S Offline
                        StudentScripter
                        wrote on last edited by StudentScripter
                        #12

                        @JonB Haha no problem. Your answers where quite helpful still. And i guess i will adapt a few things the way you suggested. :D Will try to give the scene access to the model.

                        @SGaist So even when the delegate isn't active in the standarditem clicked on it will still receive those clicks?

                        SGaistS 1 Reply Last reply
                        0
                        • S StudentScripter

                          @JonB Haha no problem. Your answers where quite helpful still. And i guess i will adapt a few things the way you suggested. :D Will try to give the scene access to the model.

                          @SGaist So even when the delegate isn't active in the standarditem clicked on it will still receive those clicks?

                          SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #13

                          @StudentScripter the delegate is always active once you set it. Or did you mean the editor ? If so, then yes, the events will be sent to the delegate.

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                          S 1 Reply Last reply
                          1
                          • SGaistS SGaist

                            @StudentScripter the delegate is always active once you set it. Or did you mean the editor ? If so, then yes, the events will be sent to the delegate.

                            S Offline
                            S Offline
                            StudentScripter
                            wrote on last edited by StudentScripter
                            #14

                            @SGaist Yeah i probably mean the editor cause my delegate is visible trough its paint event even if the editor is closed, right?

                            Now i click on one position of my delegate (the editor is still closed/or should stay closed) but i still want to change the Qt::CheckStateRole of that indexes delegate.

                            Is this understandable? Thanks for your help and time too. Can't say that often enough.

                            Also could i just add a setter function in my graphicsscene and set the model from the treeview? As said i have access from the treeview to the model object and the graphicsscene. Like this:

                            #include "ViewLayerList.h"
                            #include <QHBoxLayout>
                            #include <QCheckBox>
                            #include <QLabel>
                            #include "ViewLayerDropIndicatorStyle.h"
                            #include <QMouseEvent>
                            #include "resizablepixmapitem.h"
                            #include <QHeaderView>
                            #include <QPushButton>
                            
                            #include <QTimer>
                            #include <QApplication>
                            #include <QDrag>
                            #include <QCursor>
                            #include <QMimeData>
                            
                            #include <QApplication>
                            #include <QFile>
                            #include <QDataStream>
                            
                            #include <QJsonDocument>
                            #include <QJsonObject>
                            #include <QJsonArray>
                            
                            #include <QUndoCommand>
                            #include "CommandManager.h"
                            
                            
                            
                            
                            
                            ViewLayerList::ViewLayerList(CustomGraphicsScene *scene, QWidget *parent)
                                : QTreeView{parent}, scene_durchgereicht(scene)
                            {
                            
                                            
                            
                            
                            
                            
                            
                             setStyle(new ViewLayerDropIndicatorStyle(style()));
                            
                            
                             // Ändern Sie den Abstand zwischen den Items und der vertikalen Scrollbar
                                setViewportMargins(0, 0, 50, 0); // Passen Sie den rechten Rand (20) an Ihre Anforderungen an
                                
                            //Versteckt die sinnlose Kopfzeile
                                setHeaderHidden(true);
                                setRootIsDecorated(true);
                                setMouseTracking(true);
                            
                            
                            
                            
                            
                            
                            
                            mydelegate = new ViewLayerItemDelegate(this);
                            
                            
                            
                            model = new ViewLayerStandartItemModel(0,1,this);
                            
                            
                            scene_durchgereicht->setModel(model); //Dieses exakte model
                            }
                            
                            S 1 Reply Last reply
                            0
                            • S StudentScripter

                              @SGaist Yeah i probably mean the editor cause my delegate is visible trough its paint event even if the editor is closed, right?

                              Now i click on one position of my delegate (the editor is still closed/or should stay closed) but i still want to change the Qt::CheckStateRole of that indexes delegate.

                              Is this understandable? Thanks for your help and time too. Can't say that often enough.

                              Also could i just add a setter function in my graphicsscene and set the model from the treeview? As said i have access from the treeview to the model object and the graphicsscene. Like this:

                              #include "ViewLayerList.h"
                              #include <QHBoxLayout>
                              #include <QCheckBox>
                              #include <QLabel>
                              #include "ViewLayerDropIndicatorStyle.h"
                              #include <QMouseEvent>
                              #include "resizablepixmapitem.h"
                              #include <QHeaderView>
                              #include <QPushButton>
                              
                              #include <QTimer>
                              #include <QApplication>
                              #include <QDrag>
                              #include <QCursor>
                              #include <QMimeData>
                              
                              #include <QApplication>
                              #include <QFile>
                              #include <QDataStream>
                              
                              #include <QJsonDocument>
                              #include <QJsonObject>
                              #include <QJsonArray>
                              
                              #include <QUndoCommand>
                              #include "CommandManager.h"
                              
                              
                              
                              
                              
                              ViewLayerList::ViewLayerList(CustomGraphicsScene *scene, QWidget *parent)
                                  : QTreeView{parent}, scene_durchgereicht(scene)
                              {
                              
                                              
                              
                              
                              
                              
                              
                               setStyle(new ViewLayerDropIndicatorStyle(style()));
                              
                              
                               // Ändern Sie den Abstand zwischen den Items und der vertikalen Scrollbar
                                  setViewportMargins(0, 0, 50, 0); // Passen Sie den rechten Rand (20) an Ihre Anforderungen an
                                  
                              //Versteckt die sinnlose Kopfzeile
                                  setHeaderHidden(true);
                                  setRootIsDecorated(true);
                                  setMouseTracking(true);
                              
                              
                              
                              
                              
                              
                              
                              mydelegate = new ViewLayerItemDelegate(this);
                              
                              
                              
                              model = new ViewLayerStandartItemModel(0,1,this);
                              
                              
                              scene_durchgereicht->setModel(model); //Dieses exakte model
                              }
                              
                              S Offline
                              S Offline
                              StudentScripter
                              wrote on last edited by
                              #15

                              bumping this

                              SGaistS 1 Reply Last reply
                              0
                              • S StudentScripter

                                bumping this

                                SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #16

                                @StudentScripter your tree view has no reason to be doing that setup with the scene. They share a model, they don't need to know about each other.

                                As for the delegate, your goal is clear, and again, the editorEvent is what you want to use to implement the behavior you want.

                                Interested in AI ? www.idiap.ch
                                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                S 1 Reply Last reply
                                1
                                • SGaistS SGaist

                                  @StudentScripter your tree view has no reason to be doing that setup with the scene. They share a model, they don't need to know about each other.

                                  As for the delegate, your goal is clear, and again, the editorEvent is what you want to use to implement the behavior you want.

                                  S Offline
                                  S Offline
                                  StudentScripter
                                  wrote on last edited by
                                  #17

                                  @SGaist Well but as i understand it with

                                  model = new ViewLayerStandartItemModel(0,1,this);
                                  

                                  im creating a new instance of this class, a new object. So in order to have access to the same model i have to pass the object i create in the treeview trough to the scene.
                                  Is this a mistake? How should i do it instead?

                                  SGaistS 1 Reply Last reply
                                  0
                                  • S StudentScripter

                                    @SGaist Well but as i understand it with

                                    model = new ViewLayerStandartItemModel(0,1,this);
                                    

                                    im creating a new instance of this class, a new object. So in order to have access to the same model i have to pass the object i create in the treeview trough to the scene.
                                    Is this a mistake? How should i do it instead?

                                    SGaistS Offline
                                    SGaistS Offline
                                    SGaist
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #18

                                    @StudentScripter you should create the model in the class that manages the ViewLayerList object and set it on both objects there. In the absolute, with the code you show, ViewLayerList is not even needed unless there are some additional function you are implementing. If not, then just use QTreeView directly and configure it in the class managing it.

                                    Interested in AI ? www.idiap.ch
                                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                    S 1 Reply Last reply
                                    1
                                    • SGaistS SGaist

                                      @StudentScripter you should create the model in the class that manages the ViewLayerList object and set it on both objects there. In the absolute, with the code you show, ViewLayerList is not even needed unless there are some additional function you are implementing. If not, then just use QTreeView directly and configure it in the class managing it.

                                      S Offline
                                      S Offline
                                      StudentScripter
                                      wrote on last edited by
                                      #19

                                      @SGaist Yes im implementing additional functions in the qtreeview/ViewLayerList, thats why i subclassed it. Im creating the model object directly in ViewLayerLists constructor, cause i use that model mostly in this cpp.

                                      So i guess my approach with giving the model from there to the scene is okish?

                                      SGaistS 1 Reply Last reply
                                      0
                                      • S StudentScripter

                                        @SGaist Yes im implementing additional functions in the qtreeview/ViewLayerList, thats why i subclassed it. Im creating the model object directly in ViewLayerLists constructor, cause i use that model mostly in this cpp.

                                        So i guess my approach with giving the model from there to the scene is okish?

                                        SGaistS Offline
                                        SGaistS Offline
                                        SGaist
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #20

                                        @StudentScripter no, it makes that class know another one just for the purpose of sharing the model. That's tight coupling for the bad reasons.

                                        Interested in AI ? www.idiap.ch
                                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                        1 Reply Last reply
                                        1
                                        • JonBJ JonB

                                          @StudentScripter
                                          It seems to me you have two possible general approaches:

                                          • Use signals & slots to communicate between the tree view and the graphics scene. This can alleviate the need for each side to know too much about the other side. But be careful not to get into an "infinite loop", where each side "ping pongs" signals between themselves for some change.

                                          • As @SGaist says, create a common model and share the model between both sides. For example, QStandardItem is part of a QStandardItemModel. You can already have multiple views (e.g. QTreeView) attached to the same model, make it so (some wrapper around) the QGraphicsScene shares that model with your one QTreeView. All your operations, like selecting or clicking a checkbox, should be implemented in the model, not the view or scene. Then that emits signals like dataChanged() or selectionChanged() in response to your actions and both views get notified about it and react in their own ways. The model code can be kept in its own/class/module/file, that is included into both the tree view & graphics scene classes, they should not need to see each other directly. This would be my inclination.

                                          JonBJ Offline
                                          JonBJ Offline
                                          JonB
                                          wrote on last edited by
                                          #21

                                          @JonB said in QUndoStack across 2 cpps? QTreeView and QGraphicsScene:

                                          The model code can be kept in its own/class/module/file, that is included into both the tree view & graphics scene classes, they should not need to see each other directly. This would be my inclination.

                                          S 1 Reply Last reply
                                          1

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