QUndoStack across 2 cpps? QTreeView and QGraphicsScene

[StudentScripter]

So im trying to get started with QUndo Framework however im quite stuck in this situation. Let me explain the situation:

I have an mainwindow from which i trigger the undo/redo funktions in my scene:

void CustomGraphicsScene::undo()
{
    undoStack->undo();
}

void CustomGraphicsScene::redo()
{
    undoStack->redo();
}
          

I've created a new cpp to house my add and remove functions:

#include "CommandManager.h"

AddCommand::AddCommand(QGraphicsItem *SceneItem, QGraphicsScene *scene, QStandardItem *ListItem) :
    item_durchgereicht(SceneItem), scene_durchgereicht(scene), listItem_durchgereicht(ListItem)
{
    
}


void AddCommand::undo()
{
    if (item_durchgereicht){
        scene_durchgereicht->removeItem(item_durchgereicht);
    }  
}

void AddCommand::redo()
{
    if(item_durchgereicht){
        scene_durchgereicht->addItem(item_durchgereicht);
    }
}

I add the items in my scene to the stack however here is the point where it gets tricky:

void CustomGraphicsScene::dropEvent(QGraphicsSceneDragDropEvent *event)
{
    if(event->mimeData()->property("Key").canConvert(QMetaType(QMetaType::Int))){

        int key = event->mimeData()->property("Key").toInt();
        
        switch(key){
        
            case 10: {
            clearSelection();
            ResizablePixmapItem * pixItem = new ResizablePixmapItem(QPixmap(":/resource/quick.png"));
            pixItem->setRect(0,0,100,100);
            pixItem->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemSendsScenePositionChanges);
            
  
            



            //Erhöht den Counter für jedes gedroppete Item
            SceneItemCounter++;
            pixItem->setSceneID(SceneItemCounter);
            qDebug() << "SceneID: " << pixItem->getSceneID();
            
            
            addCommand = new AddCommand(pixItem, this, nullptr);
            undoStack->push(addCommand);    
            //addItem(pixItem);
            pixItem->setPos(event->scenePos() - QPointF(pixItem->boundingRect().width()/2, pixItem->boundingRect().height()/2));
            pixItem->setSelected(true);
            
           
            emit SendNewItemWasAddedtoScene(pixItem);
            emit SendItemsInSceneSelected();  
            }
            break;

You see everytime i add an entry trough drop to the scene i send an signal to my Qtreeview/ViewLayerList with the item that was added (emit SendNewItemWasAddedtoScene(pixItem);). I do this cause for every item added to the scene i add an QStandardItem to the QTreeView mirroring the name etc. of the graphicsitem. I have access to the scene from the treeview to the scene but not from the scene to the treeview directly cause this would cause circular dependency which wouldn't be good, right? But now if i call undo/redo of an graphicsitem the corresponding qstandarditem should be removed/added too without an seperate undostack entry. How could i do that?

Here is how i add that entry when receiving the signal from the graphicsscene for the drop of the item:

void ViewLayerList::ReceiveNewItemWasAddedtoScene(QGraphicsItem *GraphicsItem)
{
qDebug() << "Item added: " << GraphicsItem;
if(model) {
    // Erstellen Sie ein neues QStandardItem
    QStandardItem *ListEntryItem = new QStandardItem();
    model->appendRow(ListEntryItem);
    
    
       //Casten ob es ein ResizablePixmapItem ist um den Namen zu retrieven
    ResizablePixmapItem* resizableItem = dynamic_cast<ResizablePixmapItem*>(GraphicsItem);
    if (resizableItem) { 
    
    
    // Holen Sie sich den Index des neu hinzugefügten Elements
    QModelIndex index = model->indexFromItem(ListEntryItem);
    
        // Setzen Sie die Daten für das neue Element
    model->setData(index, false, ViewLayerStandartItemModel::CanHaveChildrenRole); // Dieses Element kann keine Kinder haben
    
    
   

    QPixmap ItemIconPixmap = resizableItem->getPixmap(); // Ersetzen Sie "path/to/your/pixmap.png" durch den Pfad zu Ihrer Bilddatei
        QPixmap SCItemIconPixmap = ItemIconPixmap.scaled(32,32, Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);
    int xOffset = (SCItemIconPixmap.width() - 32) / 2;
    int yOffset = (SCItemIconPixmap.height() - 32) / 2;
    
   
    
    QPixmap finalPixmap = SCItemIconPixmap.copy(xOffset, yOffset, 32, 32);
    model->setData(index, finalPixmap, Qt::DecorationRole);


   QString ItemName = resizableItem->getControlName();
   model->setData(index, ItemName, Qt::EditRole);




    
    
    //Setzt für das Listenitem als ID den selben Integer Wert wie für das dazugehörige GraphicsItem aus der Scene
    qDebug() << "SceneID is: " << resizableItem->getSceneID();
    model->setData(index, resizableItem->getSceneID(), ViewLayerStandartItemModel::ListIDRole);
    
    
}
}

}

Here is a picture that visualizes that, everytime i add an item to the scene i add one to the qtreeview:
I know this is a little complex but im really stuck here. Thanks for all hints and help i really appreciate that. Have a nice day y'all. :D

[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.

[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

[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.

[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?

[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.

[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);
           } 
      }
}

}

[SGaist]

That's the role of QStyledItemDelegate::editorEvent.

[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.

[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.

[SGaist]

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

[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?

[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.

[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
}

[StudentScripter]

bumping this

[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.

[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?

[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.

[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?

[SGaist]

@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.