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How to modify the data in the model and update the view when new data is received from external?



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  • What I always suggest is that if you are not 100% confident in your model design (and, believe me, it's a hard) just use QAbstractItemModel* model = new QStandardItemModel(parent). Then use insertRows, insertColumns, and setData to setup your model



  • In my Model.cpp i did the following:

        emit beginResetModel();
        for (auto& category : categories_) {
            category->entryAt(0)->setValue(1);
            // for testing  i just set randomly my data value to 1
        }
        emit endResetModel();
    

    But after above changes the view is not displaying the new values.



  • @VInay123
    I don't see any entryAt() function in Qt. So what type is category, what does category->entryAt(0)->setValue(1) do in the way of setting anything in the model??



  • @JonB: If you see my code Category is a class which has entryAt() function which returns back the propertyitem. So here i am setting the model data i.e. my categories_ member variable in the model class.



  • @VInay123
    OK for entryAt(). But where in your code does entryAt(0)->setValue(1) call QAbstractModel::setData() (http://doc.qt.io/qt-5/qabstractitemmodel.html#setData)? Where is the http://doc.qt.io/qt-5/qabstractitemmodel.html#dataChanged signal being emitted?



  • @JonB: That is the problem i am facing. I do not know how to call setData which in turn emits the signal dataChanged. I do not know how to get the indexes. Here the data is only coming from the "Info_" variable. If the it was via delegates or adapters i could easily get the indexes and call setData. But in my case i get in a structure and go through each item and update its value. Could you please show me how can i achieve this in my code i.e. change the value via setData?



  • @VInay123
    Your code is way too big for me to wade through.

    • If you are using QAbstractModel, you are using a model which holds data in rows & columns, right?

    • When you put some data (received from JSON parsing or whatever), you have to decide where in the model's row/column you want to put this data, right?

    • Given that row & column, you can construct a QModelIndex() (http://doc.qt.io/qt-5/qabstractitemmodel.html#createIndex) for the data.

    • Then you can pass that to your Model::setData() to set the value, and emit dataChanged(index, index) to notify your view to update.



  • @JonB : Thank you. I implemented as following in my model:

        QModelIndex index = createIndex(1, 1, categories_[0]->entryAt(0));
        this->setData(index, 11, Qt::EditRole);
    

    It is changing the value clearly. But in the view its not being displayed.



  • @VInay123
    Well at least we're getting somewhere! Check the return result of your setData(), maybe it's failing? Does (row, column) of (1, 1) exist in your model (else you need to insertRows() etc.)? Is that setData() call indeed going into your Model::setData() and doing the emit dataChanged() there (use a debugger or debug/print statements)? There's no point using both beginResetModel() & dataChanged(), and certainly not dataChanged() while still inside the beginResetModel() before the nedRestModel(). Change your code accordingly.



  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    CategoryItem& parentItem = currentItem->parentItem();
    return createIndex(currentItem->row(), 0, &parentItem);

    This is using the address of a temp item, it will not work.

    QString data = file.readAll();

    does not handle win/lunix line endings and encodings, use QString data = QTextStream(&file).readAll();


    Use the model test to make sure your subclass works correctly



  • @JonB: Yes, I just call the setData ane here i have printed the changed:

        if (role == Qt::EditRole && index.column() == 1 && index.isValid()) {
            auto currentItem = static_cast<ScenarioPropertyItem*>(index.internalPointer());
            if (currentItem) {
                currentItem->setValue(value);
                qDebug() << currentItem->data(index.column());
                emit dataChanged(index, index);
                return true;
            }
        }
    

    The value is being changed here. The output looks like

    QVariant(int, 11)
    

    I have included a debug output in Data() but this is printing the default values that is empty("").

    QVariantModel::data(const QModelIndex& index, int role /*= Qt::DisplayRole*/) const {
        if (!index.isValid()) {
            return QVariant();
        }
    
        if (role == Qt::DisplayRole && isCategory(index)) {
            const auto currentCategory = static_cast<CategoryItem*>(index.internalPointer());
            if (index.column() == 0) {
                return currentCategory->displayName();
            } else {
                return QVariant();
            }
        }
    
        const auto currentItem = static_cast<ScenarioPropertyItem*>(index.internalPointer());
        if (role == Qt::DisplayRole && !isCategory(index)) {
            qDebug() << currentItem->data(index.column()); // Here its empty
            return currentItem->data(index.column());
        }
        return QVariant();
    }
    
    


  • @VInay123
    At this point I don't know any more. Maybe someone else does. We have described how things work. You might like to set up a tiny much simplified example to test how it all works, or look on the web for other examples and start from there.



  • @VRonin: With the test i got an error:

      // Common error test #2, make sure that a second level index has a parent
        // that is the first level index.
    

    What does above mean and how does it fit in my code?



  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    What does above mean and how does it fit in my code?

    It means that if model->hasChildren(parent) is true then index(0,0,parent).isValid() must be true and index(0,0,parent).parent()==parent.
    One of these 2 conditions is violated in your model.

    Again I strongly suggest you use QStandardItemModel rather than wasting time reimplementing your own



  • @VRonin: My class looks good:

    QModelIndex Model::parent(const QModelIndex& index) const {
        if (!index.isValid()) {
            return QModelIndex();
        }
    
        if (isCategory(index)) {
            return QModelIndex();
        }
    
        const auto currentItem = static_cast<ScenarioPropertyItem*>(index.internalPointer());
        CategoryItem& parentItem = currentItem->parentItem();
    
        return createIndex(currentItem->row(), 0, &parentItem); // Here the row is always 1.. is it right??
    }
    
    int Model::rowCount(const QModelIndex& parent /*= QModelIndex()*/) const {
        if (parent.column() > 0) {
            return 0;
        }
    
        if (!parent.isValid()) {
            return static_cast<int>(categories_.size());
        }
    
        if (isCategory(parent)) {
            const auto currentCategory = static_cast<CategoryItem*>(parent.internalPointer());
            return currentCategory->entryCount();
        }
    
        return 0;
    }
    
    int Model::columnCount(const QModelIndex& parent /*= QModelIndex()*/) const {
        return 2;
    }
    

    0_1535713717270_Capture.PNG

    Coordinates are my categories and S, T are scenariopropertiesitem. Items has category as parents. Categories dont have parents.



  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    My class looks good:

    It doesn't. as I mentioned above

    @VRonin said in How to modify the data in the model and update the view when new data is received from external?:

    CategoryItem& parentItem = currentItem->parentItem();
    return createIndex(currentItem->row(), 0, &parentItem);

    This is using the address of a temp item, it will not work.



  • @VRonin: Oh.. How could this be fixed? I have to stick to QAbstractItemModel.
    This is from Qt:
    0_1535716942348_qq.PNG



  • My row method was wrong and after updating i have a new failure in the test:

                // Check that we can get back our real parent.
                //qDebug() << "TTT 1: " << model->parent(index);
                //qDebug() << "TTT 2: " << parent;
                //qDebug() << "TTT 3: " << index;
                tmp = model->parent(index);
                Q_ASSERT(tmp == parent);
    

    At the above point i.e. line 375 its failing.
    My old row function in item used to always give 1 which was wrong. Now i made it to look at the parent and find the position.

    int ScenarioPropertyItem::row() const {
        int count = parentItem_.entryCount();
        for (int i = 0; i < count; i++) {
            if (this->displayName_ == parentItem_.entryAt(i)->displayName_) {
                return i;
            }
        }
    }
    
    


  • @VInay123 How can parentItem_ not be a pointer? if you are taking a copy of the parent and store it in the child, you'll never go back to the old parent



  • @VRonin: It is taken as reference to an unique_pointer. Now i have changed it as following:

    QModelIndex Model::parent(const QModelIndex& index) const {
        if (!index.isValid()) {
            return QModelIndex();
        }
    
        if (isCategory(index)) {
            return QModelIndex();
        }
    
        const auto currentItem = static_cast<ScenarioPropertyItem*>(index.internalPointer());
        CategoryItem* parentItem = currentItem->parentItem();
    
        return createIndex(currentItem->row(), 0, parentItem);
    }
    

    Please have a look at the index implementation also:

    QModelIndex Model::index(int row, int column, const QModelIndex& parent /*= QModelIndex()*/) const {
        if (!hasIndex(row, column, parent)) {
            return QModelIndex();
        }
    
        if (!parent.isValid()) {
            return createIndex(row, column, categories_.at(row).get());
        }
    
        const auto currentCategory = static_cast<CategoryItem*>(parent.internalPointer());
        ScenarioPropertyItem* currentItem = currentCategory->entryAt(row);
    
        if (currentItem) {
            return createIndex(row, column, currentItem);
        } else {
            return QModelIndex();
        }
    }
    

    Tried the test again but its failing at 340 at the same place:
    0_1535718574820_qq.PNG

    I tried to comment in the debug output and i get the following:
    0_1535718651532_qq.PNG



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  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    I tried to comment in the debug output

    Good. If you check it you realise that the problem is that model->parent(index) returns an item with row==1 while the original parent had row==0. that's because in parent() you are return createIndex(currentItem->row(), 0, parentItem); instead of return createIndex(parentItem->row(), 0, parentItem);



  • @VRonin Yes you are right, i have to fix it. Parent item does not have any parent so how should i save the position i.e. row for every parent? In my case the categories are parents, so i cant actually query the position in the class. One way i see is to save the row as member variable while creating the parent.



  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    One way i see is to save the row as member variable while creating the parent.

    It's one way but usually it becomes unmanageable if you implement insert/remove/moveRows

    You can always traverse categories_ to find the index of parentItem



  • @VRonin: So now the test is running error free. This was the implementation i had to make:

    QModelIndex Model::parent(const QModelIndex& index) const {
        if (!index.isValid()) {
            return QModelIndex();
        }
    
        if (isCategory(index)) {
            return QModelIndex();
        }
    
        const auto currentItem = static_cast<ScenarioPropertyItem*>(index.internalPointer());
        CategoryItem* parentItem = currentItem->parentItem();
        int rowNum = categories_.size();
        for (int i = 0; i < rowNum; i++) {
            if (categories_.at(i)->displayName() == parentItem->displayName()) {
                rowNum = i;
            }
        }
        return createIndex(rowNum, 0, parentItem);
    }
    

    But the view is still not displaying the new values. :( This is how i update the value

        QModelIndex index = createIndex(1, 1, categories_[0]->entryAt(0));
        this->setData(index, 11, Qt::EditRole);
    

    My SetData:

    bool Model::setData(const QModelIndex& index, const QVariant& value, int role /*= Qt::EditRole*/) {
        if (role == Qt::EditRole && index.column() == 1 && index.isValid()) {
            auto currentItem = static_cast<ScenarioPropertyItem*>(index.internalPointer());
            if (currentItem) {
                currentItem->setValue(value);
                emit dataChanged(index, index);
                return true;
            }
        }
        return false;
    }
    


  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    But the view is still not displaying the new values

    Does the view display the old values or is it completely empty? is currentItem null?



  • @VRonin: I initialize the model data i.e. categories_ with empty values. So the view shows empty value. But i update the value in my function and in debug mode i see the new value in the variable but the view shows empty i.e. old value. If i change the property to write mode, via delegate the value is being changed and view displays correctly. But when i do as following it does not:

        QModelIndex index = createIndex(1, 1, categories_[0]->entryAt(0));
        this->setData(index, 11, Qt::EditRole);
    

    It actually calls the setData too and emits dataChanged. But the view is not displaying. Just for info my index method looks like this:

    QModelIndex Model::index(int row, int column, const QModelIndex& parent /*= QModelIndex()*/) const {
        if (!hasIndex(row, column, parent)) {
            return QModelIndex();
        }
    
        if (!parent.isValid()) {
            return createIndex(row, column, categories_.at(row).get());
        }
    
        const auto currentCategory = static_cast<CategoryItem*>(parent.internalPointer());
        ScenarioPropertyItem* currentItem = currentCategory->entryAt(row);
    
        if (currentItem) {
            return createIndex(row, column, currentItem);
        } else {
            return QModelIndex();
        }
    }
    


  • What version of Qt are you on?
    Usually the view ignores the dataChanged if it thinks the cell pointed by index shouldn't exist



  • @VRonin : I use Qt5.9.0. The update should have been this

        QModelIndex index = createIndex(0, 1, categories_[0]->entryAt(0)); // but not 1,1
        this->setData(index, 11, Qt::EditRole);
    

    But even then after the above change its not updating. Actually in setData there is already a index.isValid() check. The indexes looks good and also the currentItem. Should i post my model and view once again after the new changes i have done?



  • @VInay123 said in How to modify the data in the model and update the view when new data is received from external?:

    Actually in setData there is already a index.isValid() check.

    index.isValid() is an insufficient check, that's why checkIndex was introduced in Qt 5.11

    The indexes looks good and also the currentItem.

    Unfortunately sometimes that's not enough. For example, if you forget to signal the view that you inserted a row, and then emit dataChanged for an item in that row, even if the item is 100% valid in the model the view will still think the row doesn't exist and do nothing



  • @JonB @VRonin @SGaist : Something is not seeming right. I tried first to change the value using the following:

    QModelIndex index = createIndex(0, 1, categories_[0]->entryAt(0));
        this->setData(index, 11, Qt::EditRole);
    

    And in delegate class i tried to see what the value it has but it looks like it is zero. Below is the implementation:

    QWidget *PropertyEditorItemDelegate::createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const {
        if (!index.isValid()) {
            return nullptr;
        } else if (index.column() == 0) {
            return QStyledItemDelegate::createEditor(parent, option, index);
        }
    
        const auto currentItem = static_cast<ScenarioPropertyItem *>(index.internalPointer());
        switch (currentItem->itemType()) {
            case PropertyType::DOUBLE: {
                QDoubleSpinBox *box = new QDoubleSpinBox(parent);
                auto v = currentItem->data(index.column()); // Here it is zero??? :(
                box->setValue(v.toDouble());
                return box;  // qt will handle deletion
            }
    default:
                return QStyledItemDelegate::createEditor(parent, option, index);
        }
    }
    


  • In setData could you add the qDebug as below and tell us what is printed?

    if (currentItem) {
               currentItem->setValue(value);
    qDebug() << currentItem->data(1);
    qDebug() << index.data(Qt::DisplayRole);
                 emit dataChanged(index, index);
                 return true;
            }
    


  • @VRonin :

    [16:56:03,236] [Debug] QVariant(int, 11) / My new values
    [16:56:03,237] [Debug] QVariant(int, 11) // My new values
    

    ;(
    When i change via delegate:

    [16:58:06,173] [Debug] QVariant(double, 0)
    [16:58:06,176] [Debug] QVariant(double, 0)
    

    I believe somewhere the indexes are not right. When i try to change the value(via delegate) of suppose "T" value so that i can iterate over parent and see the "S" value, here it is empty, but should be 11.



  • My model looks like this:
    0_1535729444022_model1.PNG
    0_1535729450658_model2.PNG

    In parent method i use pointer for parent item but not reference.



  • @VRonin @SGaist @JonB : I just debugged to see that after changing the value of the property via delegate does the index in the following code has the same value.

    QModelIndex index = createIndex(0, 1, categories_.at(0)->entryAt(0));
        this->setData(index, 11, Qt::EditRole);
    

    But it turns out that the index in the above is just a copy and when delegate changes the value it is not reflected in the index here. I think i am changing at a copy of the property but not the actual one.



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  • Can you show us the code for Delegate::setModelData?



  • @VRonin

     void PropertyEditorItemDelegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const {
            const auto currentItem = static_cast<ScenarioPropertyItem *>(index.internalPointer());
    
            auto setup = [this, &model, &index](auto editor, auto usage) {
                if (editor) {
                    usage(editor);
                } else {
                    QStyledItemDelegate::setModelData(editor, model, index);
                }
            };
    
            switch (currentItem->itemType()) {
                case PropertyType::DOUBLE: {
                    setup(qobject_cast<QDoubleSpinBox *>(editor), [&index, &model](QDoubleSpinBox *editor) {
                        editor->interpretText();
                        model->setData(index, editor->value(), Qt::EditRole);
                    });
                    break;
                }
                case PropertyType::INTEGER: {
                    setup(qobject_cast<QSpinBox *>(editor), [&index, &model](QSpinBox *editor) {
                        editor->interpretText();
                        model->setData(index, editor->value(), Qt::EditRole);
                    });
                    break;
                }
                case PropertyType::STRING: {
                    setup(qobject_cast<QLineEdit *>(editor), [&index, &model](QLineEdit *editor) { model->setData(index, editor->text(), Qt::EditRole); });
                    break;
                }
                case PropertyType::BOOLEAN: {
                    setup(qobject_cast<QComboBox *>(editor),
                          [this, &index, &model](QComboBox *editor) { model->setData(index, editor->currentText(), Qt::EditRole); });
                    break;
                }
                default:
                    QStyledItemDelegate::setModelData(editor, model, index);
                    break;
            }
        }
    

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