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

VRonin

@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

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@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();
}

JonB

@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.

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@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?

VRonin

@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

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@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;
}

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

VRonin

@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.

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

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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;
        }
    }
}

VRonin

@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

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@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:

I tried to comment in the debug output and i get the following:

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This post is deleted!

VRonin

@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);

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@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.

VRonin

@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

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@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;
}

VRonin

@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?

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@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();
    }
}

VRonin

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

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@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?