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

[A Former User]

@SGaist : I am getting this data when user clicks left mouse button. I have slot, so when user clicks button some magic is done and later i save in model member variable Info_.
The NewStructInfo looks like this:
struct NewStructInfo{
double x;
double y;
} Info_;
So now my model data categories_ looks something like this:
```
Property ----------------------------------------- Value
-->Coordinates(categoryitem pointer)
------X (scenariopropertyitem1 pointer type) ------ "Empty"
------Y (scenariopropertyitem pointer type) -------- "Empty"

The above structure you can see in parsejsonobject member function. Now in the above categories_ model data i have iterate along category->secnariopropertyitem and look for the name i,e,

if(scenariopropertyitem->name == x)
// scenariopropertyitem pointer has name as class member
scenariopropertyitem->setValue(QVariant(Info_.X));
Now somehow dataChanged(??,??,Qt::displayrole) has to be called.

[SGaist]

Since you have to go through your model to find the correct item to update, you should already have the index matching the scenariopropertyitem you found, no ?

[A Former User]

@SGaist : How would i access it or get the index of the item? Meanwhile would you suggest me to use third option from this answer: https://stackoverflow.com/questions/29921041/getting-the-index-for-a-given-item-in-a-qtreeview-model-application.
Could you provide an example?

[A Former User]

This post is deleted!

[A Former User]

This post is deleted!

[VRonin]

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

[A Former User]

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.

[JonB]

@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??

[A Former User]

@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.

[JonB]

@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?

[A Former User]

@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?

[JonB]

@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.

[A Former User]

@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.

[JonB]

@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.

[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

[A Former User]

@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.

[A Former User]

@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

[A Former User]

@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.