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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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  • Lifetime Qt Champion

    Why are you calling createIndex in onRefreshRoadInfo ?

  • @SGaist In onRefereshRoadInfo function i get the new values which has to be shown in the view. So, here I want to update the values, and as i dont have the index's, i create index for every property and call setData to update the values. If this is not correct how should i update the values here?

  • @JonB @SGaist @VRonin : Any lead for my problem?

  • Lifetime Qt Champion

    Please show more patience, allow at least 24 hours before bumping your own thread. People answering on this forum do it on a voluntary basis and might not live in the same time zone as you.

    That said, I stumble upon the QJsonModel project. You might want to check it.

  • @SGaist I will keep in mind :). I saw the project and looks like my current implementation looks but, the project does not have the one thing i am looking for i.e. updating of data inside the code i.e. onRefereshRoadInfo.

  • How is it possible that even after changing the model data value in a hard way and emitting reset model signals does not refresh the view.

    void ScenarioPropertiesModel::onRefreshRoadInfo(const NewData& roadInfo) {
        emit beginResetModel();>entryAt(0)->setValue(11111);
        emit endResetModel();

    Could it be that index function implementation is wrong? This is my index implementation:

    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,;
        const auto currentCategory = static_cast<CategoryItem*>(parent.internalPointer());
        ScenarioPropertyItem* currentItem = currentCategory->entryAt(row);
        if (currentItem) {
            return createIndex(row, column, currentItem);
        } else {
            return QModelIndex();

  • It still not clear to me in what component the problem is. Could you try to remove your custom delegate and see if it updates the values? if it doesn't then it's a model problem but at least we know where to focus

  • @VRonin: Hi Ronin, thnx for the reply. Even without delegates it is not working. I believe it lies in model. I am updating a copy of the model but not the model.
    Here below, the model pointer is always in the old state, even after changing the values in my model class.

    void Delegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index)

    For infor: I have hosted the project in Github:

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

    For infor: I have hosted the project in Github:

    Would have been nice if it compiled. Can you upload the ui and json file too?

  • @VRonin : Done.

  • I'm concentrating on the model only at the moment but it works perfectly for me.
    The only thing that I would flag is that the json that you provided has all "ReadOnly": true so it won't allow changes unless you change that to false.

    Could you try this fork and tell me what is that you expect to happen that is not happening?

  • @VRonin: Now there is a function with following signature

    void ScenarioPropertiesModel::onRefreshRoadInfo(const NewData& roadInfo) {}

    Now i would ask you to set the model data (properties) to the new values present in roadInfo variable(or to a random number) in the above function and display it in the view.

    My usecase is that, i will have a street and when user clicks on the street onRefreshRoadInfo will be called with the values which are actually coordinates and these i want to show.

  • So you are confirming that, so far, the fork above is behaving correctly?

  • @VRonin : Yes, it works correctly. :)

  • Could you check the same fork now and see if onRefreshRoadInfo does what you expect?

  • @VRonin : Hi Ronin, i checked your fork and it is working exactly as i need. So i tried to copy the code in my implementation and sadly it is not working, i even commented out the delegates. Could you please implement the ur logic in my code and see if you can make it work? I mean use the ui and view class. May be something is buggy in my view class? But there is nothing much in the view class too.

    I tried to use your main function with my implementation as below so that my view class is used. But turns out the implementation does not work.

        QApplication a(argc, argv);
        //ScenarioPropertiesModel model;
        //QTreeView w;
        PropertyEditorView view;// model creation and setting done in class constructor
     //   QPushButton sendRefreshRoadInfoButton("Refresh //Road Info");
        //QObject::connect(&sendRefreshRoadInfoButton,&QPushB//utton::clicked,&model,&ScenarioPropertiesModel::onRe//freshRoadInfo); i use my own signal and slot
        return a.exec();~~

    When i modified the main as below it is working.

        QApplication a(argc, argv);
        ScenarioPropertiesModel model;
        PropertyEditorView w;
        w.ui_->treeView->setModel(&model); // removed setting from PropertyEditorView constructor as we set here;
        QPushButton sendRefreshRoadInfoButton("Refresh Road Info");;
        return a.exec();

    Do you see any reason for this behavior.

  • Lifetime Qt Champion

    Because on your first version of the code you are not connecting to the model you have in your PropertyEditorView but the one you declared above. On a side note, that can't compile since you commented out your model declaration.

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  • @SGaist @JonB @VRonin : So i took a deep breathe and tried to implement my code from scratch using @VRonin solution i.e. his latest fork
    Now my code is working :). This was the piece of line which helped me:

        const QModelIndex parentIdx = index(0, 0);
        const QModelIndex xValueIndex = index(0, 1, parentIdx);
        setData(xValueIndex, 2.55);

    Additionally deep inside my code i had two pointers to my view which was also the cause for not showing the new values. The thread can be closed. I have a request @VRonin if he could take out the link to the code as it is a part of commercial project. Thank you everyone for your help, especially @VRonin.

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