[Request] TreeView C++ model to qml example

Pheelbert

I found this example for creating a tree model: http://doc.qt.io/qt-5/qtwidgets-itemviews-simpletreemodel-example.html

The issue is that using the model in the qml doesn't display anything, and creating the QTreeView instead DOES show it correctly..

main.cpp (without main def):

QGuiApplication app(argc, argv);
QQmlEngine engine;

QString data = ...
MyTreeModel myTreeModel = MyTreeModel(data);
engine.rootContext()->setContextProperty("MyTreeModel", &myTreeModel);

QQmlComponent component(&engine, QUrl("qrc:/main.qml"));
component.create();
return app.exec();

main.qml:

ApplicationWindow {
    title: "TestWindow"
    width: 640
    height: 480
    visible: true

    TreeView {
        id: treeView
        anchors.fill: parent
        model: MyTreeModel
    }
}

If instead of executing the qml I do this, it shows correctly (same model instantiation beforehand):

[...]
QApplication app(argc, argv);
QTreeView tree;
tree.setModel(&myTreeModel);
tree.show();

p3c0

Hi @Pheelbert,
I think you may have missed re-implementing roleNames function in the model. QML views rely on these. Without them the model doesn't understand what to return. I had explained a similar one here. So basically you have to add the following in C++ model:

re-implement roleNames
define the role names

QHash<int, QByteArray> MyModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles[TitleRole] = "Title";  //these should match exactly with that in QML
    roles[SummaryRole] = "Summary"; //these should match exactly with that in QML
    return roles;
}

enum TreeRoles {
    TitleRole = Qt::UserRole + 10,
    SummaryRole = Qt::UserRole + 11
};

Apart from that I hope you have initialized the model and set it as a context Property to access it from QML.
For eg:
in main.cpp or any where as per you need

TreeModel model;

QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("myModel",&model);
engine.load(QUrl(QStringLiteral("qrc:/main.qml"))); //access myModel in QML

Pheelbert

@p3c0 Thank you so much, I also had to change to this too afterwards (removed the check if role != Qt.DisplayRole ):

QVariant MyTreeModel::data(const QModelIndex& index, int role) const {
    if (!index.isValid())
        return QVariant();

    MyTreeItem* item = static_cast<MyTreeItem*>(index.internalPointer());

    switch (role) {
    case TitleRole:
        return item->data(0);
    case SummaryRole:
        return item->data(1);
    default:
        return QVariant();
    }
}

Also, there's a "root item" that I would much rather not have; not a big deal I'll find a way work around that!

p3c0

@Pheelbert Yes missed the mentioning of data() here.
You're Welcome :-) Happy Coding.