Using C++ Models with Qt Quick Views example

[Mark81]

I'm trying to adapt this example to my needs. Here my code:

modelcontent.h

#ifndef MODELCONTENT_H
#define MODELCONTENT_H

#include <QObject>
#include <QAbstractListModel>

class Content
{
public:
    Content(const QString &label) : _label(label)
    {
    }

    QString label() const { return  _label; }

private:
    QString _label;
};

class ModelContent : public QAbstractListModel
{
    Q_OBJECT

public:
    enum ContentRoles
    {
        LabelRole = Qt::UserRole + 1,
    };

    explicit ModelContent(QObject *parent = nullptr) : QAbstractListModel(parent)
    {
    }

    void addContent(const Content &content)
    {
        beginInsertRows(QModelIndex(), rowCount(), rowCount());
        _content << content;
        endInsertRows();
    }

    int rowCount(const QModelIndex &parent = QModelIndex()) const
    {
        Q_UNUSED(parent);
        return _content.size();
    }

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const
    {
        if (index.row() < 0 || index.row() >= _content.size()) return QVariant();

        const Content &content = _content[index.row()];
        switch (role)
        {
        case LabelRole: return content.label();
        default: return QVariant();
        }
    }

private:
    QList<Content> _content;

protected:
    QHash<int, QByteArray> roleNames() const
    {
        QHash<int, QByteArray> roles;
        roles[LabelRole] = "label";
        return roles;
    }
};

#endif // MODELCONTENT_H

flow.h

#ifndef FLOW_H
#define FLOW_H

#include <QObject>
#include "modelcontent.h"

class Flow : public QObject
{
    Q_OBJECT

public:
    explicit Flow(QObject *parent = nullptr);
    ModelContent modelContent;
};

#endif // FLOW_H

flow.cpp*

#include "flow.h"

Flow::Flow(QObject *parent) : QObject(parent)
{
    modelContent.addContent(Content("abc"));
    modelContent.addContent(Content("def"));
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "flow.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    Flow flow;

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated, &app, [url](QObject *obj, const QUrl &objUrl)
    {
        if (!obj && url == objUrl) QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.setInitialProperties({{"model", QVariant::fromValue(&flow.modelContent)}});
    engine.load(url);

    return app.exec();
}

main.qml

import QtQuick
import QtQuick.Controls

ApplicationWindow {
    id: window
    width: 1920
    height: 1080
    visible: true
    visibility: "FullScreen"
    color: "black"

    Component {
        id: delegate

        Item {
            id: item
            width: 864*0.7; height: 1536*0.7

            Text {
                required property string label
                anchors.centerIn: parent
                text: label
            }
        }
    }

    PathView {
        id: view
        anchors.fill: parent
        anchors.bottomMargin: 150
        anchors.topMargin: 50
        pathItemCount: 3
        preferredHighlightBegin: 0.5
        preferredHighlightEnd: 0.5
        highlightRangeMode: PathView.StrictlyEnforceRange
        highlightMoveDuration: 1000
        snapMode: PathView.SnapToItem
        rotation: -90

        required model

        delegate: delegate
        path: Path {
            startX: 0; startY: view.height / 2
            PathLine {x: view.width/2; y: view.height / 2; }
            PathLine {x: view.width; y: view.height / 2; }
        }
    }
}

No errors during building, but at run-time I get:

QML debugging is enabled. Only use this in a safe environment.
QQmlApplicationEngine failed to create component
qrc:/main.qml: Setting initial properties failed: ApplicationWindow does not have a property called model
qrc:/main.qml:117:5: Required property model was not initialized
12:06:36: Remote process crashed.

Line 117 is:

PathView {

I double checked the example and I didn't find anything I missed.
I just changed the setInitialProperties call from QQuickView to QQmlApplicationEngine.

Any idea?

[KroMignon]

@Mark81 said in Using C++ Models with Qt Quick Views example:

I think you will have many name clashes:

• engine.setInitialProperties({{"model", QVariant::fromValue(&flow.modelContent)}}); ==> model is a common property name for many classes, to avoid to use it a global property name!
• same with component called delegate, this is a very bad idea ==> delegate: delegate will connect delegate to itself!

first cleanup you class/component/variable naming to avoid those clashes.

[Mark81]

You should tell this to the Qt developers :-) I found this name in the linked example.
Anyway, I changed:

engine.setInitialProperties({{"modelContent", QVariant::fromValue(&flow.modelContent)}});
...
required modelContent
delegate: delegateContent

Now the errors are these:

QQmlApplicationEngine failed to create component
qrc:/main.qml: Property modelContent was marked as required but does not exist
QQmlComponent: Component destroyed while completion pending
This may have been caused by one of the following errors:
qrc:/main.qml: Property modelContent was marked as required but does not exist

[GrecKo]

The example you linked work because it was assigning to the existing model property or the ListView.

Here you would need to define a property to hold your model in the root object of your QML, the ApplicationWindow in your case:

ApplicationWindow {
     id: window
     required property QtObject model
    // ...
    PathView {
        model: window.model
        // ...
    }
}

or :

ApplicationWindow {
    property alias model: view.model
    // ...
    PathView {
        id: view
        // ...
    }
}

[Mark81]

@GrecKo Thanks, I understood ListView, GridView, PathView and so on differ for how they show the items only.
The first syntax worked, at least a bit more.

Now I have to understand how to declare the required property label.
The example used this syntax:

delegate: Text {
    required property string type
    required property string size

    text: "Animal: " + type + ", " + size
}

but it doesn't work for me:

Required property label was not initialized

I'm very sorry but I don't understand this syntax yet. I'll be very glad if you can help me to make this to work but also if there is a page in the docs that explain how to achieve this simple task.

[Mark81]

I'm not sure if this solution is ok, because is quite different from the example but at least it works:

main.cpp

engine.rootContext()->setContextProperty("modelContent", &flow.modelContent);

main.qml

PathView {
    id: view
    ...
    model: modelContent