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