Using C++ Models with Qt Quick Views not working

Slash200

Hello,

I have customtype as a model for qml.
Registering on Qt side is working.
But the data isn't shown in QML.
This is the QML:

import QtQuick 2.8
import QtQuick.Controls 2.3
import QtQuick.Window 2.2
import com.powertune 2.0
import QtQuick.Extras 1.4

ApplicationWindow  {
    visible: true
    width: 800
    height: 480
    minimumWidth: 800
    minimumHeight: 480
    title: qsTr("PowerTune 2.0")
    color: "grey"


    ListView {
        width: 100; height: 100

        model: qmlDataSourceModel
        delegate: Rectangle {
            height: 25
            width: 100
            Text { text: name }
        }
    }
}

Here it is registered:

#include "connect.h"
#include "updreceiver.h"
#include "datasourceobject.h"
#include <QDebug>
#include <QQmlContext>
#include <QQmlApplicationEngine>
#include <QQmlEngine>


Connect::Connect(QObject *parent) : QObject(parent)
{


     m_UpdReceiver = new UpdReceiver();
    //this Object contains all datasources as Object! Definition in datasourceobject.h!
    auto m_datasourcelist = m_UpdReceiver->initDataSources();


    //Create connection to QML Application
    QQmlApplicationEngine *engine = dynamic_cast<QQmlApplicationEngine*>( parent );
    if (engine == Q_NULLPTR) return;
    //Link m_datasourcelist to Model on QML side
    qmlRegisterType<DataSourceObject>("com.powertune", 2 , 0, "dataSourceModelObject");
    engine->rootContext()->setContextProperty("qmlDataSourceModel", QVariant::fromValue(m_datasourcelist));

    //m_UpdReceiver starts now to listen to incoming UDP packages
    m_UpdReceiver->startUdpReceiver();

}

And this the class for the model:

#ifndef DATASOURCEOBJECT_H
#define DATASOURCEOBJECT_H

#include <QObject>

//![0]
class DataSourceObject : public QObject
{
    Q_OBJECT

    Q_PROPERTY(int id READ id WRITE setid NOTIFY idChanged)
    Q_PROPERTY(QString name READ name WRITE setname NOTIFY nameChanged)
    Q_PROPERTY(QString displayname READ displayname WRITE setdisplayname NOTIFY displaynameChanged)
//![0]
public:

    //Constructors and destructors
    DataSourceObject(QObject *parent=nullptr);
    DataSourceObject(const int &id, const QString &name, const QString &displayname, QObject *parent=nullptr);
    DataSourceObject(const DataSourceObject&); //copy constructor
    ~DataSourceObject()=default;


    int id() const;
    void setid(const int &id);

    QString name() const;
    void setname(const QString &name);

    QString displayname() const;
    void setdisplayname(const QString &displayname);

signals:

    void idChanged();
    void nameChanged();
    void displaynameChanged();

private:

    int m_id;
    QString m_name;
    QString m_displayname;
//![1]
};
//![1]
Q_DECLARE_METATYPE(DataSourceObject)


#endif // DATASOURCEOBJECT_H

Debugging shows that m_datasourcelist has 8 *QObjects, so data is available.
Output shows no errors

raven-worx

@Slash200
http://doc.qt.io/qt-5/qqmllistproperty.html

The QQmlListProperty class allows applications to expose list-like properties of QObject-derived classes to QML.

Slash200

@raven-worx
I'm coming from this manual:
http://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html
So this is no the correct way to do it?

raven-worx

@Slash200 said in QObjectList-based Model not working:

Rectangle {
height: 25
width: 100
color: "black"
Text { text: name }
}

may it be possible that you show black text on black background? :)

Slash200

@raven-worx
No, I changed the color and there is also nothing visible

Slash200

@raven-worx
I found out, when I add items to the QList directly in the class that has engine->rootContext()->setContextProperty("qmlDataSourceModel", QVariant::fromValue(m_datasourcelist)); in it, it's working.

But in my code the QList is "filled" with QObjects* that are returned from class m_UpdReceiver.

Any Ideas how to solve this?

Gojir4

@Slash200 Hi,

I guess you have followed the QObjectList based model, which is not really a good one. Did you notify the note at the end which say "Note: There is no way for the view to know that the contents of a QList has changed. If the QList changes, it is necessary to reset the model by calling QQmlContext::setContextProperty() again." ?

This means that when using this kind of "model", you need to recall QQmlContext::setContextProperty() each time your list as changed, otherwise you will not see the changes on the QML side.

I would recommend to follow the QAbstractItemModel Subclass to make your model. This also offers the advantage that you can eventually remove inheritance from QObject with your class DataSourceObject, which is, in my opinion, a better architecture. Try to avoid as much as possible to use list of QObject* to store data.

Slash200

Hello,

I solved the problem by changing the type QList from <datasourceobject*> to <QObject*>
Thank you very much for your help!