Qt ListView doesn't show C++ model content - c++

Question

I'm creating a QList<> in C++ using a QML ListView to display it. The application runs without errors but the ListView stubbornly remains empty.
The QML will show a rectangle for the presence of each list item.
I checked the UI code by creating a list in QML.
It displays correctly for the QML created list.
Here's my QML:
import Processes 1.0
...
ListView {
id: qInterfaceList
height: parent.height;
width: parent.width;
model: myModel
orientation: ListView.Vertical
delegate:
Rectangle {
height: 30;
width: 120;
border.color: "red"
border.width: 3
}
The C++ code that creates and registers the list object:
// Register C++ classes as a QML type named Processes (version 1.0)
qmlRegisterType<Process>("Processes", 1, 0, "Process");
QQmlApplicationEngine engine;
// read the configuration file
Config conf;
if ( conf.read() )
{
QQmlContext* ctxt = engine.rootContext();
if ( ctxt )
{
qDebug()
<< "--- conf.Interfaces: "
<< conf.Interfaces.length()
;
ConfigInterface c;
QVariant v = QVariant::fromValue( conf.Interfaces );
qDebug()
<< "--- ConfigInterface: "
<< v
<< "--- typeName: "
<< v.typeName()
;
ctxt->setContextProperty("myModel", QVariant::fromValue( conf.Interfaces ));
}
}
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
To debug I output information about list from C++ and QML:
In C++ the count of list items is correct.
In C++ the conversion to QVariant is working.
In QML it sees the defined list.
The debugging output:
Debugging starts
--- conf.Interfaces: 65
--- ConfigInterface: QVariant(QList<ConfigInterface*>, ) --- typeName: QList<ConfigInterface*>
qml: myModel: QVariant(QList<ConfigInterface*>)
Debugging has finished
Any ideas what's wrong or how to debug this?
Thanks
EDIT: Here's the class being used as a list item
Class declaration:
class ConfigInterface : public QObject
{
Q_OBJECT
Q_PROPERTY(QString sql READ getTag WRITE setTag NOTIFY tagChanged)
Q_PROPERTY(QString description READ getDescription WRITE setDescription NOTIFY descriptionChanged)
public:
/*explicit*/ ConfigInterface();
/*explicit*/ ConfigInterface(QObject *parent);
~ConfigInterface();
// Copy constructor needed because these are copied when added to a QList
ConfigInterface(const ConfigInterface &p2) {_tag = p2._tag; _description = p2._description; }
QString getDescription() const;
void setDescription(QString&);
QString getTag() const;
void setTag(QString&);
signals:
void tagChanged(QString);
void descriptionChanged(QString);
public:
QString _tag;
QString _description;
QString QueryTemplate;
QString ConnectString;
QString MinimumId;
};
Q_DECLARE_METATYPE(ConfigInterface*)
C++ code:
ConfigInterface::ConfigInterface()
: QObject( nullptr )
{
}
ConfigInterface::ConfigInterface(QObject* parent)
: QObject(parent)
{
}
ConfigInterface::~ConfigInterface()
{
}
QString ConfigInterface::getTag() const
{
return _tag;
}
void ConfigInterface::setTag(QString& str)
{
_tag = str;
emit tagChanged(_tag);
}

Answer 1

The main problem is caused because it has a list of ConfigInterface *, according to the examples provided in the documentation should be a list of QObject *:
class Config{
[...]
public:
QList<QObject *> Interfaces;
[...]
};
In addition to this you should get the following warning:
/..../configinterface.h:17: warning: base class ‘class QObject’ should be explicitly initialized in the copy constructor [-Wextra]
ConfigInterface(const ConfigInterface &p2) {_tag = p2._tag; _description = p2._description; }
^~~~~~~~~~~~~~~
This is caused because QObject and its derived classes must not have a copy constructor or assignment operator, For more information read the following:
http://doc.qt.io/qt-5/qobject.html#no-copy-constructor-or-assignment-operator
Another improvement is that both constructors can be united in only one, in the end their class could have the following structure:
configinterface.h
#ifndef CONFIGINTERFACE_H
#define CONFIGINTERFACE_H
#include <QObject>
class ConfigInterface : public QObject
{
Q_OBJECT
Q_PROPERTY(QString sql READ getTag WRITE setTag NOTIFY tagChanged)
Q_PROPERTY(QString description READ getDescription WRITE setDescription NOTIFY descriptionChanged)
public:
ConfigInterface(QObject *parent=Q_NULLPTR);
~ConfigInterface();
QString getTag() const;
void setTag(const QString &tag);
QString getDescription() const;
void setDescription(const QString &description);
signals:
void tagChanged(QString);
void descriptionChanged(QString);
private:
QString _tag;
QString _description;
QString QueryTemplate;
QString ConnectString;
QString MinimumId;
};
#endif // CONFIGINTERFACE_H
configinterface.cpp
#include "configinterface.h"
ConfigInterface::ConfigInterface(QObject* parent)
: QObject(parent)
{
}
ConfigInterface::~ConfigInterface()
{
}
QString ConfigInterface::getDescription() const
{
return _description;
}
void ConfigInterface::setDescription(const QString &description)
{
if(_description == description)
return;
emit descriptionChanged(description);
_description = description;
}
QString ConfigInterface::getTag() const
{
return _tag;
}
void ConfigInterface::setTag(const QString &tag)
{
if(tag == _tag)
return;
emit tagChanged(tag);
_tag = tag;
}