QAbstractListModel::Data() method is never called

I am trying to view a list of c++ models in qml by subclassing QAbstractListModel following this tutorial Models and Views: AbstractItemModel Example

Here is my implementation:

Item model class

class User
{
   private:
     QString m_macAddr;    
     QString m_firstName;    
     QString m_lastName;

 public:
     User();
     User(const QString &mac);
     QString macAddr() const;
     void setMacAddr(QString &mac);
  };
 User::User()
 {}
   User::User(const QString &mac){
     m_macAddr = mac;
  }     
  QString User::macAddr() const{
      return m_macAddr;
  }
  void User::setMacAddr(QString &mac){
      if(mac == m_macAddr)
          return;
       m_macAddr = mac;
  //    emit macAddrChanged();
  }

QAbstractListModel subclass

class UserListModel : public QAbstractListModel
{
    Q_OBJECT
public:
    // User model roles
    enum roles{
      macRole = Qt::UserRole + 1
    };
    UserListModel(QObject *parent = nullptr);
QModelIndex index(int row, int column,
                  const QModelIndex &parent = QModelIndex()) const override;
QModelIndex parent(const QModelIndex &index) const override;
QModelIndex getIndex(int r, int c, void *p);
int rowCount(const QModelIndex &parent = QModelIndex()) const override;
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
    void addUser(const User &user); 
private:
    QList<User> m_users;
protected:
    QHash<int, QByteArray> rolesNames() const;
};
// Class inplementation.

UserListModel::UserListModel(QObject *parent)
: QAbstractListModel(parent)
{

}

void UserListModel::addUser(const User &user){
    beginInsertRows(QModelIndex(), rowCount(), rowCount());
    m_users << user;
    endInsertRows();
}

int UserListModel::rowCount(const QModelIndex &parent) const
{
    return m_users.count();
}

QVariant UserListModel::data(const QModelIndex &index, int role) const
{
    if (index.row() < 0 || index.row() >= rowCount())
        return QVariant();
    const User &user = m_users[index.row()];
        if(role == macRole){
            return user.macAddr();
        }
        return QVariant();
    }    
QModelIndex UserListModel::index(int row, int column, const QModelIndex &parent) const
{
    return parent;
}

QModelIndex UserListModel::parent(const QModelIndex &index) const
{
    return index;
}

QModelIndex UserListModel::getIndex(int r, int c, void *p) {
    return this->createIndex(r, c, p);
}
QHash<int, QByteArray> UserListModel::rolesNames() const {
    QHash<int, QByteArray> roles;
    roles[macRole] = "mac";
    return roles;
}

main.cpp

QQmlApplicationEngine engine;
QString mac = "12:3e:3w:4r:33";
userlistModel->addUser(User(mac));
userlistModel->addUser(User(mac));
userlistModel->addUser(User(mac));
userlistModel->addUser(User(mac));
engine.rootContext()->setContextProperty("usersModel", userlistModel);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
QModelIndex id = userlistModel->getIndex(1, 0, 0);

QVariant v1 = userlistModel->data(id, Qt::UserRole + 1);

qDebug() << "===========" << v1.toString();
controller::DatabaseService<SqliteDB> *sqliteDb = new controller::DatabaseService<SqliteDB>();
if (engine.rootObjects().isEmpty())
    return -1;
return app.exec();

QML

    ListView{
        id: listView
        anchors.fill: parent
        model:usersModel
        delegate:  Component { HorizontalListItem{mac: mac}}
    }

---

The Problem is :

In main function I am adding 4 models to the list model but, They are shown in qml without data. althought, I am trying to view mac role.

---

what I tried

• I tried to add a breakpoint inside methodes rolesNames() and data() but, It seems that the compiler is not getting inside anyone of them.
• I tried to invoke data() method in main function and it returns the desired data.

It is not necessary that you override the index, or parent methods, nor do you create the getIndex method. In your case you need to implement the roleNames method:

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QAbstractListModel>
#include <QDebug>

class User
{
    QString m_macAddr;
public:
    User(){}
    User(const QString &mac): m_macAddr(mac){}
    QString macAddr() const{return m_macAddr;}
    void setMacAddr(QString &mac){m_macAddr = mac;}
};

class UserListModel : public QAbstractListModel
{
public:
    enum roles{
        macRole = Qt::UserRole + 1
    };
    explicit UserListModel(QObject *parent = nullptr)
        : QAbstractListModel(parent){}
    int rowCount(const QModelIndex &parent = QModelIndex()) const override {
        if (parent.isValid())
            return 0;
        return m_users.count();
    }
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override {
        if (!index.isValid())
            return QVariant();
        if (index.row() < 0 || index.row() >= rowCount())
            return QVariant();
        const User &user = m_users[index.row()];
        if(role == macRole)
            return user.macAddr();
        return QVariant();
    }
    QHash<int, QByteArray> roleNames() const override{
        QHash<int, QByteArray> roles;
        roles[macRole] = "mac";
        return roles;
    }
    void addUser(const User &user){
        beginInsertRows(QModelIndex(), rowCount(), rowCount());
        m_users << user;
        endInsertRows();
    }
private:
    QList<User> m_users;
};


int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    UserListModel userlistModel;
    QString mac = "12:3e:3w:4r:33";
    userlistModel.addUser(User(mac));
    userlistModel.addUser(User(mac));
    userlistModel.addUser(User(mac));
    userlistModel.addUser(User(mac));
    QModelIndex ix = userlistModel.index(1, 0);
    QVariant v = userlistModel.data(ix, UserListModel::macRole);
    qDebug() << "===========" << v.toString();
    engine.rootContext()->setContextProperty("usersModel", &userlistModel);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

main.qml

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    ListView{
        anchors.fill: parent
        model:usersModel
        delegate: Component
        {
            Text{
                text:  model.mac
            }
        }
    }
}