QAbstractTableModel retrieve custom object on data changed

Question

I have recently picked up Qt again, and started refreshing my memory. Creating a custom data model for a table was easy enough.

Now I am trying to retrieve the selected data. Take note that I use custom data objects.

Example of my custom model:

platform.h

class Platform
{
public:
    Platform();
    Platform(QString name);
    QString getName();
    void setName(QString name);
private:
    QString m_name;
};

Very simple data structure for testing purposes. I then implemented a QAbstractTableModel, the Data() method looks like this:

platformmodel.cpp

QVariant PlatformModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid())
        return QVariant();

    if (index.row() >= m_platforms.size() || index.row() < 0)
        return QVariant();

    if (role == Qt::DisplayRole) {
        Platform platform = m_platforms.at(index.row());
        qDebug() << platform.getName();
        return platform.getName();
    }
    return QVariant();
}

What I understand from this code is, that for the selectable items, a String is always returned, instead of a platform object.

For displaying, this works fine, I see the actual objects in the view. Now I want to select the actual object from the model, and not just a QString.

So the method body would be something like:

void MainWindow::selectionChangedSlot(const QItemSelection &, const QItemSelection &)
{
    //get the text of the selected item
    const QModelIndex index = ui->lvPlatforms->selectionModel()->currentIndex();
    Platform selectedPlatform = index.data();//This returns a QVariant and will fail at compile time, but I want to achieve something along this line.
    setWindowTitle(selectedPlatform.getName());
}

P.s. Maybe I am trying to search on the wrong thing, I can find examples that use custom objects, but none talk about retrieving the selected item.

There has to be a better way then retreiving the string, then looping trough the list of platforms and comparing the name to the selected item.. If i have a big list, having to loop trough each item and do string comparison is not very efficient.

I hope my problem is clear enough. If something important lacks, let me know so I can edit my example.

EDIT

I tried Q_DECLARE_METATYPE(Platform);

And yes it works, it makes it possible to store it in a QVariant, the problem is, since for displaying, a String is always expected, or 9/10 times anyway. So far it seems impossible to have both text display AND get the full platform object from the selection model(i can do both individually.. pretty useless..)

Answer 1

You can create custom type compatible with QVariant using the macro Q_DECLARE_METATYPE. If you declare your class as a metatype, you can store it in a QVariant and extract it with a cast.

Here an example that show how to create a custom delegate which can display data from a custom class using QVariant :

class Data {
private:
    QString name;
    int value;
public:
    Data() : name(""), value(-1){}
    Data( QString n, int v ) : name(n), value(v){}
    QString text() {
        return QString( "Test %1 - %2" ).arg( name ).arg( value );
    }
};

Q_DECLARE_METATYPE( Data )

class Delegate : public QStyledItemDelegate {
protected:
    void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const {
        Data d = index.data().value<Data>();
        painter->drawText( option.rect, d.text() );
    }
};


int main( int argc, char **argv) {
    QApplication app(argc, argv, true);

    QVariant var0, var1, var2;
    var0.setValue(Data( "Item A", 0 ));
    var1.setValue(Data( "Item B", 1 ));
    var2.setValue(Data( "Item C", 2 ));

    QListView *view = new QListView();
    QStandardItemModel model(3, 1);

    model.setData( model.index( 0, 0 ), var0 );
    model.setData( model.index( 1, 0 ), var1 );
    model.setData( model.index( 2, 0 ), var2 );
    view->setModel( &model );
    view->show();
    view->setItemDelegate( new Delegate() );
    return app.exec();
}