QTableView with QAbstractTableModel derrived class not displaying data

[Calvin H-C]

I am trying to use a QTableView to display information using a class derived from QAbstractTableModel, but it is not displaying and using debug lines I have confirmed that data() is never being called.

I've looked at numerous versions of this problem but so far have not found a solution for my situation - unlike many I have looked at, I am not creating either the view or model on the stack.

The QListView itself is defined in MainWindow.ui - it is a child of a QHBoxLayout that is a child of a centalwidget of the QMainWindow.

First here is the declaration for the model, RailDocModel:

class RailDocModel : public QAbstractTableModel
{
	Q_OBJECT

private:
	QList<LayoutObject *> Elements;

public:
	enum RailDocRoles
	{
		SampleRole = Qt::UserRole,
	};
	explicit	RailDocModel( QObject * = nullptr );
	int			columnCount( const QModelIndex & = QModelIndex() ) const override;
	int			rowCount( const QModelIndex & = QModelIndex() ) const override;
	QVariant	data( const QModelIndex &, int ) const override;
	QVariant	headerData( int, Qt::Orientation, int ) const;
	void		operator<<( LayoutObject * );
};

Here is he implementation (for test purposes, I am only returning a QString containing the row and column number in data() ):

RailDocModel::RailDocModel( QObject * parent ) :
	QAbstractTableModel{ parent }
{}

int RailDocModel::columnCount( const QModelIndex & parent ) const
{
	Q_UNUSED( parent )
	return LayoutObject::nFields;
}

int RailDocModel::rowCount( const QModelIndex & parent ) const
{
	Q_UNUSED( parent )
	return Elements.count();
}

QVariant RailDocModel::data( const QModelIndex & index, int role ) const
{
	if (role == Qt::DisplayRole)
		return QString( "Row%1, Column%2" )
				.arg( index.row() + 1 )
				.arg( index.column() + 1 );

	return QVariant();

}

QVariant RailDocModel::headerData( int section, Qt::Orientation orientation, int role ) const
{
	switch( role )
	{
		case Qt::DisplayRole:
			return LayoutObject::GetHeader( section );

		default:
			return QAbstractTableModel::headerData( section, orientation, role );
	}
}

void RailDocModel::operator<<( LayoutObject * NewElement )
{
	Elements << NewElement;
}

Here is MainWindow ():

MainWindow::MainWindow( QWidget *parent )
	: QMainWindow( parent ),
	  ListModel( new RailDocModel( this ) ),
	  pDoc( new RailDoc( AppSettings, *ListModel ) ),
	  ui( new Ui::MainWindow )
{
	int	i;

	ui->setupUi( this );
	statusBar()->showMessage( tr( "Ready" ) );
	List = ui->centralwidget->findChild<QTableView*>( "ElementView" );
	List->setModel( ListModel );
	List->setSelectionBehavior( QAbstractItemView::SelectRows );
	List->setSelectionMode( QAbstractItemView::SingleSelection );
	List->horizontalHeader()->setDefaultAlignment( Qt::AlignLeft );
	for( i = 0; i < LayoutObject::nFields; i++ )
		List->setColumnWidth( i, LayoutObject::GetHeaderWidth( i ) );
	List->setEditTriggers( QAbstractItemView::NoEditTriggers );
	QObject::connect( statusBar(), &( statusBar()->messageChanged ), this, &OnStatusMessageChanged );
}

The lines that set the header text (in my model) and column width (in MainWindow()) work properly.

I figure I am blind to something simple that I am missing, but after a week of going over this and trying dozens of things, I hope someone can see what I don't.

[Christian Ehrlicher]

@Calvin-H-C said in QTableView with QAbstractTableModel derrived class not displaying data:

Elements

I don't see where you fill this container.

void RailDocModel::operator<<( LayoutObject * NewElement )
{
	Elements << NewElement;
}

And here you're missing some important signals: https://doc.qt.io/qt-6/model-view-programming.html#inserting-and-removing-rows

[Calvin H-C]

@Christian-Ehrlicher said in QTableView with QAbstractTableModel derrived class not displaying data:

Elements

I don't see where you fill this container.

Sorry, I should have mentioned that Elements is being filled, and has been tested. I was originally using a QListView with QStringListModel which worked to show that Elements was being filled. When I switched to QTableView and QAbstractTableModel I had added a debug statement to rowCount() to also confirm that Elements was filled.

void RailDocModel::operator<<( LayoutObject * NewElement )
{
	Elements << NewElement;
}

And here you're missing some important signals: https://doc.qt.io/qt-6/model-view-programming.html#inserting-and-removing-rows

That pointed me to what I was missing. Changing operator<<() to this was the solution:

void RailDocModel::operator<<( LayoutObject * NewElement )
{
	beginInsertRows( QModelIndex(), Elements.count(), Elements.count() );
	Elements << NewElement;
	endInsertRows();
}

I had tried adding beginInsertRows() and endInsertRows() recently, but had used nullptr as the first parameter to beginInsertRows() instead of QModelIndex().