QAbstractModel insert row at the top, keep current item selected

[alketi]

I have a very simple QAbstractModel for a flat QTreeView (no children).

I use an external data structure to return a value for the data() method, shown below.

QVariant MyModel::data(const QModelIndex &index, int role) const
{
  if (!index.isValid())
    return QVariant();
 
  if (role != Qt::DisplayRole && role != Qt::EditRole)
    return QVariant();
 
  if (index.column() == 0)
    return m_data->getSize() - index.row();
 
  return QVariant();
}

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

  if (role != Qt::DisplayRole && role != Qt::EditRole)
    return QVariant();

  if (index.column() == 0)
    return m_data->getSize() - index.row();

  return QVariant();
}

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This just simply provides a reverse ordered list for the first column, with the newest numbers arriving on top. AKA --

4
3
2 <-- User has this selected
1

So, when new data arrives, my m_data vector is incremented (outside of the model), and I call layoutChanged() on the model.

The issue is that I want the user to be able to select a particular item, say #2, and have that selection stay on #2, even when a 5th element is added to the top.

What happens is that the selection doesn't follow the item, but rather stays in the same position -- presumably because the items aren't being "inserted" correctly.

5
4
3 <-- Selection stays here: in the same list position when a 5th item is added
2 <-- I want the selection to remain with the number that was previously selected
1

I've tried various combinations of beginInsertRows(), endInsertRows(), layoutAboutToBeChanged(), to no avail.

I've even thought of trying to store the current selection and replace it after adding data, though I suspect this will fire some selection events that I'll need to filter.

Is there an easy way to handle this without embedding the data structure inside the model?

[wysota]

You should use beginInsertRow() followed by endInsertRows() followed by dataChanged() for the first column (since data in all rows changes).

[anda_skoa]

You should use beginInsertRow() followed by endInsertRows() followed by dataChanged() for the first column (since data in all rows changes).

Shouldn't the begin/end insert rows duo be enough?
The value of the other rows stay the same, no?

Something like

// insert row, top level, at row 0
beginInsertRows(QModelIndex(), 0, 0);
 
//prepend row to m_data
 
endInsertRows();

// insert row, top level, at row 0
beginInsertRows(QModelIndex(), 0, 0);

//prepend row to m_data

endInsertRows();

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Cheers,
_

[wysota]

Ah, right, of course.