Qt TreeView problem when used with sort model - c++

Question

I have a problem where i did not find a solution so far, actually the question is when and for what QModelIndex we have to call beginInsertColumns and similar functions.
My example is the standard Qt example from here:
http://doc.qt.io/qt-5/qtwidgets-itemviews-editabletreemodel-example.html
It is also delivered with every qt installation, e.g. C:\Qt\Qt5.12.0\Examples\Qt-5.12.0\widgets\itemviews\editabletreemodel
When just executed, it works fine, but now lets insert a QSortFilterProxyModel, just to make it sortable. We change the MainWindow c'tor to
...
QFile file(":/default.txt");
file.open(QIODevice::ReadOnly);
TreeModel *model = new TreeModel(headers, file.readAll());
file.close();
QSortFilterProxyModel* sort = new QSortFilterProxyModel( this );
sort->setSourceModel( model );
view->setModel( sort );
...
Now execute the example, expand one or two of the root nodes and select the menu entry "insert column" you will see, that only the root nodes have a new column, all their children do not have the new column. It works without the proxy. Now my question, do i have to emit beginInsertColumns for every QModelIndex that has children?
How can i fix this?
Note, this is not only a problem with qt 5.12, but also with many earlier releases.

Answer 1

I've always had problems using QSortFilterProxyModel, and as far as I understood they are often related to the index mapping between with the source model.
I managed to solve it using the QSortFilterProxyModel::invalidate() method that will reset the mapping, without spoiling the current state of the view.
Modify the MainWindow::insertColumn as follows:
bool MainWindow::insertColumn()
{
QAbstractItemModel *model = view->model();
int column = view->selectionModel()->currentIndex().column();
bool changed = false;
// Insert a column in the parent item.
QSortFilterProxyModel* sfpm = qobject_cast<QSortFilterProxyModel*>(model);
if (sfpm)
{
changed = sfpm->insertColumn(column + 1);
if (changed)
sfpm->setHeaderData(column + 1, Qt::Horizontal, QVariant("[No header]"), Qt::EditRole);
sfpm->invalidate();
}
updateActions();
return changed;
}
It is not an optimal solution, and I don't know if there is a better way, but works for me.