setSelectionModel in QListWidget stops emission of itemSelectionChanged signal - c++

Question

In my QListWidget subclass, when I replace its QItemSelectionModel using setSelectionModel, the list widget stops emitting its itemSelectionChanged signal. In the real code, I'm doing this to install a subclass of QItemSelectionModel, but the problem appears even if I use just a new QItemSelectionModel.
MyListWidget::MyListWidget(QWidget* parent)
: QListWidget(parent)
{
QItemSelectionModel* oldSelectionModel = selectionModel();
QItemSelectionModel* newSelectionModel = new QItemSelectionModel(model(), oldSelectionModel->parent());
setSelectionModel(newSelectionModel);
oldSelectionModel->deleteLater();
}
In the debugger, I can see QItemSelectionModel emit its selectionChanged signal, but QListWidget never emits its corresponding itemSelectionChanged signal.
If I comment out the body of this constructor, things work fine. As before, I can see QItemSelectionModel emit its selectionChanged signal, but now that triggers QListWidget to emit itemSelectionChanged.
It looks as if my call to setSelectionModel causes the connection between QItemSelectionModel::selectionChanged and QListWidget::itemSelectionChanged to break.
By the way, I checked to see if I'm passing the wrong arguments to my new QItemSelectionModel. After I create it, model() and parent() of newSelectionModel are identical to those of oldSelectionModel. I also tried commenting out the call to deleteLater, but that didn't help.
Any help much appreciated.

Answer 1

As per the Qt documentation of QAbstractItemView, setSelectionModel replaces the current selection model and it won't work if setModel() is called after this.
Note that, if you call setModel() after this function, the given
selectionModel will be replaced by one created by the view.
Also, from QListWidget documentation,
QListWidget is a convenience class that provides a list view similar
to the one supplied by QListView, but with a classic item-based
interface for adding and removing items. QListWidget uses an internal
model to manage each QListWidgetItem in the list.
it looks like whenever you add items, the model gets updated / refreshed invalidating your custom selection model (just my thought).
Also, you don't need to delete the old selection model as per Qt docs
Note: It is up to the application to delete the old selection model if
it is no longer needed; i.e., if it is not being used by other views.
This will happen automatically when its parent object is deleted.
However, if it does not have a parent, or if the parent is a
long-lived object, it may be preferable to call its deleteLater()
function to explicitly delete it.
if you want that level of customisation, QListView might be a better option.
QListWidget
QAbstractItemView
Just wondering, have you tried setting custom selection model after adding all the items to the list widget?

Answer 2

This turned out to be a Qt bug. See my two posts on the Qt Forums and the bug report:
http://forum.qt.io/topic/63676/qlistwidget-how-to-prevent-unselect-all/2
http://forum.qt.io/topic/63674/qlistwidget-setselectionmodel-stops-emission-of-itemselectionchanged-signal
https://bugreports.qt.io/browse/QTBUG-50891