i want to have a Combobox with checkable items just like Qt Designer has to set flags for some elements.

What i have done so far: I created a model and connected it to my combobox, this model returns that the items are checkable as a flag. Everything works fine, except that the popup of the Combobox is closed when an item is clicked. How can i prevent that and set the item checked instead (I can let my model return that it is checked but i need to know which item was clicked, and the popup also needs to be redrawn after that) ?
In this thread:

someone mentioned to install an eventfilter, what exactly have i got to do?
If you got other suggestions how to make this work (without external libs) i would also be glad to hear.