I tried to implement a quickfilter (filtering the current view, showing only the torrents that match), but actually abandoned the idea after getting confused by KTorrentView and ViewManager. I'm really not sure where should the actual filtering happen.

Perhaps you'd have any pointers, George and Ivan?

A KTorrentView shows all torrents which are member of a Group. (Group::isMember)

If you want to filter, I would do the filtering in the Group class,

I would propose you add an isMember function which takes the filter as an additional parameter, which then just calls the regular isMember function and additionally checks the filter.