title: WPF: Bind Collection with Collection to a ListBox with groups
body: <p>sometimes WPF is too complex for me. I've got my "Window1" holding a collection of "Group"s. "Group" is a class with a collection of "Person"s. In the end this should be a contact list. What I simply want to do is to show the groups with its person in a ListBox, where the group name of the list groups equals the Name Property of my class "Groups".</p>
  
  <p>I've tried with a CollectionViewSource bound to the "Collection". The groups are shown correct, but the items of the list are equal to the group names. So each group has only one item: its group name.</p>
  
  <p>Many examples here show the grouping of items with only one collection. What I can do is to set the group name as Property of "Person". But then I can't count (and that is really neccessary):
   - how many persons are in each group
   - how many of that persons have the "Status" "Online".</p>
  
  <p>I use linq in the "Group" class to count that.
  Thanks for any advice helping me to get started.</p>