Suggestions

[balintn22]

Hi Ishrak,
I see it's fairly old code, but I found it relly helpful.
Some suggestions:

• you might want to remove unused using statements
• in HotelsGroupViewModel, you have a property and a backing variable (items and Items).
  In the constructor (lines 30-31) you initialise them both, one would be enough.
• HotelViewModel is derived from ObservableRangeCollection
  This is a big no-no in programming in general, however, in this case it is a key part of the implementation, you might want to add a comment about it: ListView requires a collection of a collection of items (List<List>). The only way you can achieve this if HotelViewModel IS a collection of RoomViewModels, it can't be implemented as a type with a property holding the collection of those.