title: MVVM binding nested user controls
body: <p>I have MainViewModel which contains collection of tab view models. Each tab can be different type of view model (different view). When users adds new tab, the corrent type of tab view is recognized (base on view model) but it is not binded at all. For example one view model contains GridView with itemsSource set to collection but if I set breakpoint on the get property of that collection it is never hit. (but when I instantiate this view model I set this collection to new ObservableCollection so NotifyPropertyChanged event is fired) - so I suppose that data context is set wrong for the nested user control (view model)</p>