Thanks for your reply. ObservableCollection <T> is not required to , enough IEnumerable <T>. I want to see an example how to implement MVVM pattern with SfCalendar. I mean how to bind collection from ViewModel to a ItemSource of SfCalendar and show collection items on SfCalendar days in XAML. I need handle click events on SfCalendar days and transition to View with day parameter. Best regards Dmitry.