or

ganttTask.Start = DateTime.MinValue;ganttTask.End = DateTime.MinValue;public ScheduleItem SelectedItem { get { return _selectedItem; } set { _selectedItem = value; // SomeType : IGanttTask and for all items of SomeType the next comes true: //Start = DateTime.MinValue; // End = DateTime.MinValue; if (_selectedItem is SomeType) { EventsPanel.HorizontalOffset = HorisontalPannelOffset; } RaisePropertyChanged(() => SelectedItem); } }