ScheduleView AppointmentsSource binding issue

[Cheau-Long]

Hi Telerik,
My ScheduleView binds AppointmentsSouce to a VM like

        public ObservableCollection<Appointment> Appointments
        {
            get
            {
                return _appointments;
            }
            set
            {
                _appointments = value;
            }
        }

When creating an appointment by dragging item from other control like ListView, the binding won't fire in the VM, however when I checked the appointments collection in runtime, it was added correctly. My question is how can I track this event (not in code behind) in VM when an appointment item is added to ScheduleView?

Thanks.
Cheau