How to add additional attributes for your appointments ?

        
    public class CustomAppointment : ScheduleAppointment
    {
        private string appointment_ID;
        public string AppointmentID
        {
            get { return appointment_ID; }
            set { appointment_ID = value; }
        } 
    }
 

            
            public ObservableCollection<CustomAppointment> appointmentCollection { get ; set; }
     
           public ScheduleViewModel()
           {
            CustomAppointment  scheduleAppointment = new CustomAppointment();
            scheduleAppointment.Subject = "Meeting";            scheduleAppointment.AppointmentID = "579";
            scheduleAppointment.Color = Color.Green;
            scheduleAppointment.StartTime = DateTime.Now.Date.AddHours(10);
            scheduleAppointment.EndTime = DateTime.Now.Date.AddHours(12);
            AppointmentCollection = new ObservableCollection<CustomAppointment>();
            AppointmentCollection.Add(scheduleAppointment);
           } 
   
 

  
     <syncfusion:SfSchedule
       x:Name="schedule" ScheduleView="WeekView" 
       DataSource = "{Binding AppointmentCollection}" 
       HorizontalOptions="FillAndExpand"  
       VerticalOptions="FillAndExpand" >
      </syncfusion:SfSchedule>
 

            
         schedule.CellTapped += CellTappedEventHandler;
 
        void CellTappedEventHandler(object sender, CellTappedEventArgs e)
        {
           var appointment = e.Appointment as CustomAppointment;
           if(appointment != null && appointment.Subject == "Meeting")
                DisplayAlert("Appointment details", appointment.AppointmentID, "ok");
        }