public new WeekPlannerItem Add(WeekPlannerItem item)
 {
     base.Add(item);
     if (_calendar != null)
     {
         item.Calendar = _calendar;
         _calendar.ResetLayers();
         _calendar.Invalidate();
     }
     return(item);
 }
        public new void Remove(int rowIndex)
        {
            var row = this.ElementAt(rowIndex);

            _calendar.ResetLayers();

            base.Remove(row);
            ClearRowIndex();
            _calendar.Invalidate();
        }