private void ApplyFilter(string filterText)
        {
            if (Entities == null)
            {
                return;
            }

            if (string.IsNullOrEmpty(filterText))
            {
                DisApplyFilter();
                return;
            }

            FilteredEntities.Clear();

            foreach (var entity in Entities)
            {
                if (entity.Title.Contains(filterText) || (!string.IsNullOrEmpty(entity.FirstName) && entity.LastName.Contains(filterText)))
                {
                    if (!FilteredEntities.Contains(entity))
                    {
                        FilteredEntities.Add(entity);
                    }
                }
            }
            //throw new NotImplementedException();
        }
        private void DisApplyFilter()
        {
            FilteredEntities.Clear();

            foreach (var entity in Entities)
            {
                FilteredEntities.Add(entity);
            }

            IsFilterApplied = false;
        }