private void CheckBox_Click(object sender, RoutedEventArgs e)
 {
     if ((sender as CheckBox).IsChecked == true)
     {
         IViewModel viewModel = DataContext as IViewModel;
         if (viewModel != null)
         {
             viewModel.CheckPermission((grdPermissions.SelectedItem as PermissionItemClass).Identifier);
         }
         ;
     }
     else
     {
         IViewModel viewModel = DataContext as IViewModel;
         if (viewModel != null)
         {
             viewModel.UnCheckPermission((grdPermissions.SelectedItem as PermissionItemClass).Identifier);
         }
         ;
     }
 }