private void MenuItemWithRadioButtons_Click(object sender, RoutedEventArgs e) { Fluent.MenuItem oMenu = (Fluent.MenuItem)sender; User oUser = (User)oMenu.DataContext; bool bIsInList = UserListSelected.Contains(oUser); if (bIsInList) { UserListSelected.Remove(oUser); } else { UserListSelected.Add(oUser); } oMenu.IsChecked = !bIsInList; }