private void MenuItem_Click_ContactsAddToGroup(object sender, RoutedEventArgs e) { TreeViewItem selectedTreeViewItem = treeView.SelectedItem as TreeViewItem; Person selectedPerson = selectedTreeViewItem.Tag as Person; TreeViewItem parentTreeViewItem = selectedTreeViewItem.Parent as TreeViewItem; Group curGroup = parentTreeViewItem.Tag as Group; ModifyGroupWindow modifyGroupWindow = new ModifyGroupWindow(ref services, ref curGroup, ref selectedPerson, ModifyGroupMode.Add); modifyGroupWindow.ShowDialog(); LoadData(services.GetGroups()); }