public void EditListItems() { List <IWidget> list = new List <IWidget>(); list.Add(IWidget); StoreOldItems(); EditListWindow win = new EditListWindow(list); win.Owner = Application.Current.MainWindow; bool?bRValue = win.ShowDialog(); if ((bool)bRValue) { LoadList(); EditListCommand cmd = new EditListCommand(this, OldItems, IWidget.Items); CurrentUndoManager.Push(cmd); ClearOldItems(); } }