查找ListBox的ItemsPanel
ItemsPresenter presenter = (ItemsPresenter)lb.Template.FindName("PART_Presenter", lb);
Panel panel
= (Panel)VisualTreeHelper.GetChild(presenter, 0);
ItemsPresenter presenter = (ItemsPresenter)lb.Template.FindName("PART_Presenter", lb);
Panel panel
= (Panel)VisualTreeHelper.GetChild(presenter, 0);