internal static FrameworkElement GetExpandSite(Expander expander) { if (expander is null) { return(null); } var expandSite = GetExpandSiteControl(expander); if (expandSite is null) { expander.ApplyTemplate(); expandSite = expander.Template?.FindName("ExpandSite", expander) as FrameworkElement; SetExpandSiteControl(expander, expandSite); } return(expandSite); }