UIApplication uiApp = commandData.Application;
Autodesk.Revit.ApplicationServices.Application application = uiApp.Application;
UIDocument uiDocument = uiApp.ActiveUIDocument;
Document document = uiDocument.Document;
Selection selection = uiDocument.Selection;
Reference bridgeFace = selection.PickObject(ObjectType.Face, "选面"); //选择面类型
Element face = document.GetElement(bridgeFace); //实体
Face downFace = face.GetGeometryObjectFromReference(bridgeFace) as Face; //
Face pf = downFace as PlanarFace; //这个就是最后的Face面
return Result.Succeeded;