Revit 二次开发—获取特定类别的元素

public static List<Element> GetAllBlocks(Document doc)
        {
            try
            {
                FilteredElementCollector collector = new FilteredElementCollector(doc);
                List<Element> elems = collector.OfClass(typeof(FamilyInstance)).
                    OfCategory(BuiltInCategory.OST_StructuralFraming).
                    ToElements().
                    ToList();
                return elems;
            }
            catch (Exception)
            {

                TaskDialog.Show("Error", "获取到所有节段失败");
                return null;
            }
        }