Revit 二次开发 获取选中的对象

领导脑瓜一拍，决定结合Revit开发产品，俺可惨了，两眼一抹黑，在他拍脑袋前，俺连Revit是什么、干嘛用的都不知道，硬着头皮上吧。老了，脑瓜不好使了，学过的在这里做个笔记

//获取选中对象

[TransactionAttribute(Autodesk.Revit.Attributes.TransactionMode.Manual)]
public class getSelectEle : IExternalCommand
{

    public Result Execute(ExternalCommandData commandData, ref string messages, ElementSet elements)
    {
          GetSelectionElement(commandData, elements);
           return Result.Succeeded;
    }


    public void GetSelectionElement(ExternalCommandData   commandData, ElementSet elements)
    {
        UIApplication app = commandData.Application;
        Selection sel = app.ActiveUIDocument.Selection;
        ElementSet es = sel.Elements;
        if (es.Size > 0)
        {
            string seleStr = "";
            foreach (Element selitem in es)
            {
                seleStr += selitem.Id + "," + selitem.Name + "\n";
            }  
            TaskDialog.Show("all Selection", seleStr);
        }

     } 
}