MODEMACRO：系统变量->字符型->在状态行显示字符串
    Cad设置左下角的状态栏：

    1. Autodesk.AutoCAD.ApplicationServices.Application.SetSystemVariable("MODEMACRO","这是状态栏");

    Cad获取左下角的状态栏：

    1. Autodesk.AutoCAD.ApplicationServices.Application.GetSystemVariable("MODEMACRO");