添加相应的using引用
如:using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.Windows;
using Autodesk.AutoCAD.ApplicationServices;
using AcadApp = Autodesk.AutoCAD.ApplicationServices.Application;