解决ashx文件下的Session“未将对象引用设置到对象的实例”

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using PPT_DAL;
 namespace PPT_Web.tool
 {
     /// <summary>
     /// Login 的摘要说明
     /// </summary>
     public class Login : IHttpHandler
     {
 
         public void ProcessRequest(HttpContext context)
         {
             context.Response.ContentType = "text/html";
             string lo_usm = context.Request.Params["lo_usm"];
             string lo_pwd = context.Request.Params["lo_pwd"];
             UserEntity userModel = PPT_BLL.UserManager.Login(lo_usm,lo_pwd);
             if (userModel != null)
             {
                 context.Session["UserId"] = userModel.USR_ID;
                 context.Response.Write("{'result':'1'}");
             }
             else
             {
                 context.Response.Write("{'result':'0'}");
             }
         }
 
         public bool IsReusable
         {
             get
             {
                 return false;
             }
         }
     }
 }

问题：

　　如题所示，在一般处理程序文件，即ashx文件下调用Session["UserId"],当调试的时候会显示“未将对象实例化的”的错误

解决方法：

　　将该类实现“IRequiresSessionState”的接口即可，而此接口在System.Web.SessionState命名空间下，所以要在上面添加一句：using System.Web.SessionState;

　　最终实现代码如下：

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using PPT_DAL;
 using System.Web.SessionState;
 namespace PPT_Web.tool
 {
     /// <summary>
     /// Login 的摘要说明
     /// </summary>
     public class Login : IHttpHandler, IRequiresSessionState
     {
 
         public void ProcessRequest(HttpContext context)
         {
             context.Response.ContentType = "text/html";
             string lo_usm = context.Request.Params["lo_usm"];
             string lo_pwd = context.Request.Params["lo_pwd"];
             UserEntity userModel = PPT_BLL.UserManager.Login(lo_usm,lo_pwd);
             if (userModel != null)
             {
                 context.Session["UserId"] = userModel.USR_ID;
                 context.Response.Write("{'result':'1'}");
             }
             else
             {
                 context.Response.Write("{'result':'0'}");
             }
         }
 
         public bool IsReusable
         {
             get
             {
                 return false;
             }
         }
     }
 }