这段代码提示未将对象引用设置到对象的实例，为什么？

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace 二级列表页
{
public partial class shoppingCart : System.Web.UI.Page
{

    protected void Page_Load(object sender, EventArgs e)
    {

        //加载COOKIE
        if (Request.Cookies["CartBookInfo"] != null)
        {
            if (Request.Cookies["CartBookInfo"].Value != null)
            {
                string currentCartBookInfo = Request.Cookies["CartBookInfo"].Value;
                string[] bookinfo_strings = currentCartBookInfo.Split(',');
                //加载购物车现有的书籍信息
                for (int i = 0; i < bookinfo_strings.Length; i = i + 2)
                {
                    ListItem li = new ListItem(bookinfo_strings[i], bookinfo_strings[i + 1]);
                    lstCartBook.Items.Add(li);

                }
            }
        }

string BookName = Request["BookName"].ToString();
string ISBN = Request["ISBN"].ToString();
lstCartBook.Items.Add(new ListItem(BookName, ISBN));

        //新加入的书放入cookie保存
        string bookinfo = BookName + "," + ISBN;

        if (Request.Cookies["CartBookInfo"] != null) //不是第一次进入购物车
        {

            string old_bookinfo = Request.Cookies["CartBookInfo"].Value.ToString();
            bookinfo = old_bookinfo + "," + bookinfo;
            Response.Cookies.Remove("CartBookInfo");
            HttpCookie ck = new HttpCookie("CartBookInfo", bookinfo);
            Response.Cookies.Add(ck);

        }
        else //新建COOKIE发回客户端保存
        {
            HttpCookie ck = new HttpCookie("CartBookInfo", bookinfo);
            Response.Cookies.Add(ck);
        }

    }
}

}

Answer 1

首先看哪一行报错，你这里有很多参数、表单、cookie，都有可能取不到值。先搞清楚是哪一个。