高手瞧瞧，这是为什么错？

Question

错误提示：未将对象引用设置到对象的实例（就是这一行：string news_id = Request.QueryString["news_id"].ToString();）
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.Sql;
using System.Data.SqlClient;public partial class manage_News_datail : System.Web.UI.Page
{    public string News_title = "";
    public string News_zuozhe = "新闻作者：";
    public string News_neirong = "";
    public string News_AddDatetime = "录入时间:";
    public string pre_News = "";
    public string next_News = "";
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string news_id = Request.QueryString["news_id"].ToString();
            if (news_id.Trim() == "")
            {
                return;
            }
            DataSet ds = News_GetByID(news_id);            if (ds == null && ds.Tables.Count <= 0 && ds.Tables[0].Rows.Count <= 0)
            {
                return;
            }
            
            AddNewsneirong(ds.Tables[0]);
            AddPreNews(ds.Tables[1]);
            AddNextNews(ds.Tables[2]);
                   }    }    private void AddPreNews(DataTable dt)
    {
        if (dt == null || dt.Rows.Count <= 0)
        {
            pre_News = "呵呵，没有啦！";
            return;
        }
        DataRow dr=dt.Rows[0];
        pre_News = "A  href=News_datail.aspx?news_id=" + dr["id"].ToString() + ">" + dr["News_title"].ToString() + "</A>";    }    private void AddNextNews(DataTable dt)
    {
        if (dt == null || dt.Rows.Count <= 0)
        {
            next_News = "呵呵，没有啦！";
            return;
        }        DataRow dr=dt.Rows[0];        next_News = "A  href=News_datail.aspx?news_id=" + dr["id"].ToString() + ">" + dr["News_title"].ToString() + "</A>";
    }    private void AddNewsneirong(DataTable dt)
    {
        if (dt == null || dt.Rows.Count <= 0)
        {
            return;
        }
        DataRow dr=dt.Rows[0];        this.News_title=dr["News_title"].ToString();
        this.News_zuozhe += dr["News_zuozhe"].ToString();
        this.News_neirong=dr["News_neirong"].ToString();
        this.News_AddDatetime += dr["News_AddDatetime"].ToString();
    }    private DataSet News_GetByID(string news_id)
    {
        SqlConnection conn = new SqlConnection();
        conn.ConnectionString = ConfigurationManager.ConnectionStrings["xiaoxueConnectionString3"].ConnectionString;
        SqlCommand command = new SqlCommand();
        command.CommandText = "News_GetByID";
        command.Connection = conn;
        command.CommandType = CommandType.StoredProcedure;
        SqlParameter parms = new SqlParameter();
        parms.ParameterName = "@intNewsID";
        parms.SqlDbType = SqlDbType.Int;
        parms.Value = news_id;        command.Parameters.Add(parms);        DataSet ds = new DataSet();        try
        {
            SqlDataAdapter da = new SqlDataAdapter(command);
            da.Fill(ds);
            conn.Close();
        }
        catch
        {
            conn.Close();
            return null;
        }        return ds;
    }
    }

Answer 1

string news_id = Request.QueryString["news_id"].ToString();news_id没有值。判断下if(Request.QueryString["news_id"]!=null)
{
string news_id = Request.QueryString["news_id"].ToString();}

Answer 2

传值的时候先判断一下是不是为空
if(Request.QueryString["news_id"].ToString()!="" && Request.QueryString["news_id"]!=null)
string rev= Request.QueryString["news_id"].ToString();这样就不报错了，记得给变量赋初始值

Answer 3

 string news_id = Request.QueryString["news_id"].ToString();
 if (!IsPostBack)
        {

           

Answer 4

Request.QueryString["news_id"]为null,
在进行tostring()的时候，就会提示未将对象引用设置到对象的实例

Answer 5

楼上正解,
你可以这样写 string news_id = "" + Request.QueryString["news_id"];

Answer 6

string news_id = Request.QueryString["news_id"].ToString();

Answer 7

UP~~~传过来的值是空的啊直接ToString就会抛异常了啊 pre_News = "<A  href=News_datail.aspx?news_id

Answer 8

Request.QueryString["news_id"].ToString();
这里没有渠道值，取之前先request判断下

Answer 9

string id=Request.QueryString[ "news_id "]==null?"1":Request.QueryString[ "news_id "];
这样写永远不会错了

Answer 10

QueryString["news_id"] 为空 没有传过来值

Answer 11

string news_id = Request.QueryString["news_id"]??"为null时的默认值";