Question

我正在尝试搜索我的数据库以检索一些结果并将其填充到gridview中。

然而，我在标题中得到了上述错误，并且一些研究并没有真正帮助我解决为什么这种错误标记，并且想知道是否有更敏锐的人能够解释这个错误的原因。我的特定页面代码隐藏文件的代码如下所示：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

namespace StarksComics
{
    public partial class search : System.Web.UI.Page
    {

        SqlConnection con = new SqlConnection();
        string b = "";


        protected void Page_Load(object sender, EventArgs e)
        {
            con.ConnectionString = ConfigurationManager.ConnectionStrings["DBVS"].ConnectionString; // the error occurs at this line. ---- nullreference exception was unhandled by code.

            if (con.State == ConnectionState.Closed)
            {
                con.Open();
            }

        }

        private void user_chk()
        {
            string a;
            a = TextBox1.Text;

            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "select * from tbCharacters where CharName like'" + a + "%'";
            cmd.Connection = con;

            SqlDataReader dr;
            dr = cmd.ExecuteReader();
            if (dr.HasRows)
            {
                dr.Read();
                rep_bind();
                GridView1.Visible = true;

                TextBox1.Text = "";

            }
            else
            {
                GridView1.Visible = false;
                b = TextBox1.Text + "is not available in list";
                TextBox1.Text="";
            }
        }

        private void rep_bind()
        {
            string a;
            a = TextBox1.Text;
            SqlDataAdapter adp = new SqlDataAdapter("select * from tbCharacters where CharName like'" + a + "%'",
                ConfigurationManager.ConnectionStrings["DBVS"].ConnectionString);
            DataSet ds = new DataSet();
            adp.Fill(ds);
            GridView1.DataSource = ds;
            GridView1.DataBind();
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            user_chk();
        }
    }

}

再一次，非常感谢您审核我的代码。（我已经注释掉了这行，除非你在页面加载方法中拖动栏，否则它是不可见的。）

Answer 1

显然它无法找到连接字符串DBVS。

检查web.config是否存在。

尝试使用此代码检查连接是否为null：

ConnectionString connStr = ConfigurationManager.ConnectionStrings["DBVS"];

if (connStr == null)
{
    throw new Exception("Cannot find connection string DBVS in web.config");
}

运行webform时，对象引用未设置为对象错误标志的实例

1 个答案: