用户代码未对NullreferenceException进行处理：未将对象引用设置为对象的实例 [英] NullreferenceException was unhandled by user code :Object reference not set to an instance of an object

问题描述

您好，

我正在开发一个小项目并使用devexpress工具。我没有得到正确的代码来获取我的代码中的列值。请帮助我



此处出错：string cid = row.EvalDataItem（HouseImageID）。ToString（）;

Hi There,
I am working a small project and using devexpress tool.I am not getting correct code to get the value of a column in my code.Please,help me

Error here: string cid = row.EvalDataItem("HouseImageID").ToString();

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using BuckshawObjects.Global;
using BuckshawObjects.Objects;
using DevExpress.Web.ASPxEditors;
using System.IO;
using DevExpress.Web.ASPxDataView;
using System.Collections;
using DevExpress.Web.ASPxGridView;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using DevExpress.XtraRichEdit.API.Native;
using System.Drawing;


namespace Buckshaw.Backend
{
    public partial class WebForm5 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }
        public void chkStatus_OnCheckedChanged(object sender, EventArgs e)
        {
            string constr = ConfigurationManager.ConnectionStrings["BuckshawHomesConnectionString"].ConnectionString;

            ASPxCheckBox chkStatus = (ASPxCheckBox)sender;
            //ASPxDataView row = (ASPxDataView)chkStatus.NamingContainer;
            DataViewItemTemplateContainer row=(DataViewItemTemplateContainer)chkStatus.NamingContainer;
            //string cid = row.Controls[0].ToString();
            //string cod =(row.ItemIndex+1).ToString();
            //string cod = row.ItemIndex.ToString();
            //string cod = dataView.FindControl("HouseImageID").ToString();
     
            //string cid = dataView.Controls[0].ToString();
            //string cod = dataView.Items[0].DataItem.ToString();
            string cid = row.EvalDataItem("HouseImageID").ToString();
            //string cid = "True";
            bool status = chkStatus.Checked;
           
            
            string query = "UPDATE [tblHouseImage] SET Active = @Approved WHERE HouseImageID = @HouseImageID";
            //WHERE HouseImageID = @HouseImageID"
            SqlConnection con = new SqlConnection(constr);
            SqlCommand com = new SqlCommand(query, con);
            com.Parameters.AddWithValue("@Approved", status);
            com.Parameters.AddWithValue("@HouseImageID", cid);
            con.Open();
            com.ExecuteNonQuery();
            con.Close();
           dataView.DataBind();

           
       
        }
    }
}

推荐答案

如果查看文档： HTTPS ：//help.devexpress.com/#AspNet/DevExpressWebASPxClassesItemTemplateContainerBase_EvalDataItemtopic [ ^ ]你会看到EvalDataItme的参数是一个表达式 - 所以有可能它需要更多的东西，比如

If you look at the documentation: https://help.devexpress.com/#AspNet/DevExpressWebASPxClassesItemTemplateContainerBase_EvalDataItemtopic[^] you will see that the parameter to EvalDataItme is an Expression - so the chances are that it wants somethign a little more like

HouseImageId=666

比

Than

HouseImageId

作为参数......

as a parameter...

这篇关于用户代码未对NullreferenceException进行处理：未将对象引用设置为对象的实例的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！