NullreferenceException was unhandled by user code :Object reference not set to an instance of an object

Question

User-1393440807 posted

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();

}
}
}

Answer 1

User1208776063 posted

I'm not an expert in devExpress, but here is what I suggest. 

dps2305

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

Delete above line and set Checkbox value to HouseImageID in markup as value='<%# Eval("HouseImageID") %>'. So, that will bind the value and you retrieve the value as

dps2305

com.Parameters.AddWithValue("@HouseImageID", cid);

com.Parameters.AddWithValue("@HouseImageID", chkStatus.Value);

Answer 2

User281315223 posted

It's important to always check within code to see if a possibly null value exists to avoid exceptions like these as this occured because you attempted to use the ToString() method on a null object. 

// Grab your House Image (if possible)
var houseImage = row.EvalDataItem("HouseImageID");

// Check if it exists
if(houseImage != null)
{
    // If so, then store the appropriate value you needed
    string cid = houseImage.ToString();
}
else
{
    // It didn't exist and would have thrown an error otherwise
}