Display checked checkbox items in repeater

Question

Here is my code I m getting  error in if(ch.Checked)  plz fix it:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

 

 

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Configuration;

using System.Data.SqlClient;

using System.Data;

public partial class Assg1DatalistCheckbox : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

if (Page.IsPostBack == false)

{

ChkDataList_Bind();

}

}

private void ChkDataList_Bind()

{

SqlDataAdapter adp = new SqlDataAdapter("Select * from tbbook", ConfigurationManager.ConnectionStrings["cn"].ConnectionString);

DataSet ds = new DataSet();

adp.Fill(ds);

DataList1.DataSource = ds;

DataList1.DataBind();

}

 

 

protected void Button1_Click(object sender, EventArgs e)

{

String d = " ";

for(Int32 i = 0; i < DataList1.Items.Count; i++)

{

CheckBox ch;

ch = (CheckBox)(DataList1.Items[i].FindControl("chk"));

if(ch.Checked)

{

// concatenating

d += DataList1.DataKeys[i].ToString() + ",";

}

}

d = d.Substring(0, d.Length - 1);

String qry = "Select * from tbbook where BookId in(" + d + ")";

SqlDataAdapter adp = new SqlDataAdapter(qry, ConfigurationManager.ConnectionStrings["cn"].ConnectionString);

DataSet ds = new DataSet();

adp.Fill(ds);

Repeater1.DataSource = ds;

Repeater1.DataBind();

}

}