Hey Friends..plz help me out...

User 10281574

Hey friends...I am creating an online examination project...I have made the login...the admin part and even all the databse thing is done...but in the user side as i press the start exam button it givving "Object reference not set to an instance of an object. " error...please help me out ASAP...m about to meet the deadlines..and if i meet it i ll be dead... here's my code..

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Instruction : System.Web.UI.Page
{

OnlineExamsDataContext \_mycontext = new OnlineExamsDataContext();
string username;

protected void Page\_Load(object sender, EventArgs e)
{
    **username = Request.QueryString\["username"\].ToString();**
    lbluname.Text = "Welcome   :" + username;
    lbldate.Text = System.DateTime.Now.ToString();


}
protected void btnstart\_Click(object sender, EventArgs e)
{
    int emailid;
    emailid = \_mycontext.ExamTableInsert (Convert.ToDateTime (System.DateTime.Now.ToShortDateString()), Convert.ToInt32 (Request.QueryString\["UserID"\].ToString()), Convert.ToDecimal("0.0"));
    Response.Redirect("QuestionPaper.aspx");

}
protected void lbtnresult\_Click(object sender, EventArgs e)
{
    Response.Redirect("Examresult.aspx");

}

}

User 10281574

it says Object reference not set to an instance of an object. is in the line which i have underlined....:'(

Blikkies

Hey, Make sure your query string "username" exists. You are getting this error because you are trying to convert the a query string that is null to a string. best is to add an if statement:

if (Request.QueryString["username"] != null) {
username = Request.QueryString["username"].ToString();
lbluname.Text = "Welcome :" + username;
lbldate.Text = System.DateTime.Now.ToString();
} else {

//TODO
}

ais07

It is always best practice to convert object with Convert.ToString(Request.QueryString["username"]) instead of .ToString().Check whether you are getting username value as null.

Life Is Beautiful

Richard Deeming

Since Request.QueryString[key] already returns a string, there's absolutely no need to call either Convert.ToString or .ToString() to convert it to a string.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Richard Deeming

Just drop the .ToString() call - Request.QueryString["username"] already returns a string.

username = Request.QueryString["username"];

You also need to HTML-encode the value before you display it, to avoid cross-site scripting (XSS)[^]:

lbluname.Text = "Welcome :" + HttpUtility.HtmlEncode(username)

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

blachsmith

Object reference not set to an instance of an object. it really means that when you request this page ,you haven't passed a param in the request. why not check the former page which entry this one?

CIKolkataDeveloper

Is the value "username" correctly being passed in the querystring. The statement "Request.QueryString["username"].ToString();" is not getting the value from the querystring hence the error