Error: Object Reference is not set to an instance of object

Question

I'm currently developing an application that will give user capability of downloading demo software from link provided by us in his email address. After 24 hours, now I have done through link shown in his email address, and he can download but in the coding of disable of this link .. I'm getting error my code is ..

protected void btn_sub_Click(object sender, EventArgs e)
{        
    cn.Open();
    objInquiry.Name = txt_name.Text.ToString().Trim();
    objInquiry.MobileNo = txtMobileNo.Text.ToString().Trim();
    objInquiry.EmailId = txt_eid.Text.ToString().Trim();
    objInquiry.InquiryFor = "Agriculture Product Marketing comity System".ToString().Trim();
    objInquiry.Message = txt_msg.Text.ToString().Trim();

    using (DataSet ds = objInquiry.InsertInquiry())
    {
        Msg.Visible = true;
        Msg.Text = "Thank U For Inquiry We Will Send Demo Link To Your Email Please Check Your Email Regularly";
    }

    try
    {
        DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString());
        DateTime dt2 = DateTime.Now;
        TimeSpan ts = dt2 - dt1;

        if (ts.TotalMinutes > 5)
        {
            Response.Write("Download time is over");
        }
        else
        {
            MailMessage mail = new MailMessage();
            mail.From = new MailAddress("abc@gmail.com");
            mail.To.Add(txt_eid.Text);
            mail.Subject = txtInquiryFor.Text;
            mail.IsBodyHtml = true;
            mail.Body = "Welcome Mr." + txt_name.Text + "<br><br>";
            mail.Body += "To ShreeHans Webnology" + "<br><br>";
            mail.Body += "Thank u for putting inquiry for" + txtInquiryFor.Text + "<br><br>";
            mail.Body += "Please Click on Following Link To Download Your Demo" + "<br><br>";
            mail.Body += "<a href=\"http://www.test.co.in/ConatctUs.aspx?period=" + DateTime.Now + "'\">Download Demo Software</a>";

            SmtpClient smtp = new SmtpClient();
            smtp.Host = "smtp.gmail.com";
            smtp.Port = 587;
            smtp.EnableSsl = true;
            smtp.Credentials = new System.Net.NetworkCredential("abc@gmail.com", "*****");
            smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
            smtp.Send(mail);
        }
    }
    catch (Exception ex)
    {
        ex.ToString();
    }

DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString()); — purvang pandya, Apr 08 '13 at 10:19
And yet again, Definitive answer: [What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net/4660186#4660186). — Grant Thomas, Apr 08 '13 at 10:22

score 2 · Answer 1 · answered Apr 08 '13 at 10:22

As you have mentioned that the error is in the line

DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString());

So it suggest that you have null value in

Request.QueryString["period"].ToString()

First check for null value then convert it to date time

if(Request.QueryString["period"]!=null)
{
    DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString());
}

score 1 · Answer 2 · answered Apr 08 '13 at 10:20

1

Probably Request.QueryString["period"] is null so when calling ToString() on it, you would get the Object Reference not set to an instance of an object exception.

Check for a null reference before calling ToString:

var period = Request.QueryString["period"];
if (period != null) {
    DateTime dt1 = Convert.ToDateTime(period.ToString());
}

answered Apr 08 '13 at 10:20

Andreas Grech

105,982
98
297
360

so what should be the solution how i can fill that null value ? – purvang pandya Apr 08 '13 at 10:24
Since it's the querystring, that value should be in your url: `/index.html?period=whatever`. – Andreas Grech Apr 08 '13 at 10:25

score 1 · Answer 3 · answered Apr 08 '13 at 10:21

1

Check if that parameter is there in your QueryString.

TimeSpan ts;
if(null != Request.QueryString["period"])
{
  DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString());
  DateTime dt2 = DateTime.Now;
  TimeSpan ts = dt2 - dt1;
}

answered Apr 08 '13 at 10:21

nunespascal

17,584
2
43
46

score 1 · Answer 4 · answered Apr 08 '13 at 10:22

If DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString()) is throwing error then than means you don't have period in your querystring. Better to check

if(Request.QueryString["period"]!=null)
{
  DateTime dt1 = Convert.ToDateTime(Request.QueryString["period"].ToString());
 . .
 . .
}

Error: Object Reference is not set to an instance of object

4 Answers4