Get Object Reference Error when trying to use Request.QueryString

Question

I have a page.aspx that reads the query string, and if the QueryString is something like page.aspx?id=1, it runs some code.

However, I want it to simply ignore that code if no QueryString is specified. If I simply go to page.aspx. Right now, the only code I have on page load is

if (Request.QueryString["id"].Equals("1"))
  {
     //Do something
  }

That works if I go to page.aspx?id=1. However, simply going to page.aspx gives me this error:

object reference not set to an instance of an object

How can I load the page with no query string?

Your problem is that you are not also checking for nulls: `Request.QueryString["id"] != "" && Request.QueryString["id"] != null)` — stripthesoul, May 13 '14 at 12:50
Almost all cases of `NullReferenceException` are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, May 13 '14 at 13:05

score 8 · Accepted Answer · answered May 13 '14 at 12:47

8

You need to check for nulls

if (Request.QueryString["id"] != null && Request.QueryString["id"].Equals("1"))
{
   //Do something
}

answered May 13 '14 at 12:47

pbjork

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4
10

Amit Joki · Answer 2 · 2014-05-13T12:53:25.050

3

You can do this:

if(Request.QueryString.Length != 0)
{
   ...
}

If you try to access elements which are not present, you'll receive an exception. So, since QueryString has a property of Length, checking it against 0 means there is no query string at all.

Else if you want to know that only if id key isn't present, you can do this:

if(Request.QueryString.AllKeys.Contains("id"))
{

}

edited May 13 '14 at 12:53

answered May 13 '14 at 12:46

Amit Joki

56,285
7
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IMO it would be better to check if the `QueryString` key is `id` or not also. +1 anyway – Farhad Jabiyev May 13 '14 at 12:48

Sven Grosen · Answer 3 · 2014-05-13T13:04:22.723

1

This will cover any null reference issues or when there simply is an empty query string

if (Request.QueryString != null && Request.QueryString["id"] != null && Request.QueryString["id"] == "1")
{
//do work
}

edited May 13 '14 at 13:04

answered May 13 '14 at 12:47

Sven Grosen

5,547
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that will not compile – Selman Genç May 13 '14 at 12:59
@Selman22 you are right, don't know what I was thinking there, thanks – Sven Grosen May 13 '14 at 13:04

score 1 · Answer 4 · answered May 13 '14 at 12:48

1

Try this:

if (Request.QueryString["id"] != null && Request.QueryString["id"].Equals("1"))
{
 //Do something
}

Another way :

string id = Request.QueryString["id"] ?? "";
if(id == "1")
{
     //Do something
}

answered May 13 '14 at 12:48

Ranjan Kumar

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Ramy M. Mousa · Answer 5 · 2014-05-13T13:37:00.280

0

Whenever you see this error :

     object reference not set to an instance of an object

Know that you are checking for something that is null or simply doesn't exist

so try this :

    if(Request.QueryString["id"] != null)
     {
        if (Request.QueryString["id"].Equals("1"))
        {
               //Do something
        }
     }

edited May 13 '14 at 13:37

answered May 13 '14 at 12:49

Ramy M. Mousa

5,301
3
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`Request.QueryString.Length` will never be `null`, I guess. – Bharadwaj May 13 '14 at 12:58
And what if there is a `QueryString` value exists and its not `id`? – Bharadwaj May 13 '14 at 13:00
if the ID is always an int so you can use int.TryParse(Request.QueryString["whatever"]) then if it returns true , then it's an id which you can use – Ramy M. Mousa May 13 '14 at 13:15
1

`Request.QueryString.Length` will return `int`, so the default value will always be 0 (if no query string exists). And if there is a query string, there is no guaranty that it should be `"id"`. – Bharadwaj May 13 '14 at 13:23
Edited : Ops sorry for that , i added the length property by mistake, sorry – Ramy M. Mousa May 13 '14 at 13:30
But still it can't be predicted that the `QueryString` will be for `"id"`. You need to check for `null` value for `Request.QueryString["id"]` also – Bharadwaj May 13 '14 at 13:32
flu makes more than that :D you're totally true , sorry for that – Ramy M. Mousa May 13 '14 at 13:37
Now this works fine :) – Bharadwaj May 13 '14 at 13:38

Get Object Reference Error when trying to use Request.QueryString

5 Answers5