NullReferenceException retrieving value from known Request.Form[key] elements in C#

Question

I am trying to retrieve the values from a number of RadioButtonGroups on PostBack using the Request.Form keys like so:

string val = Request.Form["ControlName" + i].ToString();

But I keep getting a NullReferenceException.

I know the keys are a part of the collection, and if I replace the above code with:

Response.Write(Request.Form["RadioGroup" + i].ToString())

The value is displayed on the page.

Why does it throw a NullReferenceException if I try to assign it to a variable, but not when I write it to the browser?

Thanks

Answer 1

The reason why the second one works is probably because you changed the string from "ControlName" to "RadioGroup" .

In order to avoid the NullReferenceException you should avoid calling ToString . The indexer already returns a string so the call to ToString is unnecessary.