Extension methods must be defined in a non-generic static class

Add keyword static to class declaration:

// this is a non-generic static class
public static class LinqHelper
{
}

if you do not intend to have static functions just get rid of the "this" keyword in the arguments.

A work-around for people who are experiencing a bug like Nathan:

The on-the-fly compiler seems to have a problem with this Extension Method error... adding static didn't help me either.

I'd like to know what causes the bug?

But the work-around is to write a new Extension class (not nested) even in same file and re-build.

Figured that this thread is getting enough views that it's worth passing on (the limited) solution I found. Most people probably tried adding 'static' before google-ing for a solution! and I didn't see this work-around fix anywhere else.

change

public class LinqHelper

to

public static class LinqHelper

Following points need to be considered when creating an extension method:

1. The class which defines an extension method must be non-generic, static and non-nested
2. Every extension method must be a static method
3. The first parameter of the extension method should use the this keyword.