How to solve 'Extension method must be defined in a non-generic static class'?

Question

Im pretty new to C# and got myself a project from a friend and I'm having this error when I'm trying to compile it:

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

The code looks like this:

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

Probably a very simple problem but I cant figure it out.

Is your intention to add an extension method or by mistake you added this keyword in method parameter? If latter, just drop the this keyword from parameter, if former then [do what compiler says](http://stackoverflow.com/questions/6096299/extension-methods-must-be-defined-in-a-non-generic-static-class) — Sriram Sakthivel, Oct 28 '14 at 08:42

score 0 · Answer 1 · answered Oct 28 '14 at 08:37

You're probably trying to define an extension method in that class.

An extension method is marked with the static modifier and its first argument with the this modifier, e.g.:

public static void Method(this string arg) {}

If you added the this modifier by mistake, simply remove it to make it a normal static method. If you did it on purpose, move the method declaration to a static non-generic non-nested class.

score 0 · Answer 2 · answered Oct 28 '14 at 08:38

Well, it's telling you exactly what's wrong - you can't put an extension method (a static method whose first parameter is preceded by this) in anything other than a non-generic static class. Look for a method (or methods) where the first parameter is preceded by this, and move them to a new, non-generic static class:

public static class SomeExtensions
{
    // Extension methods go here, e.g.
    public static void SomeMethod(this SomeClass firstParam, int secondParam)
    {
        // ...
    }
}

score 0 · Answer 3 · answered Oct 28 '14 at 08:38

You are using the this keyword in a method signature, indicating it is an extension method.

You should create a static class to contain those methods. The signature must be something like this:

public static class PageExtensionMethods
{
    public static void SomeMethod(this SomeType s)
    { }
}

Make sure though, you really intent to use extension methods. If it is just a method you want to call, it doesn't really have to be an extension method. Remove the this keyword then.

Dmitry Bychenko · Answer 4 · 2014-10-28T08:45:25.283

0

Just do as complier wants it should be done:

  // Public static non generic class (exactly what compiler wants)
  public static class PageExtensions {
    ...
    // Your extension method for System.Web.UI.Page
    public static void MyExtensionMethod(this System.Web.UI.Page value) {
      ...
    }
  }

edited Oct 28 '14 at 08:45

answered Oct 28 '14 at 08:38

Dmitry Bychenko

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How to solve 'Extension method must be defined in a non-generic static class'?

4 Answers4