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

Question

I m getting the error      Extension methods must be defined in a non-generic static class   On the line   public class LinqHelper   Here is the helper class  based on Mark Gavells code   I m really confused as to what this error means as I am sure it was working fine when I left it on Friday   using System  using System Collections Generic  using System Linq  using System Web  using System Linq Expressions  using System Reflection        lt summary gt      Helper methods for link      lt  summary gt  public class LinqHelper       public static IOrderedQueryable lt T gt  OrderBy lt T gt  this IQueryable lt T gt  source  string property                return ApplyOrder lt T gt  source  property   OrderBy              public static IOrderedQueryable lt T gt  OrderByDescending lt T gt  this IQueryable lt T gt  source  string property                return ApplyOrder lt T gt  source  property   OrderByDescending              public static IOrderedQueryable lt T gt  ThenBy lt T gt  this IOrderedQueryable lt T gt  source  string property                return ApplyOrder lt T gt  source  property   ThenBy              public static IOrderedQueryable lt T gt  ThenByDescending lt T gt  this IOrderedQueryable lt T gt  source  string property                return ApplyOrder lt T gt  source  property   ThenByDescending              static IOrderedQueryable lt T gt  ApplyOrder lt T gt  IQueryable lt T gt  source  string property  string methodName                string   props   property Split               Type type   typeof T           ParameterExpression arg   Expression Parameter type   x            Expression expr   arg          foreach  string prop in props                           use reflection  not ComponentModel  to mirror LINQ             PropertyInfo pi   type GetProperty prop               expr   Expression Property expr  pi               type   pi PropertyType                    Type delegateType   typeof Func lt   gt   MakeGenericType typeof T   type           LambdaExpression lambda   Expression Lambda delegateType  expr  arg            object result   typeof Queryable  GetMethods   Single                  method   gt  method Name    methodName                          amp  amp  method IsGenericMethodDefinition                          amp  amp  method GetGenericArguments   Length    2                          amp  amp  method GetParameters   Length    2                   MakeGenericMethod typeof T   type                   Invoke null  new object     source  lambda             return  IOrderedQueryable lt T gt  result

User · Accepted Answer

change   public class LinqHelper   to   public static class LinqHelper   Following points need to be considered when creating an extension method    The class which defines an extension method must be non-generic  static and non-nested Every extension method must be a static method The first parameter of the extension method should use the this keyword

User · Answer

Change it to  public static class LinqHelper

User · Answer

Try changing   public class LinqHelper   to   public static class LinqHelper

User · Answer

I encountered a similar issue  I created a  foo  folder and created a  class  inside foo  then I get the aforementioned error  One fix is to add  static  as earlier mentioned to the class which will be  public static class LinqHelper     My assumption is that when you create a class inside the foo folder it regards it as an extension class  hence the following inter alia rule apply to it   1  Every extension method must be a static method  WORKAROUND If you don t want static  My workaround was to create a class directly under the namespace and then drag it to the  foo  folder

User · Answer

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

User · Answer

Extension method should be inside a static class  So please add your extension method inside a static class   so for example it should be like this  public static class myclass               public static Byte   ToByteArray this Stream stream                        Int32 length   stream Length  gt  Int32 MaxValue   Int32 MaxValue   Convert ToInt32 stream Length               Byte   buffer   new Byte length               stream Read buffer  0  length               return buffer

User · Answer

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

User · Answer

I was scratching my head with this compiler error  My class was not an extension method  was working perfectly since months and needed to stay non-static  I had included a new method inside the class  private static string TrimNL this string Value         I had copied the method from a sample and didn t notice the  quot this quot  modifier in the method signature  which is used in extension methods  Removing it solved the issue

User · Answer

Try changing it to static class and back  That might resolve visual studio complaining when it s a false positive

User · Answer

Add keyword static to class declaration      this is a non-generic static class public static class LinqHelper

[c#] Extension methods must be defined in a non-generic static class

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