Btukfyl

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;



/// <summary>

/// Helper methods for link

/// </summary>

public class LinqHelper

{

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)

    {

        return ApplyOrder<T>(source, property, "OrderBy");

    }

    public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)

    {

        return ApplyOrder<T>(source, property, "OrderByDescending");

    }

    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)

    {

        return ApplyOrder<T>(source, property, "ThenBy");

    }

    public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)

    {

        return ApplyOrder<T>(source, property, "ThenByDescending");

    }

    static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> 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<,>).MakeGenericType(typeof(T), type);

        LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);



        object result = typeof(Queryable).GetMethods().Single(

                method => method.Name == methodName

                        && method.IsGenericMethodDefinition

                        && method.GetGenericArguments().Length == 2

                        && method.GetParameters().Length == 2)

                .MakeGenericMethod(typeof(T), type)

                .Invoke(null, new object { source, lambda });

        return (IOrderedQueryable<T>)result;

    }

}

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.

Add keyword static to class declaration:

// this is a non-generic static class

public static class LinqHelper

{

}

Change it to

public static class LinqHelper

Try changing

public class LinqHelper

to

 public static class LinqHelper

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.

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 > Int32.MaxValue ? Int32.MaxValue : Convert.ToInt32(stream.Length);

            Byte buffer = new Byte[length];

            stream.Read(buffer, 0, length);

            return buffer;

        }



    }

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