我收到錯誤消息：擴(kuò)展方法必須在非通用靜態(tài)類中定義在線上：public class LinqHelper這是基于Mark Gavells代碼的幫助程序類。我對這個錯誤的含義感到非常困惑，因為我確信當(dāng)我在星期五離開它時，它可以正常工作！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);