（转）C# 3.0新特性之LambdaExpressions

LambdaExpressions.cs（Lambda表达式）

using System; 
using System.Data; 
using System.Configuration; 
using System.Linq; 
using System.Web; 
using System.Web.Security; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
using System.Xml.Linq; 
 
using System.Collections.Generic; 
 
/// <summary> 
/// LambdaExpressions（Lambda表达式）的摘要说明 
/// </summary> 
public class LambdaExpressions 
{ 
        public int ID { get; set; } 
        public string Name { get; set; } 
 
        public void LambdaExpressionsTest() 
        { 
                List<LambdaExpressions> list = new List<LambdaExpressions> 
                { 
                        new LambdaExpressions { ID = 1, Name = "webabcd" }, 
                        new LambdaExpressions { ID = 2, Name = "webabcdefg" }, 
                        new LambdaExpressions { ID = 3, Name = "webabcdefghijklmn" } 
                }; 
 
                IEnumerable<LambdaExpressions> l = list.Where(le => le.Name == "webabcd"); 
 
                // 上面的（Lambda表达式）等同于下面的（匿名方法） 
 
                // IEnumerable<LambdaExpressions> l2 = list.Where(delegate(LambdaExpressions le) { return le.Name == "webabcd"; }); 
 
 
 
                // 相关委托 
                // public delegate TResult Func<T, TResult>(T arg); 
            
                // 相关Where扩展方法 
                // Func<TSource, bool>：接受一个类型为TSource的参数 
                // Func<TSource, bool>：某个需要满足的条件，返回bool值 
                // public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) 
                // { 
                //         foreach (TSource item in source) 
                //         { 
                //                 if (predicate(item)) 
                //                 { 
                //                         yield return item; 
                //                 } 
                //         } 
                // } 
                 
        } 
}

QuerySyntax.cs（查询语法）

using System; 
using System.Data; 
using System.Configuration; 
using System.Linq; 
using System.Web; 
using System.Web.Security; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
using System.Xml.Linq; 
 
using System.Collections.Generic; 
 
/// <summary> 
/// QuerySyntax（查询语法）的摘要说明 
/// </summary> 
public class QuerySyntax 
{ 
        public int ID { get; set; } 
        public string Name { get; set; } 
 
        public void QuerySyntaxTest() 
        { 
                List<QuerySyntax> list = new List<QuerySyntax> 
                { 
                        new QuerySyntax { ID = 1, Name = "webabcd" }, 
                        new QuerySyntax { ID = 2, Name = "webabcde" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdef" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefg" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefgh" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefghi" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefghij" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefghijk" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefghijkl" }, 
                        new QuerySyntax { ID = 2, Name = "webabcdefghijklm" }, 
                        new QuerySyntax { ID = 3, Name = "webabcdefghijklmn" } 
                }; 
 
                IEnumerable<QuerySyntax> l = from o in list 
                                                                         where o.Name.Length > 10 
                                                                         orderby o.Name.Length descending 
                                                                         select o; 
 
                // 上面的（查询语法）等同于下面的（LINQ扩展方法和Lambda表达式） 
                // 查询语法相对更容易理解 
 
                // IEnumerable<QuerySyntax> l = list.Where(o => o.Name.Length > 10).OrderByDescending(o => o.Name.Length); 
 
 
 
                // Projection（映射） 
                // 可以返回一个新的类型 
                IEnumerable<Projection> l2 = from o in list 
                                                                            where o.Name.Length > 10 
                                                                            orderby o.Name.Length descending 
                                                                            select new Projection { Name = o.Name }; 
        } 
} 
 
/// <summary> 
/// 为了演示Projection（映射）而写的实体类 
/// </summary> 
public class Projection 
{ 
        public string Name { get; set; } 
}

AnonymousTypes.cs（匿名类型）

using System; 
using System.Data; 
using System.Configuration; 
using System.Linq; 
using System.Web; 
using System.Web.Security; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
using System.Xml.Linq; 
 
using System.Collections.Generic; 
 
/// <summary> 
/// AnonymousTypes（匿名类型）的摘要说明 
/// </summary> 
public class AnonymousTypes 
{ 
        public int ID { get; set; } 
        public string Name { get; set; } 
        public int Age { get; set; } 
 
        public void AnonymousTypesTest() 
        { 
                List<AnonymousTypes> list = new List<AnonymousTypes> 
                { 
                        new AnonymousTypes { ID = 1, Name = "webabcd", Age = 10 }, 
                        new AnonymousTypes { ID = 2, Name = "webabcdefg", Age = 20 }, 
                        new AnonymousTypes { ID = 3, Name = "webabcdefghijklmn", Age = 30 } 
                }; 
 
                // listAnonymousTypes - 匿名类型 
                var listAnonymousTypes = from l in list 
                                                                 where l.Name == "webabcd" 
                                                                 select new { Name = l.Name, Age = l.Age }; 
 
                foreach (var v in listAnonymousTypes) 
                { 
                        // v - 匿名类型，可以在Visual Studio中得到编译时检查和完整的intellisense 
                        string name = v.Name; 
                        int age = v.Age; 
                } 
 
                // 声明匿名类型：将new关键词后面的类型名称省略掉 
                var person = new { Name = "webabcd", Age = 27 }; 
                // person - 匿名类型，可以在Visual Studio中得到编译时检查和完整的intellisense 
                string myName = person.Name; 
                int myAge = person.Age; 
        } 
}

原文链接：

http://www.cnblogs.com/qiuweiguo/archive/2011/08/03/2126588.html