.NET 3.5(4) - C# 3.0新特性之LambdaExpressions（Lambda表达式）

[索引页]
[源码下载]

步步为营VS 2008 + .NET 3.5(4) - C# 3.0新特性之LambdaExpressions（Lambda表达式）、QuerySyntax（查询语法）和AnonymousTypes（匿名类型）

作者：webabcd


介绍
    ·LambdaExpressions（Lambda表达式）
    ·QuerySyntax（查询语法）
    ·AnonymousTypes（匿名类型）


示例
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;
        }
}

 

 

OK
[源码下载]

 

本文出自 “webabcd” 博客，请务必保留此出处http://webabcd.blog.51cto.com/1787395/344994