步步為營VS 2008 + .NET 3.5(4) - C# 3.0新特性之LambdaExpressions（Lambda表達式）

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步步為營VS 2008 + .NET 3.5(4) - C# 3.0新特性之LambdaExpressions（Lambda表達式）、QuerySyntax（查詢文法）和AnonymousTypes（匿名類型）

作者：webabcd

介紹

    ·LambdaExpressions（Lambda表達式）

    ·QuerySyntax（查詢文法）

    ·AnonymousTypes（匿名類型）

示例

LambdaExpressions.cs（Lambda表達式）

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表達式）的摘要說明

/// </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表達式）等同于下面的（匿名方法）

                // IEnumerable<LambdaExpressions> l2 = list.Where(delegate(LambdaExpressions le) { return le.Name == "webabcd"; });

                // 相關委托

                // public delegate TResult Func<T, TResult>(T arg);

                // 相關Where擴充方法

                // Func<TSource, bool>：接受一個類型為TSource的參數

                // Func<TSource, bool>：某個需要滿足的條件，傳回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（查詢文法）

/// QuerySyntax（查詢文法）的摘要說明

public class QuerySyntax

        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（查詢文法）等同于下面的（LINQ擴充方法和Lambda表達式）

                // 查詢文法相對更容易了解

                // IEnumerable<QuerySyntax> l = list.Where(o => o.Name.Length > 10).OrderByDescending(o => o.Name.Length);

                // Projection（映射）

                // 可以傳回一個新的類型

                IEnumerable<Projection> l2 = from o in list

                                                                            where o.Name.Length > 10

                                                                            orderby o.Name.Length descending

                                                                            select new Projection { Name = o.Name };

}

/// 為了示範Projection（映射）而寫的實體類

public class Projection

AnonymousTypes.cs（匿名類型）

/// AnonymousTypes（匿名類型）的摘要說明

public class AnonymousTypes

        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 - 匿名類型

                var listAnonymousTypes = from l in list

                                                                 where l.Name == "webabcd"

                                                                 select new { Name = l.Name, Age = l.Age };

                foreach (var v in listAnonymousTypes)

                        // v - 匿名類型，可以在Visual Studio中得到編譯時檢查和完整的intellisense

                        string name = v.Name;

                        int age = v.Age;

                }

                // 聲明匿名類型：将new關鍵詞後面的類型名稱省略掉

                var person = new { Name = "webabcd", Age = 27 };

                // person - 匿名類型，可以在Visual Studio中得到編譯時檢查和完整的intellisense

                string myName = person.Name;

                int myAge = person.Age;

OK