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

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）

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; 

     本文轉自webabcd 51CTO部落格，原文連結：http://blog.51cto.com/webabcd/344994，如需轉載請自行聯系原作者