// 声明一个委托    delegate void Printer(string s);    class TestClass    {        static void Main()        {            //lambda表达式            Printer pp = x => {                 Console.WriteLine("print:" + x);            };            pp("sky");            //匿名方法的语法：delegate(){//里边是代码块}            // 摘要:            //     Initializes a new instance of the System.Threading.Thread class.            //            // 参数:            //   start:            //     A System.Threading.ThreadStart delegate that represents the methods to be            //     invoked when this thread begins executing.            //            // 异常:            //   System.ArgumentNullException:            //     The start parameter is null.            System.Threading.Thread t1 = new System.Threading.Thread              (delegate()              {                  System.Console.Write("Hello, ");                  System.Console.WriteLine("World!");              });            t1.Start();            // 匿名函数            Printer p = delegate(string j)            {                System.Console.WriteLine(j);            };            // Results from the anonymous delegate call:            p("The delegate using the anonymous method is called.");            // 委托：将方法作为方法的参数            //下边将方法绑定到委托            //参考：张子阳的c#委托和事件http://www.cnblogs.com/JimmyZhang/archive/2007/09/23/903360.html            p = new Printer(TestClass.DoWork);            p += TestClass.DoWork1;            // p -= TestClass.DoWork;            //p -= TestClass.DoWork1;            // Results from the old style delegate call:            p("The delegate using the named method is called.");                  }        // The method associated with the named delegate:        static void DoWork(string k)        {            System.Console.WriteLine(k);        }        static void DoWork1(string k)        {            System.Console.WriteLine(k);        }    }

//无参数的委托

 // 声明一个委托    delegate void del();    class TestClass    {        static void Main()        {            del myDelegate1 = () =>            {                Console.WriteLine("00xx");            };            myDelegate1();            System.Threading.Thread t1 = new System.Threading.Thread             (()=>             {                 System.Console.Write("Hello, ");                 System.Console.WriteLine("World!");             });            t1.Start();             t1 = new System.Threading.Thread             (delegate()             {                 System.Console.Write("Hello, ");                 System.Console.WriteLine("World!");             });            t1.Start();        }    }

// A set of classes for handling a bookstore:namespace Bookstore{    using System.Collections;    // Describes a book in the book list:    public struct Book    {        public string Title;        // Title of the book.        public string Author;       // Author of the book.        public decimal Price;       // Price of the book.        public bool Paperback;      // Is it paperback?        public Book(string title, string author, decimal price, bool paperBack)        {            Title = title;            Author = author;            Price = price;            Paperback = paperBack;        }    }    // Declare a delegate type for processing a book:    public delegate void ProcessBookDelegate(Book book);    // Maintains a book database.    public class BookDB    {        // List of all books in the database:        ArrayList list = new ArrayList();        // Add a book to the database:        public void AddBook(string title, string author, decimal price, bool paperBack)        {            list.Add(new Book(title, author, price, paperBack));        }        // Call a passed-in delegate on each paperback book to process it:         public void ProcessPaperbackBooks(ProcessBookDelegate processBook)        {            foreach (Book b in list)            {                if (b.Paperback)                    // Calling the delegate:                    processBook(b);            }        }    }}// Using the Bookstore classes:namespace BookTestClient{    using Bookstore;    // Class to total and average prices of books:    class PriceTotaller    {        int countBooks = 0;        decimal priceBooks = 0.0m;        internal void AddBookToTotal(Book book)        {            countBooks += 1;            priceBooks += book.Price;        }        internal decimal AveragePrice()        {            return priceBooks / countBooks;        }    }    // Class to test the book database:    class TestBookDB    {        // Print the title of the book.        static void PrintTitle(Book b)        {            System.Console.WriteLine("   {0}", b.Title);        }        // Execution starts here.        static void Main()        {            BookDB bookDB = new BookDB();            // Initialize the database with some books:            AddBooks(bookDB);            // Print all the titles of paperbacks:            System.Console.WriteLine("Paperback Book Titles:");            // Create a new delegate object associated with the static             // method Test.PrintTitle:            bookDB.ProcessPaperbackBooks(PrintTitle);            // Get the average price of a paperback by using            // a PriceTotaller object:            PriceTotaller totaller = new PriceTotaller();            // Create a new delegate object associated with the nonstatic             // method AddBookToTotal on the object totaller:            bookDB.ProcessPaperbackBooks(totaller.AddBookToTotal);            System.Console.WriteLine("Average Paperback Book Price: ${0:#.##}",                    totaller.AveragePrice());        }        // Initialize the book database with some test books:        static void AddBooks(BookDB bookDB)        {            bookDB.AddBook("The C Programming Language", "Brian W. Kernighan and Dennis M. Ritchie", 19.95m, true);            bookDB.AddBook("The Unicode Standard 2.0", "The Unicode Consortium", 39.95m, true);            bookDB.AddBook("The MS-DOS Encyclopedia", "Ray Duncan", 129.95m, false);            bookDB.AddBook("Dogbert‘s Clues for the Clueless", "Scott Adams", 12.00m, true);        }    }}

在C#中使用线程的方法很多，使用委托的BeginInvoke和EndInvoke方法就是其中之一。BeginInvoke方法可以使用线程异步地执行委托所指向的方法。然后通过EndInvoke方法获得方法的返回值（EndInvoke方法的返回值就是被调用方法的返回值），或是确定方法已经被成功调用。我们可以通过四种方法从EndInvoke方法来获得返回值。

委托和接口都允许类设计器分离类型声明和实现。任何类或结构都能继承和实现给定的接口。可以为任何类上的方法创建委托，前提是该方法符合委托的方法签名。接口引用或委托可由不了解实现该接口或委托方法的类的对象使用。既然存在这些相似性，那么类设计器何时应使用委托，何时又该使用接口呢？在以下情况下，请使用委托：当使用事件设计模式时。当封装静态方法可取时。当调用方不需要访问实现该方法的对象中的其他属性、方法或接口时。需要方便的组合。当类可能需要该方法的多个实现时。在以下情况下，请使用接口：当存在一组可能被调用的相关方法时。当类只需要方法的单个实现时。当使用接口的类想要将该接口强制转换为其他接口或类类型时。当正在实现的方法链接到类的类型或标识时：例如比较方法。使用单一方法接口而不使用委托的一个很好的示例是 IComparable 或泛型版本 IComparable<(Of <(T>)>)。IComparable 声明 CompareTo 方法，该方法返回一个整数，指定相同类型的两个对象之间的小于、等于或大于关系。IComparable 可用作排序算法的基础。虽然将委托比较方法用作排序算法的基础是有效的，但是并不理想。因为进行比较的能力属于类，而比较算法不会在运行时改变，所以单一方法接口是理想的