委托实例讲解-优快云博客

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Delegate
{
   //把方法作为方法的参数,委托必须与传递的方法具有相同的参数类型和个数,通过委托动态指定要执行哪个方法
    public class Man
    {
        private string name;
        public Man(string name)
        {
            this.name = name;
        }
        public void eat(string food)
        {
            Console.WriteLine(name + "吃" + food);
        }
    }
    /// <summary>
    /// 定义委托
    /// </summary>
    /// <param name="food"></param>
    public delegate void EatDelegate(string food);
    public  class Program
    {
       //params 不定参数
        static void EatToghter(string food,params EatDelegate [] values)
        {
            if (values == null)
            {
                Console.WriteLine("结束!");
            }
            else
            {
                EatDelegate eatDelegate = null;
                foreach (EatDelegate ed in values)
                {
                    eatDelegate += ed;
                }
                eatDelegate(food);
            }

        }

        static void Main(string[] args)
        {
            Man zs = new Man("张三");
            Man ls = new Man("李思");
            Man ww = new Man("王五");
            EatDelegate _zs = new EatDelegate(zs.eat);
            EatDelegate _ls = new EatDelegate(ls.eat);
            EatDelegate _ww = new EatDelegate(ww.eat);
            EatDelegate eatlink = null;
            eatlink += _zs + _ls + _ww;//+=委托链
            eatlink("橘子");
            Console.WriteLine("------------");
            eatlink -= _zs;// _=去除委托
            eatlink("西瓜");
            Console.WriteLine("------------");
            EatToghter("苹果", _zs, _ls, _ww);
            Console.WriteLine("------------");
            EatToghter("香蕉", _ls, _ww);
            EatToghter(null, null);
        }
    }
}

下面的示例阐释声明、实例化和使用委托。BookDB 类封装一个书店数据库，它维护一个书籍数据库。

它公开 ProcessPaperbackBooks 方法，该方法在数据库中查找所有平装书，并对每本平装书调用一个委托。

所使用的 delegate 类型称为 ProcessBookDelegate。Test 类使用该类输出平装书的书名和平均价格。

委托的使用促进了书店数据库和客户代码之间功能的良好分隔。客户代码不知道书籍的存储方式和书店代码查找平装书的方式。

书店代码也不知道找到平装书后将对平装书进行什么处理。

Code
using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;

namespace Bookstore
{


    // 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:
    //声明一个新的委托类型。每个委托类型都描述参数的数目和类型，以及它可以封装的方法的返回值类型。
    //每当需要一组新的参数类型或新的返回值类型时，都必须声明一个新的委托类型。实例化委托。
    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)
                {
                    /*创建委托对象后，通常将委托对象传递给将调用该委托的其他代码。
                    通过委托对象的名称（后面跟着要传递给委托的参数，括在括号内）调用委托对象*/
                    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:
            /*明了委托类型后，必须创建委托对象并使之与特定方法关联。
            这是通过将 PrintTitle 方法传递给 ProcessPaperbackBooks 方法来完成的*/
            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);
        }
    }
}

转载于:https://www.cnblogs.com/hubcarl/archive/2009/05/16/1458488.html