举例讲解C#编程中委托的实例化使用

using System;// Define a custom delegate that has a string parameter and returns void.delegate void CustomDel(string s);class TestClass{  // Define two methods that have the same signature as CustomDel.  static void Hello(string s)  {    System.Console.WriteLine(" Hello, {0}!", s);  }  static void Goodbye(string s)  {    System.Console.WriteLine(" Goodbye, {0}!", s);  }  static void Main()  {    // Declare instances of the custom delegate.    CustomDel hiDel, byeDel, multiDel, multiMinusHiDel;    // In this example, you can omit the custom delegate if you     // want to and use Action<string> instead.    //Action<string> hiDel, byeDel, multiDel, multiMinusHiDel;    // Create the delegate object hiDel that references the    // method Hello.    hiDel = Hello;    // Create the delegate object byeDel that references the    // method Goodbye.    byeDel = Goodbye;    // The two delegates, hiDel and byeDel, are combined to     // form multiDel.     multiDel = hiDel + byeDel;    // Remove hiDel from the multicast delegate, leaving byeDel,    // which calls only the method Goodbye.    multiMinusHiDel = multiDel - hiDel;    Console.WriteLine("Invoking delegate hiDel:");    hiDel("A");    Console.WriteLine("Invoking delegate byeDel:");    byeDel("B");    Console.WriteLine("Invoking delegate multiDel:");    multiDel("C");    Console.WriteLine("Invoking delegate multiMinusHiDel:");    multiMinusHiDel("D");  }}

Invoking delegate hiDel: Hello, A!Invoking delegate byeDel: Goodbye, B!Invoking delegate multiDel: Hello, C! Goodbye, C!Invoking delegate multiMinusHiDel: Goodbye, D!

 // Declare a delegate.delegate void Del(string str);// Declare a method with the same signature as the delegate.static void Notify(string name){  Console.WriteLine("Notification received for: {0}", name);} // Create an instance of the delegate.Del del1 = new Del(Notify);

// C# 2.0 provides a simpler way to declare an instance of Del.Del del2 = Notify;

// Instantiate Del by using an anonymous method.Del del3 = delegate(string name)  { Console.WriteLine("Notification received for: {0}", name); };

// Instantiate Del by using a lambda expression.Del del4 = name => { Console.WriteLine("Notification received for: {0}", name); };

// 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);    }  }}

Paperback Book Titles:  The C Programming Language  The Unicode Standard 2.0  Dogbert's Clues for the CluelessAverage Paperback Book Price: $23.97

public delegate void ProcessBookDelegate(Book book);

bookDB.ProcessPaperbackBooks(PrintTitle);

bookDB.ProcessPaperbackBooks(totaller.AddBookToTotal);

processBook(b);