舉例講授C#編程中拜托的實例化應用。本站提示廣大學習愛好者：（舉例講授C#編程中拜托的實例化應用）文章只能為提供參考，不一定能成為您想要的結果。以下是舉例講授C#編程中拜托的實例化應用正文
歸並拜托
本示例演示若何創立多播拜托。 拜托對象的一個有效屬性是：可使用 + 運算符將多個對象分派給一個拜托實例。多播拜托包括已分派拜托的列表。在挪用多播拜托時，它會按次序挪用列表中的拜托。只能歸並雷同類型的拜托。
- 運算符可用於從多播拜托中移除組件拜托。
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");
}
}
輸入：
Invoking delegate hiDel: Hello, A! Invoking delegate byeDel: Goodbye, B! Invoking delegate multiDel: Hello, C! Goodbye, C! Invoking delegate multiMinusHiDel: Goodbye, D!
聲明、實例化和應用拜托
在 C# 1.0 及更高版本中，可以按以下示例所示聲明拜托。
// 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 供給了更簡略的辦法來編寫下面的聲明，如以下示例所示。
// C# 2.0 provides a simpler way to declare an instance of Del. Del del2 = Notify;
在 C# 2.0 及更高版本中，還可使用匿名辦法來聲明和初始化拜托，如以下示例所示。
// Instantiate Del by using an anonymous method.
Del del3 = delegate(string name)
{ Console.WriteLine("Notification received for: {0}", name); };
在 C# 3.0 及更高版本中，還可使用 Lambda 表達式來聲明和實例化拜托，如以下示例所示。
// Instantiate Del by using a lambda expression.
Del del4 = name => { Console.WriteLine("Notification received for: {0}", name); };
上面的示例闡釋聲明、實例化和應用拜托。 BookDB 類封裝一個書店數據庫，它保護一個書本數據庫。它地下 ProcessPaperbackBooks 辦法，該辦法在數據庫中查找一切平裝書，並對每本平裝書挪用一個拜托。應用的 delegate 類型名為 ProcessBookDelegate。 Test 類應用該類打印平裝書的書名戰爭均價錢。
拜托的應用增進了書店數據庫和客戶代碼之間功效的優越分隔。客戶代碼不曉得書本的存儲方法和書店代碼查找平裝書的方法。書店代碼也不曉得找到平裝書後將對平裝書履行甚麼處置。
// 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);
}
}
}
輸入：
Paperback Book Titles: The C Programming Language The Unicode Standard 2.0 Dogbert's Clues for the Clueless Average Paperback Book Price: $23.97
靠得住編程
聲明拜托。
上面的語句聲明一個新的拜托類型。
public delegate void ProcessBookDelegate(Book book);
每一個拜托類型都描寫參數的數量和類型，和它可以封裝的辦法的前往值類型。每當須要一組新的參數類型或新的前往值類型時，都必需聲明一個新的拜托類型。
實例化拜托。
聲清楚明了拜托類型後，必需創立拜托對象並使之與特定辦法聯系關系。在上一個示例中，您經由過程按上面示例中的方法將 PrintTitle 辦法傳遞到 ProcessPaperbackBooks 辦法來完成這一點：
bookDB.ProcessPaperbackBooks(PrintTitle);
這將創立與靜態辦法 Test.PrintTitle 聯系關系的新拜托對象。相似地，對象 totaller 的非靜態辦法 AddBookToTotal 是按上面示例中的方法傳遞的：
bookDB.ProcessPaperbackBooks(totaller.AddBookToTotal);
在兩個示例中，都向 ProcessPaperbackBooks 辦法傳遞了一個新的拜托對象。
拜托創立後，它的聯系關系辦法就不克不及更改；拜托對象是弗成變的。
挪用拜托。
創立拜托對象後，平日將拜托對象傳遞給將挪用該拜托的其他代碼。經由過程拜托對象的稱號（前面隨著要傳遞給拜托的參數，括在括號內）挪用拜托對象。上面是拜托挪用的示例：
processBook(b);
與本例一樣，可以經由過程應用 BeginInvoke 和 EndInvoke 辦法同步或異步驟用拜托。
