Delegate在C#中，是幹麼用的？

// A simple delegate example. 

   

using System;

   

// Declare a delegate. 

delegate string strMod(string str);

   

class DelegateTest {

  // Replaces spaces with hyphens.

  static string replaceSpaces(string a) {

    Console.WriteLine("Replaces spaces with hyphens.");

    return a.Replace(' ', '-');

  } 

   

  // Remove spaces.

  static string removeSpaces(string a) {

    string temp = "";

    int i;

   

    Console.WriteLine("Removing spaces.");

    for(i=0; i < a.Length; i++)

      if(a[i] != ' ') temp += a[i];

   

    return temp;

  } 

   

  // Reverse a string.

  static string reverse(string a) {

    string temp = "";

    int i, j;

   

    Console.WriteLine("Reversing string.");

    for(j=0, i=a.Length-1; i >= 0; i--, j++)

      temp += a[i];

   

    return temp;

  }

    

  public static void Main() { 

    // Construct a delegate.

    strMod strOp = new strMod(replaceSpaces);

    string str;

/* 

注意這邊，replaceSpaces這個function被當成strMod的參數傳進來，

這樣就完成委派，之後對strOp傳參數進去，就等同於對replaceSpaces傳參數

*/

   

    // Call methods through the delegate.

    str = strOp("This is a test.");

/*

所以當strOp在這邊傳入This is a test.的時候，相當於replaceSpaces("This is a test.")

會輸出　Resulting string: This-is-a-test.

*/

    Console.WriteLine("Resulting string: " + str);

    Console.WriteLine();

     

    strOp = new strMod(removeSpaces);

/* 現在又改註冊removeSpaces這個function */

    str = strOp("This is a test.");

    Console.WriteLine("Resulting string: " + str);

/* 會輸出　Resulting string: Thisisatest. */

    Console.WriteLine();

   

    strOp = new strMod(reverse);

    str = strOp("This is a test.");

    Console.WriteLine("Resulting string: " + str);

  }

}

The output from the program is shown here:

Replaces spaces with hyphens.

Resulting string: This-is-a-test.

   

Removing spaces.

Resulting string: Thisisatest.

   

Reversing string.

Resulting string: .tset a si sihT

參考書目

C#: The Complete Reference

by Herbert Schildt 

McGraw-Hill/Osborne © 2002 (933 pages) Citation

ISBN:9780072134858

Learn all aspects of the C# programming language that support the .NET Framework with this all-inclusive guide.

chapter 15 : Delegates and Events