深入C#筆記（一）---Action

Action的使用

  

Action<T> Delegate

概述：Encapsulates a method that has a single parameter and does not return a value.

描述：You can use the Action<T> delegate to pass a method as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have one parameter that is passed to it by value, and it must not return a value. (In C#, the method must return void. Typically, such a method is used to perform an operation.

個人理解：

• 用一種更簡潔的方式創建委託
• 作爲IEnumerable<T>某些方法的參數，例如Forecach，
• 創建Acton實例可以用傳統的委託方法，也可以用Lambda表達式，當然很多時候是我們可以不顯示創建一個Action，但實際上我們要知道，創建的是Action對象

一般用法：

using System;
using System.Windows.Forms;

public class TestAction1
{
   public static void Main()
   {
      Action<string> messageTarget; 

      if (Environment.GetCommandLineArgs().Length > 1)
         messageTarget = ShowWindowsMessage;
      else
         messageTarget = Console.WriteLine;

      messageTarget("Hello, World!");   
   }      

   private static void ShowWindowsMessage(string message)
   {
      MessageBox.Show(message);      
   }
}

使用委託以及Lambda的方式：

using System;
using System.Windows.Forms;

public class TestAnonMethod
{
   public static void Main()
   {
      Action<string> messageTarget; 


      //委託
      if (Environment.GetCommandLineArgs().Length > 1)
         messageTarget = delegate(string s) { ShowWindowsMessage(s); };
      else
         messageTarget = delegate(string s) { Console.WriteLine(s); };

  
       //Lambda
      if (Environment.GetCommandLineArgs().Length > 1)
         messageTarget = s => ShowWindowsMessage(s); 
      else
         messageTarget = s => Console.WriteLine(s);



      messageTarget("Hello, World!");
   }

   private static void ShowWindowsMessage(string message)
   {
      MessageBox.Show(message);      
   }
}