C#使用委托

using System;
using System.IO;

namespace DelegateAppl {

   class PrintString {
      static FileStream fs;
      static StreamWriter sw;

      // delegate declaration
      public delegate void printString(string s);

      // this method prints to the console
      public static void WriteToScreen(string str) {
         Console.WriteLine("The String is: {0}", str);
      }

      //this method prints to a file
      public static void WriteToFile(string s) {
         fs = new FileStream("c:/message.txt",
         FileMode.Append, FileAccess.Write);
         sw = new StreamWriter(fs);
         sw.WriteLine(s);
         sw.Flush();
         sw.Close();
         fs.Close();
      }

      // this method takes the delegate as parameter and uses it to
      // call the methods as required
      public static void sendString(printString ps) {
         ps("Hello World");
      }

      static void Main(string[] args) {
         printString ps1 = new printString(WriteToScreen);
         printString ps2 = new printString(WriteToFile);
         sendString(ps1);
         sendString(ps2);
         Console.ReadKey();
      }
   }
}