瓶水相逢 - 艾小克

Keeping a low profile.

2008-05-17

C# 3.0 - Extension Methods 練習

C# 3.0 - Extension Methods 練習

C# 3.0 的新語言特性 Extension Methods，可以讓程式設計師對現有的類別增加額外的靜態方法。

以下 Extension Methods 範例，對系統 string 類別擴充 ToMD5() 方法與 ToSHA1() 方法，對 int 類別擴充 Square() 與 Cube() 方法。

首先，建立自訂命名 MyEctensionMethods 的命名空間，並建立自訂命名 StringExtensionMethods 靜態類別。最後，建立 public static string ToMD5(this string source) 的靜態方法，其中參數必須以 this string s 方式宣告：以 this 開頭，中間是符合擴充類別 stirng 的型態，最後是自訂變數名稱 source。

   1:  namespace MyExtensionMethods
   2:  {
   3:      /// <summary>
   4:      /// 字串型態的Extension Methods
   5:      /// </summary>
   6:      public static class StirngExtensionMethods
   7:      {
   8:          /// <summary>
   9:          /// 取得 MD5 加密字串
  10:          /// </summary>
  11:          public static string ToMD5(this string source)
  12:          {
  13:              MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
  14:              byte[] bytValue = Encoding.UTF8.GetBytes(source);
  15:              byte[] bytHash = md5.ComputeHash(bytValue);
  16:              md5.Clear();
  17:   
  18:              StringBuilder sb = new StringBuilder();
  19:              for (int i = 0; i < bytHash.Length; i++)
  20:              {
  21:                  sb.Append(bytHash[i].ToString("X").PadLeft(2, '0'));
  22:              }
  23:   
  24:              return sb.ToString().ToLower();
  25:          }
  26:      }
  27:  }

 

 

 

完整範例，包含系統 string 類別擴充 ToMD5() 方法與 ToSHA1() 方法，對 int 類別擴充 Square() 與 Cube() 方法。

   1:  namespace MyExtensionMethods
   2:  {
   3:      /// <summary>
   4:      /// 字串型態的 Extension Methods
   5:      /// </summary>
   6:      public static class StirngExtensionMethods
   7:      {
   8:          /// <summary>
   9:          /// 取得 MD5 加密字串
  10:          /// </summary>
  11:          public static string ToMD5(this string source)
  12:          {
  13:              MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
  14:              byte[] bytValue = Encoding.UTF8.GetBytes(source);
  15:              byte[] bytHash = md5.ComputeHash(bytValue);
  16:              md5.Clear();
  17:   
  18:              StringBuilder sb = new StringBuilder();
  19:              for (int i = 0; i < bytHash.Length; i++)
  20:              {
  21:                  sb.Append(bytHash[i].ToString("X").PadLeft(2, '0'));
  22:              }
  23:   
  24:              return sb.ToString().ToLower();
  25:          }
  26:   
  27:          /// <summary>
  28:          /// 取得 SHA-1 加密字串
  29:          /// </summary>
  30:          public static string ToSHA1(this string source)
  31:          {
  32:              SHA1CryptoServiceProvider sha1 = new SHA1CryptoServiceProvider();
  33:              byte[] bytValue = Encoding.UTF8.GetBytes(source);
  34:              byte[] bytHash = sha1.ComputeHash(bytValue);
  35:              sha1.Clear();
  36:   
  37:              StringBuilder sb = new StringBuilder();
  38:              for (int i = 0; i < bytHash.Length; i++)
  39:              {
  40:                  sb.Append(bytHash[i].ToString("X").PadLeft(2, '0'));
  41:              }
  42:   
  43:              return sb.ToString().ToLower();
  44:          }
  45:      }
  46:   
  47:      /// <summary>
  48:      /// 整數型態的 Extension Methods
  49:      /// </summary>
  50:      public static class IntExtensionMethods
  51:      {
  52:          /// <summary>
  53:          /// 取得平方值
  54:          /// </summary>
  55:          public static int Square(this int i)
  56:          {
  57:              return i * i;
  58:          }
  59:   
  60:          /// <summary>
  61:          /// 取得立方值
  62:          /// </summary>
  63:          public static int Cube(this int i)
  64:          {
  65:              return i * i * i;
  66:          }
  67:      }
  68:  }

 

 

 

使用方式：引入 MyEctensionMethods 的命名空間即可 using MyEctensionMethods;，對於相關擴充 string 與 int 類別，intellisense 就會自洞代初剛剛實作 string 類別的 ToMD5() 方法與 ToSHA1() 方法，對 int 類別擴充 Square() 與 Cube() 方法。

ExtensionMethods_001

ExtensionMethods_002 

   1:  string s = "測試";
   2:  string msg = string.Format("{0}, MD5: {1}, SHA1: {2}", s, s.ToMD5(), s.ToSHA1());
   3:  Console.Write(msg);
   4:   
   5:  Console.WriteLine();
   6:   
   7:  int i = 10;
   8:  string outString = string.Format("{0}, {0}^2: {1}, {0}^3: {2}", i, i.Square(), i.Cube());
   9:  Console.Write(outString);

 

 

 

輸出：

測試, MD5: b7dfcd49856b273e35b9504a921c8078, SHA1: 8b2da228cf9412ae0cc10113c08c779821bbc19d
10, 10^2: 100, 10^3: 1000