第一個參數(shù)告訴方法需要何種格式的輸出，而第二個IFormatProvider的參數(shù)則允許類型的使用者自定義格式化方法，在本文實現(xiàn)的ToString()方法中，并沒有使用到第二個參數(shù)。關于IFormatProvider接口請閱讀文章《ICustomFormatter及IFormatProvider接口用法揭秘》，本文不做過多說明。下面是完整的實例代碼。

using System;
using System.Globalization;


namespace GreetingExample
{
  public class Greeting : IFormattable
  {
    private string name;
    public Greeting(string name)
    {
      this.name = name;
    }


    public override string ToString()
    {
      return this.ToString("CN",CultureInfo.CurrentCulture);
    }


    public string ToString(string format)
    {
      return this.ToString(format,CultureInfo.CurrentCulture);
    }


    public string ToString(string format, IFormatProvider provider)
    {
      if (String.IsNullOrEmpty(format)) format = "CN";
      if (provider == null) provider = CultureInfo.CurrentCulture;
      switch (format.ToUpper())
      {
        case "CN":
        case "TW":
          return "你好，" + name.ToString();
        case "US":
        case "GB":
          return "Hello，" + name.ToString();
        case "JP":
          return "こんにちは，" + name.ToString();
        default:
          throw new FormatException(String.Format("The {0} format string is not supported.", format));
      }
    }
  }
}
using System;


namespace GreetingExample
{
  class Program
  {
    static void Main(string[] args)
    {
      Greeting greeting = new Greeting("三五月兒");
      Console.WriteLine(greeting.ToString("CN"));
      Console.WriteLine(greeting.ToString("US"));
      Console.WriteLine(greeting.ToString("JP"));
    }
  }
}

下面是代碼的運行結(jié)果。