C#.Net 类的同名方法重载调用顺序

C# Code:


public class MultiMethods
{
   /// <summary>
   /// 由可空值类型转换为日期
   /// </summary>
   /// <param name="p">可空值类型</param>
   /// <returns></returns>
   public static DateTime Convert(DateTime? p)
   {
      if (p == null) return DateTime.MinValue;
      return MultiMethods.Convert(p.ToString());
   }
   
   /// <summary>
   /// 由对象转换为日期
   /// </summary>
   /// <param name="p">对象</param>
   /// <returns></returns>
   public static DateTime Convert(Object p)
   {
      if (p == null) return DateTime.MinValue;
      return MultiMethods.Convert(p.ToString());
   }
   
   /// <summary>
   /// 由字符串转换为日期
   /// </summary>
   /// <param name="p">字符串</param>
   /// <returns></returns>
   public static DateTime Convert(string p)
   {
      if (p == null) return DateTime.MinValue;
      DateTime result;
      if (DateTime.TryParse(p.ToString(), out result))
      return result;
      else
      return DateTime.MinValue;
   }
   
}

//来源:C/S框架网(www.csframework.com) QQ:1980854898

C# Code:

DateTime D;

D = MultiMethods.Convert("2011-01-01");//结果：调用字符串string参数的方法
D = MultiMethods.Convert((Object)"2011-01-01");//结果：调用对象Object参数的方法
D = MultiMethods.Convert(DBNull.Value);//结果：调用对象Object参数的方法

DateTime? date = DateTime.Parse("2011-01-01");//可空值类型
date = null;//可空值类型
D = MultiMethods.Convert(date);//结果：调用可空值DateTime?类型参数的方法
 

//Error 1:The call is ambiguous between the following methods or properties:
//'CSFramework.MultiMethods.Convert(System.DateTime?)' and 'CSFramework.MultiMethods.Convert(string)'
//D:\My SourceCode\CSharp\Tech2010 Full Code\CSFramework\CSFramework\Program.cs 23 17 CSFramework

//D = MultiMethods.Convert(null); //编译不通过

null为空类型，提示Convert(System.DateTime?)和Convert(string)两个方法的参数不明确，产生二义性。