有用

 static void Main(string[] args)
        {
            string a="liu";
            string b="li";
            Swap<string>(ref a,ref b);
            Console.WriteLine("{0},{1}",a,b);
        }
        public static  void Swap<T>(ref T a, ref T b)
        {
            T c ;
            c = a;
            a = b;
            b = c;
        }