c# 判断类是否实现了某个接口的三种方法

   B b = new B();
   if (b.GetType().GetInterface("ISay") != null)
             {
                 //如果实现了接口“ISay”,...
             }

 B b = new B();
  if (b is ISay)
             {
                 Console.WriteLine("类B实现了接口ISay");
             }

    B b = new B();
   ISay say = b as ISay;
             if (say != null)
             {
                 Console.WriteLine("类B实现了接口ISay");
             }