isKindOfClass: returns YES if the receiver is an instance of the specified class or an instance of any class that inherits from the specified class.
isMemberOfClass: returns YES if the receiver is an instance of the specified class.
但是这样尽量少使用吧， ruby说duck typing.比较少依赖类型。
isKindOfClass isMemeberOfClass 的区分
原文：http://www.cnblogs.com/studyNT/p/4499989.html