isKindOfClass:
Returns a Boolean value that indicates whether the receiver is an instance of given class or an instance of any class that inherits from that class. (required)
isKindOfClass能确定一个对象是否是一个类的成员，或者是派生自该类的成员
isMemberOfClass:
Returns a Boolean value that indicates whether the receiver is an instance of a given class. (required)
isMemberOfClass只能确定一个对象是否是一个类的成员
例如：
[[NSMutableData data] isKindOfClass:[NSData class]]; // YES
[[NSMutableData data] isMemberOfClass:[NSData class]]; // NO