动态识别类型

-(BOOL) isKindOfClass: classObj

is object a descendent or member of classObj
此对象是否是 classObj 的子孙或一员

-(BOOL) isMemberOfClass: classObj

is object a member of classObj
此对象是否是 classObj 的一员

-(BOOL) respondsToSelector: selector

does the object have a method named specifiec

by the selector
此对象是否有叫做selector 的 method

+(BOOL) instancesRespondToSelector: selector

does an object created by this class have the

ability to respond to the specified selector
此对象是否是由有能力响应指定 selector 的对象所产生

-(id) performSelector: selector

invoke the specified selector on the object
唤起此对象的指定selector