iOS isKindOfClass与isMemberOfClass的区别

先看一下官方文档的说法

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.
//调用者是给定类的实例或者是给定类的子类的实例

isMemberOfClass: Returns a Boolean value that indicates 
whether the receiver is an instance of a given class.
//调用者是不是给定类的实例
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而后看一道题目：

BOOL res1 = [(id)[NSObject class] isKindOfClass:[NSObject class]];
BOOL res2 = [(id)[NSObject class] isMemberOfClass:[NSObject class]];
BOOL res3 = [(id)[xxObj class] isKindOfClass:[xxObj class]];
BOOL res4 = [(id)[xxObj class] isMemberOfClass:[xxObj class]];

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答案是：YES / NO / NO / NO

协议有一套类方法的隐藏实现，因此编译运行正常； 因为NSObject meta class的父类为NSObject class，因此只有第一句为YES 看一下图就明白了：