iOS isKindOfClass&isMemberOfClass解析

• 先回顾一下isa的走位图

  
  
  isa流程图.png

分析 re1-re4的代码

 BOOL re1 = [(id)[NSObject class] isKindOfClass:[NSObject class]];       //1
 BOOL re2 = [(id)[NSObject class] isMemberOfClass:[NSObject class]];     //0
 BOOL re3 = [(id)[XpPerson class] isKindOfClass:[LGPerson class]];       //0
 BOOL re4 = [(id)[XpPerson class] isMemberOfClass:[XpPerson class]];     //0

可以看得出isKindOfClass和isMemberOfClass的底层实现是

+ (BOOL)isKindOfClass:(Class)cls {
    for (Class tcls = self->ISA(); tcls; tcls = tcls->superclass) {
        if (tcls == cls) return YES;
    }
    return NO;
}
+ (BOOL)isMemberOfClass:(Class)cls {
    return self->ISA() == cls;
}

• re1 传进去的cls 是NSObject，Class tcls = self->ISA(),意思是tcls 等于self只向的isa类，根据对象isa走向图，可以知道NSObject指向的是元类(NSObject)->跟元类(NSObject),所以tcls = NSObject
  tcls = tcls->superclass,NSObject的superclass还是NSObject，所以cls=tcls 返回1
• re3 传进去cls是XpPerson，上面说了tcls = NSObject,现在cls=XpPerson,所以不等 返回0
• re2 类的元类 ==类?元类(元类NSObject) ==类(NSObject) ?显然不等 返回0
• re4 类的元类 ==类?元类(元类NSObject) ==类(XpPerson) ?显然不等 返回0

再分析 re5-re8的代码

BOOL re5 = [(id)[NSObject alloc] isKindOfClass:[NSObject class]];       //1
BOOL re6 = [(id)[NSObject alloc] isMemberOfClass:[NSObject class]];     //1
BOOL re7 = [(id)[XpPerson alloc] isKindOfClass:[XpPerson class]];       //1
BOOL re8 = [(id)[XpPerson alloc] isMemberOfClass:[XpPerson class]]; 

上面isKindOfClass和isMemberOfClass底层代码是

- (BOOL)isKindOfClass:(Class)cls {
    for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
        if (tcls == cls) return YES;
    }
    return NO;
}
- (BOOL)isMemberOfClass:(Class)cls {
    return [self class] == cls;
}

• re5 传进去的cls 是NSObject，Class tcls = [self class];意思是tcls 等于self的类，tcls = NSObject
  tcls = tcls->superclass,NSObject的superclass还是自己，所以cls=tcls 返回1
• re7 传进去cls是XpPerson，上面说了tcls = XpPerson,现在cls=XpPerson,所以不等 返回1
• re2[self class] =NSObject ,cls = NSObject 返回1
• re4 [self class] =XpPerson ,cls = XpPerson 返回1