NSObject.h解（一）

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根据runtime中的objc4-646版本解析。

NSObject协议方法
第一个方法：判断是否和另一个对象相等

- (BOOL)isEqual:(id)obj {    return obj == self;}

第二个方法：获得自己

- (id)self {    return self;}

第三个方法：获得类对象

- (Class)class {    return object_getClass(self);}

第四个方法：执行选择子

- (id)performSelector:(SEL)sel {    if (!sel) [self doesNotRecognizeSelector:sel];    return ((id(*)(id, SEL))objc_msgSend)(self, sel);}- (id)performSelector:(SEL)sel withObject:(id)obj {    if (!sel) [self doesNotRecognizeSelector:sel];    return ((id(*)(id, SEL, id))objc_msgSend)(self, sel, obj);}- (id)performSelector:(SEL)sel withObject:(id)obj1 withObject:(id)obj2 {    if (!sel) [self doesNotRecognizeSelector:sel];    return ((id(*)(id, SEL, id, id))objc_msgSend)(self, sel, obj1, obj2);}

第四个方法：判断是否是某个类，就是不停的循环，先从当前类开始找，如果不是，再从父类找，找到返回YES，否则返回NO

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

第五个方法：判断是否指着同一个类

- (BOOL)isMemberOfClass:(Class)cls {    return [self class] == cls;}

第六个方法：判断是否遵守某个协议，原理和第四个方法类似

- (BOOL)conformsToProtocol:(Protocol *)protocol {    if (!protocol) return NO;    for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {        if (class_conformsToProtocol(tcls, protocol)) return YES;    }    return NO;}

第七个方法：判断是否响应某个选择子

- (BOOL)respondsToSelector:(SEL)sel {    if (!sel) return NO;    return class_respondsToSelector_inst([self class], sel, self);}

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