iOS之iskindofclass 与objc_opt_isKindOfClass

闲暇时看到一个问题。关于 isKindOfClass isMemberOfClass 一个看似很简单的问题。若要探索，源码一看就知道答案。源码objc的源码中

测试一下。

    BOOL kre1 = [[NSObject class] isKindOfClass:[NSObject class]];
    BOOL kre2 = [[NSObject class] isMemberOfClass:[NSObject class]];
    BOOL kre3 = [[GoodGame class] isKindOfClass:[GoodGame class]];
    BOOL kre4 = [[GoodGame class] isMemberOfClass:[GoodGame class]];
    BOOL kre5 = [[NSObject alloc] isKindOfClass:[NSObject class]];
    BOOL kre6 = [[NSObject alloc] isMemberOfClass:[NSObject class]];
    BOOL kre7 = [[GoodGame alloc] isKindOfClass:[GoodGame class]];
    BOOL kre8 = [[GoodGame alloc] isMemberOfClass:[GoodGame class]];
    NSLog(@"\n k1 :%hhd\n k2 :%hhd\n k3 :%hhd\n k4 :%hhd\n k5:%hhd\n k6:%hhd\n k7:%hhd\n k8:%hhd\n ",kre1,kre2,kre3,kre4,kre5, kre6, kre7, kre8);}

答案很简单

提个疑问为什么

在看源码的过程中联想 alloc 方法，并没有在底层调用alloc 。通过符号断点来查看。

真的神头鬼脸，没调用isKindOfClass 而是 objc_opt_isKindOfClass。 源码搜索一下objc_opt_isKindOfClass

objc_opt_isKindOfClass

BOOL

objc_opt_isKindOfClass(id obj, Class otherClass)

{

#if __OBJC2__
    if (slowpath(!obj)) return NO;
///  isa  实例对象的isa  -> 类对象 -> 元类对象 -> 根元类（NSObject） -> 自身（NSObject）
///  Superclass 子类  -> 父类对象 -> NSObject  -> nil
///  函数流程 obj->isa-> 如果 相等结束   否则 Superclass 继续
    Class cls = obj->getIsa();
    if (fastpath(!cls->hasCustomCore())) {
        for (Class tcls = cls; tcls; tcls = tcls->getSuperclass()) {
            if (tcls == otherClass) return YES;
        }
        return NO;
    }
#endif
    return ((BOOL(*)(id, SEL, Class))objc_msgSend)(obj, @selector(isKindOfClass:), otherClass);

}

isKindOfClass

/// 类方法
+ (BOOL)isKindOfClass:(Class)cls {
/// 函数 obj(class) -> isa -> Superclass
    for (Class tcls = self->ISA(); tcls; tcls = tcls->getSuperclass()) {
        if (tcls == cls) return YES;
    }
    return NO;
}

/// 对象方法
- (BOOL)isKindOfClass:(Class)cls {
/// 函数 obj(class) -> isa -> Superclass
    for (Class tcls = [self class]; tcls; tcls = tcls->getSuperclass()) {
        if (tcls == cls) return YES;
    }
    return NO;
}

objc_opt_isKindOfClass isKindOfClass看上去没啥区别。实际上上进行了消息的转发。 看下题目的结果

    /// NSObject isa  rootNSObject superclas NSObject  is   NSObject =》 1
    BOOL kre1 = [[NSObject class] isKindOfClass:[NSObject class]];
    
    /// NSObject isa  rootNSObject  is   NSObject =》 0
    BOOL kre2 = [[NSObject class] isMemberOfClass:[NSObject class]];
    
    /// GoodGame isa  NSObject superclas nil is   GoodGame =》 0
    BOOL kre3 = [[GoodGame class] isKindOfClass:[GoodGame class]];
    
     /// GoodGame isa  NSObject  is   GoodGame =》 0
    BOOL kre4 = [[GoodGame class] isMemberOfClass:[GoodGame class]];
    
     /// obj(NSObject) isa  NSObject  is   NSObject =》 1
    BOOL kre5 = [[NSObject alloc] isKindOfClass:[NSObject class]];
    
    /// obj(NSObject) isa  NSObject  is   NSObject =》 1
    BOOL kre6 = [[NSObject alloc] isMemberOfClass:[NSObject class]];
   
    /// obj(GoodGame) isa  GoodGame  is   GoodGame =》 1
    BOOL kre7 = [[GoodGame alloc] isKindOfClass:[GoodGame class]];
    
    /// obj(GoodGame) isa  GoodGame  is   GoodGame =》 1
    BOOL kre8 = [[GoodGame alloc] isMemberOfClass:[GoodGame class]];
    NSLog(@"\n k1 :%hhd\n k2 :%hhd\n k3 :%hhd\n k4 :%hhd\n k5:%hhd\n k6:%hhd\n k7:%hhd\n k8:%hhd\n ",kre1,kre2,kre3,kre4,kre5, kre6, kre7, kre8);}

到此虽然。区别在于 在__OBJC2__时有所区别。

• 获取isa的区别 getIsa()

objc_object::getIsa() 

{
    if (fastpath(!isTaggedPointer())) return ISA();
\
    extern objc_class OBJC_CLASS_$___NSUnrecognizedTaggedPointer;

    uintptr_t slot, ptr = (uintptr_t)this;

    Class cls;
    slot = (ptr >> _OBJC_TAG_SLOT_SHIFT) & _OBJC_TAG_SLOT_MASK;

    cls = objc_tag_classes[slot];

    if (slowpath(cls == (Class)&OBJC_CLASS_$___NSUnrecognizedTaggedPointer)) {

        slot = (ptr >> _OBJC_TAG_EXT_SLOT_SHIFT) & _OBJC_TAG_EXT_SLOT_MASK;

        cls = objc_tag_ext_classes[slot];

    }
    return cls;

}

ISA()

objc_object::ISA(bool authenticated)

{

    ASSERT(!isTaggedPointer());

    return isa.getDecodedClass(authenticated);

}

isTaggedPointer  
是 - 对象的值就是指针 
否 - 对象的值是指针指向的内存区域中的值

getIsa 然后调用 ISA() 神头鬼脸，既然一样，为什么搞如此复杂，原来以为发现了新大陆。带着满满的成就感琢磨了半天。研究半天网上一搜，尴了尬。