目录
class函数
先看下源码实现
- (Class)class {
return object_getClass(self);
}
+ (Class)class {
return self;
}
对象方法调用时通过object_getClass函数返回的是类对象。
类方法调用时直接返回self，即将自身返回也就是类对象。
所以不管对象方法class还是类方法class返回的都是类对象。
NSObject * obj = [[NSObject alloc] init];
//不管调用多少次class返回的都是类对象
[[[obj class] class] class];
[obj class];//返回类对象，之后调用class都返回自身
superclass函数
先看下源码实现
- (Class)superclass {
return [self class]->superclass;
}
+ (Class)superclass {
return self->superclass;
}
与class方法类似，对象方法superclass和类方法superclass返回的结果一样，都是父类的类对象。
不同的是一直调用superclass会一直向上找父类的父类
//Student:Person:NSObject
Student * stu = [[Student alloc] init];
[[stu superclass] superclass]//NSObject
isMemberOfClass
先看下源码实现
- (BOOL)isMemberOfClass:(Class)cls {
return [self class] == cls;
}
+ (BOOL)isMemberOfClass:(Class)cls {
return object_getClass((id)self) == cls;
}
对象方法：是拿类对象与cls对比是否相等。 类方法：是拿元类对象与cls对比是否相等。
先看下对象方法的示例
//Person:NSObject
Person * person = [[Person alloc] init];
//cls:Person
//[self class]:Person
//Person == Person所以打印结果为1
NSLog(@"%d",[person isMemberOfClass:[Person class]]);//1
//cls:NSObject
//[self class]:Person
//Person !=NSObject 所以打印结果为0
NSLog(@"%d",[person isMemberOfClass:[NSObject class]]);//0
再看下类方法的示例
//cls:Person
//object_getClass((id)self):Meta-Person
//Meta-Person != Person 所以打印结果为0
NSLog(@"%d",[Person isMemberOfClass:[Person class]]);//0
//cls:NSObject
//object_getClass((id)self):Meta-Person
//Meta-Person != NSObject 所以打印结果为0
NSLog(@"%d",[Person isMemberOfClass:[NSObject class]]);//0
//cls:Meta-Person
//object_getClass((id)self):Meta-Person
//Meta-Person == Meta-Person 所以打印结果为1
NSLog(@"%d",[Person isMemberOfClass:object_getClass([Person class])]);//1
isKindOfClass
先看下源码实现
- (BOOL)isKindOfClass:(Class)cls {
for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
+ (BOOL)isKindOfClass:(Class)cls {
for (Class tcls = object_getClass((id)self); tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
对象方法、类方法中都有一个for循环，一次比对不成功会继续与superclass比对，直到比对成功返回YES或者superclass为空时退出循环返回NO。
//Person:NSObject
Person * person = [[Person alloc] init];
//tcls:object_getClass((id)self):Person
//cls:Person
//Person == Person 打印结果为1
NSLog(@"%d",[person isKindOfClass:[Person class]]);//1
//tcls:object_getClass((id)self):Person
//cls:NSObject
//Person == NSObject 在循环内部Person->superclass NSObject
//NSObjcet == NSObject 打印结果为1
NSLog(@"%d",[person isKindOfClass:[NSObject class]]);//1
//tcls:object_getClass((id)self):Meta-Person
//cls:Person
//Meta-Person != Person 在循环内部Meta-Person->superclass Meta-NSObject
//Meta-NSObject != Person 在循环内部Meta-NSObject->superclass NSObject
//NSObject != Person 在循环内部 NSObject->superclass 为 nil 循环结束。
//打印结果为0
NSLog(@"%d",[Person isKindOfClass:[Person class]]);//0
//tcls:object_getClass((id)self):Meta-Person
//cls:NSObject
//Meta-Person != NSObject 在循环内部Meta-Person->superclass Meta-NSObject
//Meta-NSObject != NSObject 在循环内部Meta-NSObject->superclass NSObject
//NSObject == NSObject 在循环内部 返回YES 循环结束。
//打印结果为1
NSLog(@"%d",[Person isKindOfClass:[NSObject class]]);//1
分析下下面代码的打印结果
//0
NSLog(@"%d",[NSObject isMemberOfClass:[NSObject class]]);
//1
NSLog(@"%d",[NSObject isKindOfClass:[NSObject class]]);
//0
NSLog(@"%d",[Person isMemberOfClass:[Person class]]);
//0
NSLog(@"%d",[Person isKindOfClass:[Person class]]);
行者常至，为者常成！