objective-c - NSNotification 在父类(super class)中观察并在父类(super class)和子类中处理

Question

我有类 ParentClass 观察 NSNotification。 ParentClass 处理通知。 ChildClass 继承了 ParentClass，也负责处理通知。 发送通知的顺序是确定的吗？

换句话说，ParentClass 是否总是在 ChildClass 之前处理通知，反之亦然？

Answer 1

这取决于实例化哪些类以及如何实例化，形成实际对象。还要看子类是否调用super进行处理。否则，正如 NSNotificationCenter 的文档所说，接收通知的对象的顺序是随机的，并且不取决于您是子类还是父类(super class)。请考虑以下示例以便更好地理解:(由于您的解释不完全清楚，因此需要几个示例):

示例 1:两个不同的对象

ParentClass *obj1 = [[ParentClass alloc] init];
ChildClass *obj2 = [[ChildClass alloc] init];
// register both of them as listeners for NSNotificationCenter
// ...
// and now their order of receiving the notifications is non-deterministic, as they're two different instances

例子2:子类调用super

@implementation ParentClass

- (void) handleNotification:(NSNotification *)not
{
    // handle notification
}

@end

@ipmlementation ChildClass

- (void) handleNotification:(NSNotification *)not
{
    // call super
    [super handleNotification:not];
    // actually handle notification
    // now the parent class' method will be called FIRST, as there's one actual instace, and ChildClass first passes the method onto ParentClass
}

@end