NS超级观察超级和在超级和子级处理

Question

我有类ParentClass观察NSNotification。 ParentClass处理通知。 ChildClass继承ParentClass并处理通知。 通知传递的顺序是确定性的吗？

换句话说，ParentClass会在ChildClass之前处理通知，反之亦然？

Answer 1

它取决于哪些类被实例化以及如何形成实际的对象。这也取决于子类是否调用super来处理。否则，正如NSNotificationCenter的文档所说，接收通知的对象的顺序是随机的，并且不取决于您是否是子类或超类。考虑更好地理解下面的示例：（需要几个例子作为你的解释并不完全清楚）：

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