NSNotificationCenter事件是同步还是异步接收的? [英] Are NSNotificationCenter events received synchronously or asynchronously?
问题描述
如果一个类注册了某个类型的 NSNotificationCenter
事件,而另一个类发布了该类型的事件,那么接收器中的代码将在(同步)之前或之后执行(异步)发布课程继续?
If a class registers for NSNotificationCenter
events of a certain type and another class posts an event of that type, will the code in the receiver execute before (synchronously) or after (asynchronously) the posting class continues?
- (void)poster {
[[NSNotificationCenter defaultCenter]
postNotificationWithName:@"myevent"
object:nil];
NSLog(@"Hello from poster");
}
- (void)receiver {
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector:(mySelector)
name:@"myevent"
object:nil];
}
- (void) mySelector:(NSNotification *) notification {
NSLog(@"Hello from receiver");
}
在上面的代码示例中,来自接收器的Hello将在之前打印或者在来自调用者的Hello之后?
In the code example above, will "Hello from receiver" be printed before or after "Hello from caller"?
推荐答案
如NSNotificationCenter的文档中所述NSNotificationCenter类参考通知同步。
As stated in the documentation for NSNotificationCenter NSNotificationCenter Class Reference notifications are posted synchronously.
通知中心同步向观察者发送通知。
换句话说,postNotification:方法在所有观察者都收到并处理通知之前不会返回。要异步发送通知,请使用 NSNotificationQueue 。
A notification center delivers notifications to observers synchronously. In other words, the postNotification: methods do not return until all observers have received and processed the notification. To send notifications asynchronously use NSNotificationQueue.
在多线程应用程序中,通知始终在发布通知的线程中传递,这可能与观察者注册的线程不同。
In a multithreaded application, notifications are always delivered in the thread in which the notification was posted, which may not be the same thread in which an observer registered itself.
希望它可以帮到你。
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