Swift 3，NotificationCenter观察员失踪发布通知

Question

There seems to be a few changes surrounding the NotificationCenter in Swift 3 and I can't seem to quite get it right.

Using:

Apple Swift version 3.0.2 (swiftlang-800.0.63 clang-800.0.42.1)

I have a singleton object:

class Notifications {

    private static let pipeline = Notifications()
    ...

That receives and enqueues items subscribing to NotificationsPipelineProtocol . (They are all pure swift, no Objective-C NSObjects here.)

    private func enqueueNotification(_ notification: NotificationsPipelineProtocol) {
        ...

in which it adds itself as an observer to the NotificationCenter

        NotificationCenter.default.addObserver(self,
                                       selector: #selector(Notifications.didReceiveNotificationCompletion(_:)),
                                       name: notification.completionNotificationName,
                                       object: notification)

NOTE - notification.completionNotificationName is a computed variable that produces a Notification.Name item.

But when the NotificationsPipelineProtocol item posts to the NotificationCenter:

NotificationCenter.default.post(name: self.completionNotificationName, object: self)

The observer does not call it's associated subscribed method:

    @objc private func didReceiveNotificationCompletion(_ notification : Notification) {
    ...

Might you know why? Is there a way to check to see in NotificationCenter to which notifications a particular item is subscribed to? Is perhaps the singleton object dropping it's observation? Maybe the #selector has been improperly formatted?

XCode gives me no warnings or errors.

Thanks in advance.

Answer 1

You are passing the NotificationPipelinesProtocol object to addObserver . This means that you will only receive notifications posted by that object . If you want to receive notifications of the specified name posted by any object then you should pass nil :

NotificationCenter.default.addObserver(self,
                                       selector: #selector(Notifications.didReceiveNotificationCompletion(_:)),
                                       name: notification.completionNotificationName,
                                       object: nil)