Swift NotificationCenter传递userInfo至视图控制器时崩溃求助

Hey there! Sorry to hear you're stuck with this crash when posting a notification—let’s break down the most common reasons this happens and how to fix them.

1. Your userInfo contains non-serializable objects #

NotificationCenter requires all objects in userInfo to be serializable (i.e., conform to NSCoding or be a Foundation framework type like NSString, NSNumber, NSArray, or NSDictionary). If you’re passing a custom object that doesn’t implement NSCoding, this will almost certainly cause a crash when posting the notification.

Fix: #

Either:

• Implement NSCoding for your custom object:

  class CustomUser: NSObject, NSCoding {
      let id: String
      let username: String
  
      init(id: String, username: String) {
          self.id = id
          self.username = username
      }
  
      // MARK: - NSCoding
      func encode(with coder: NSCoder) {
          coder.encode(id, forKey: "id")
          coder.encode(username, forKey: "username")
      }
  
      required init?(coder: NSCoder) {
          id = coder.decodeObject(forKey: "id") as? String ?? ""
          username = coder.decodeObject(forKey: "username") as? String ?? ""
      }
  }
  

• Or, convert your custom object into a dictionary of basic types before adding it to userInfo:

  let userDict = ["id": user.id, "username": user.username]
  NotificationCenter.default.post(name: .userUpdated, object: nil, userInfo: userDict)
  

2. The listener view controller has been deallocated (dangling pointer) #

If your view controller was dismissed/deallocated but you didn’t remove it as a notification observer, NotificationCenter will try to send the notification to a released object—this causes a classic "bad access" crash.

Fix: #

• Use weak self in your observer closure to avoid retaining the view controller unnecessarily:

  // When adding the observer
  NotificationCenter.default.addObserver(forName: .userUpdated, object: nil, queue: .main) { [weak self] notification in
      guard let self = self else { return } // Exit if the VC is gone
      self.handleUserUpdate(notification)
  }
  

• Always remove observers in your view controller’s deinit (even though block-based observers auto-remove, it’s a safe habit):

  deinit {
      NotificationCenter.default.removeObserver(self)
  }
  

3. You’re force-unwrapping userInfo in the receiver #

If you post the notification with userInfo: nil but your receiver uses let info = notification.userInfo! (force unwrap), this will crash immediately.

Fix: #

Use optional binding to safely access userInfo:

@objc func handleUserUpdate(_ notification: Notification) {
    guard let userInfo = notification.userInfo else {
        print("No user info received")
        return
    }
    // Extract values from userInfo safely
    guard let userId = userInfo["userId"] as? String else { return }
    // Do something with userId
}

4. Mismatched notification names (less likely to crash, but worth checking) #

While this won’t cause a crash directly, if your observer is listening for a different notification name than you’re posting, your receiver won’t trigger—and if your logic relies on that notification, it could lead to unexpected behavior (or indirect crashes).

Fix: #

Define notification names in a shared extension to avoid typos:

extension Notification.Name {
    static let userUpdated = Notification.Name("UserUpdatedNotification")
}

// Post with:
NotificationCenter.default.post(name: .userUpdated, object: nil, userInfo: userInfo)

// Listen with:
NotificationCenter.default.addObserver(forName: .userUpdated, ...)

Start by checking these areas—chances are one of them is causing your crash. Let me know if you need to dive deeper with specific code snippets!

内容的提问来源于stack exchange，提问作者rharding