How to pass data using NotificationCenter in swift 3.0 and NSNotificationCenter in swift 2.0?

Question

I'm implementing socket.io in my swift ios app.

Currently on several panels I'm listening to the server and wait for incoming messages. I'm doing so by calling the getChatMessage function in each panel:

func getChatMessage(){
    SocketIOManager.sharedInstance.getChatMessage { (messageInfo) -> Void in
        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            //do sth depending on which panel user is
        })
    }
}

However I noticed it's a wrong approach and I need to change it - now I want to start listening for incoming messages only once and when any message comes - pass this message to any panel that listens to it.

So I want to pass the incoming message through the NSNotificationCenter. So far I was able to pass the information that something happened, but not pass the data itself. I was doing that by:

NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.showSpinningWheel(_:)), name: showSpinner, object: nil)

then I had a function called:

func showSpinningWheel(notification: NSNotification) {
}

and any time I wanted to call it I was doing:

NSNotificationCenter.defaultCenter().postNotificationName(hideSpinner, object: self)

So how can I pass the object messageInfo and include it in the function that gets called?

Cense

use method with userinfo ... NSNotificationCenter.defaultCenter().postNotificationName("hideSpinner", object: nil, userInfo: yourvalue) – Logistic

hm ok, and how can I fetch this yourValue in the function that gets called on that notification (in showSpinningWheel)? – Cense

using .userinfo like notification.userinfo – Logistic

Answer 1

Swift 2.0

Pass info using userInfo which is an optional Dictionary of type [NSObject : AnyObject]?

let imageDataDict:[String: UIImage] = ["image": image]

// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
// `default` is now a property, not a method call

// Register to receive notification in your class
NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

// handle notification
// For swift 4.0 and above put @objc attribute in front of function Definition  
func showSpinningWheel(_ notification: NSNotification) {
    if let image = notification.userInfo?["image"] as? UIImage {
        // do something with your image   
    }
}

Swift 3.0, 4.0, 5.0 version and above

The userInfo now takes [AnyHashable: Any]? as an argument, which we provide as a dictionary literal in Swift

let imageDataDict:[String: UIImage] = ["image": image]

// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
// `default` is now a property, not a method call

// Register to receive notification in your class
NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

// handle notification
// For swift 4.0 and above put @objc attribute in front of function Definition  
func showSpinningWheel(_ notification: NSNotification) {
    if let image = notification.userInfo?["image"] as? UIImage {
        // do something with your image   
    }
}

NOTE: Notification “names” are no longer strings, but are of type Notification.Name, hence why we are using NSNotification.Name(rawValue: "notificationName") and we can extend Notification.Name with our own custom notifications.

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

// and post notification like this
NotificationCenter.default.post(name: .myNotification, object: nil)

Yclept

Answer 2

For Swift 3

let imageDataDict:[String: UIImage] = ["image": image]

  // post a notification
  NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
  // `default` is now a property, not a method call

 // Register to receive notification in your class
 NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

 // handle notification
 func showSpinningWheel(_ notification: NSNotification) {
        print(notification.userInfo ?? "")
        if let dict = notification.userInfo as NSDictionary? {
            if let id = dict["image"] as? UIImage{
                // do something with your image
            }
        }
 }

For Swift 4

let imageDataDict:[String: UIImage] = ["image": image]

  // post a notification
  NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
  // `default` is now a property, not a method call

 // Register to receive notification in your class
 NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

 // handle notification
 @objc func showSpinningWheel(_ notification: NSNotification) {
        print(notification.userInfo ?? "")
        if let dict = notification.userInfo as NSDictionary? {
            if let id = dict["image"] as? UIImage{
                // do something with your image
            }
        }
 }

Saying

Worked for me Swift 4 – Calabria

Answer 3

Hello @sahil I update your answer for swift 3

let imageDataDict:[String: UIImage] = ["image": image]

  // post a notification
  NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict) 
  // `default` is now a property, not a method call

 // Register to receive notification in your class
 NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

 // handle notification
 func showSpinningWheel(_ notification: NSNotification) {
        print(notification.userInfo ?? "")
        if let dict = notification.userInfo as NSDictionary? {
            if let id = dict["image"] as? UIImage{
                // do something with your image
            }
        }
 }

Hope it's helpful. Thanks

Reboant

should be notification.userinfo, not notification.object – Coen

If you are receiving object/dictionary from objective-c class/notification you must use .object. If you are receiving object from Swift notification use .userInfo. Track you notification if it is .object or .userInfo with: func observerNotification(notification: NSNotification){ print("Notification Received :", notification) } – Appeasement

Make sure if you are sending across threads that you set up the observer on that key before you post to that notification key. You may be more familiar with the terms listener and event. – Honkytonk

Answer 4

This is what worked for me in Swift 5

NotificationCenter.default.addObserver(self,
                                       selector: #selector(handleMassage),
                                       name: Notification.Name("NotificationName"),
                                       object: nil)

The method that handles the notification:

    @objc func handleMassage(notification: NSNotification) {
    if let dict = notification.object as? NSDictionary {
        if let myMessage = dict["myMessage"] as? String{
            myLabel.text = myMessage
        }
    }
}

I posted it like this:

let dic = ["myMessage": "testing"]
NotificationCenter.default.post(name: Notification.Name("NotificationName"), object: dic)

Primogenitor

Answer 5

Swift 5.5 with avoid #selector():

First of all, declare the name:

extension Notification.Name {
    static let prettyName = Notification.Name("MyPrettyName")
}

Next is to add observer (take care with queue):

// For example transferred data should implement protocol
protocol PrettyDelegate {
    func doSomethingAwesome()
}

// Here is the way how we can subscribe as observer
NotificationCenter.default.addObserver(forName: .prettyName, object: nil, queue: nil) { [weak self] notif in
    guard let self = self else { return } // Because self used more than once
    if let userInfo = notif.userInfo,
       let delegate = userInfo["pretty"] as? PrettyDelegate {
        self.delegate = delegate
    }
    
    self.makePretty() // Here we can do anything
}

Finally, we can post the notification from another object

// Here I'll illustrate how to pass optional value as userInfo
var userInfo: [AnyHashable : Any]?
if let prettyDelegate = self as? PrettyDelegate {
    userInfo = ["pretty": prettyDelegate]
}
NotificationCenter.default.post(name: .prettyName, object: nil, userInfo: userInfo)
    

NOTE: Do NOT forget to remove the observer, when you will not need it anymore.

Tympanitis

Answer 6

this is how I implement it .

let dictionary = self.convertStringToDictionary(responceString)            
     NotificationCenter.default.post(name: NSNotification.Name(rawValue: "SOCKET_UPDATE"), object: dictionary)

Saratov

Answer 7

In swift 4.2 I used following code to show and hide code using NSNotification

 @objc func keyboardWillShow(notification: NSNotification) {
    if let keyboardSize = (notification.userInfo? [UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue {
        let keyboardheight = keyboardSize.height
        print(keyboardheight)
    }
}

Dyna