How to access a Dictionary passed via NSNotification, using Swift

Question

I have code that sends a notification (where serialNumber is a String):

  var dataDict = Dictionary<String, String>()
  dataDict["Identity"] = serialNumber
  dataDict["Direction"] = "Add"
            NSNotificationCenter.defaultCenter().postNotificationName("deviceActivity", object:self, userInfo:dataDict)

And code that receives this notification:

  func deviceActivity(notification: NSNotification) {

     // This method is invoked when the notification is sent
     // The problem is in how to access the Dictionary and pull out the entries
  }

I've tried a variety of code to accomplish this, with no success:

let dict = notification.userInfo
let dict: Dictionary<String, String> = notification.userInfo
let dict: Dictionary = notification.userInfo as Dictionary

And while some of my attempts satisfy the compiler, none have yielded actual Strings when trying to access what has been extracted as a Dictionary:

let sn : String = dict["Identity"]!
let sn : String = dict.valueForKey("Identity") as String
let sn : String = dict.valueForKey("Identity")

So the question is this: How do I write Swift code to extract an object, in this case a Dictionary, that was passed via a notification, and access the component parts of that object (in this case the keys and values)?

score 42 · Answer 1 · answered Jul 22 '14 at 16:33

42

As notification.userInfo type is AnyObject ayou must downcast it to appropriate dictionary type.

After exact type of dictionary is known you don't need to downcast values you get from it. But you may want to check if values are actually present in dictionary before using them:

// First try to cast user info to expected type
if let info = notification.userInfo as? Dictionary<String,String> {
  // Check if value present before using it
  if let s = info["Direction"] {
    print(s)
  }
  else {
    print("no value for key\n")
  }
}
else {
  print("wrong userInfo type")
}

answered Jul 22 '14 at 16:33

Vladimir

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always hit's the print("wrong userInfo type") - in swift 2 – Async- Dec 28 '15 at 12:27
@Async- It works for me in playground. You need to make sure that all your keys and values are strings however. If you have different types you will need to change types in 1st cast – Vladimir Dec 28 '15 at 15:49
sorry, yes it works - after reset content of simulator, clean and build it works! – Async- Jan 06 '16 at 08:53
Works great! Thank you. – Christopher Wade Cantley Nov 16 '16 at 21:51
Value of type 'UNNotification' has no member 'userInfo' in 4.9.19 – ScottyBlades Apr 10 '19 at 05:20
@ScottyBlades UNNotification is a different API from NSNotification – Vladimir Apr 10 '19 at 14:14
@Vladimir my bad! – ScottyBlades Apr 11 '19 at 08:46

score 12 · Answer 2 · edited Jun 03 '15 at 08:47

12

You should use structure like [NSObject : AnyObject] and retrieve value as from NSDictionary yourLet[key]

func keyboardWillShown(notification : NSNotification){
    let tmp : [NSObject : AnyObject] = notification.userInfo!
    let duration : NSNumber = tmp[UIKeyboardAnimationDurationUserInfoKey] as NSNumber
    let scalarDuration : Double = duration.doubleValue
}

edited Jun 03 '15 at 08:47

Pang

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answered Sep 23 '14 at 05:45

Oleg Kohtenko

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How to access a Dictionary passed via NSNotification, using Swift

2 Answers2