Swift 3 KVO to observe change in NSMutableSet (add, remove, modify item)

Question

I'm develop an app which has an set of unique string. I have a function to add, remove, modify item in the NSMutableSet. I want to use KVO (key value observer) to observe whenever the set has change (add, remove, modify item).

Here's my code:

dynamic var barCodeSet = NSMutableSet()

in viewDidload I add observe:

    override func viewDidLoad() {
        super.viewDidLoad()
        
        addObserver(self, forKeyPath: #keyPath(barCodeSet), options: [.old,.new,.initial], context: nil)
        
    }

And this is my observe function:

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == #keyPath(barCodeSet) {
            print(barCodeSet.count)
            for barcode in barCodeSet {
                print(barcode)
            }
        }
    }

I don't know why the KVO is not working. How can I modify the code so that we can get notify when set items change?

Possible duplication of http://stackoverflow.com/questions/6403570/key-value-observing-an-nsmutableset — Aruna Mudnoor, Nov 04 '16 at 12:00

Marcus · Accepted Answer · 2016-11-04T12:05:34.303

1

Assuming you do not need to use NSMutableSet, you could use a didSet clause in the variable declaration. try the following in a playground:

import UIKit

class myClass {

    init() {

    }

    dynamic var barCodeSet: Set<String> = Set<String>() {
        didSet {
            print(barCodeSet.count)
            for barcode in barCodeSet {
                print(barcode)
            }
        }
    }
}

let thisClass = myClass()

thisClass.barCodeSet = ["Apples", "Bananas", "Oranges"]
thisClass.barCodeSet.insert("Grapes")

Whenever you set the value of barCodeSet, its count and contents are printed to the console.

edited Nov 04 '16 at 12:05

answered Nov 04 '16 at 11:47

Marcus

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Seem the didset will not work on array or set. For ex when we add new item to set – Lê Khánh Vinh Nov 04 '16 at 11:49
It works if you use a Swift Set, for example Set. Do you need to use NSMutableSet? – Marcus Nov 04 '16 at 11:59
I need add unique item type String to the set if there is new data on the server. Can we use Set for this task? – Lê Khánh Vinh Nov 04 '16 at 12:02
I've edited my code above. Run it in a playground and you should see didSet outputting to the console. – Marcus Nov 04 '16 at 12:06
Work like a charm thanks a lot. So didSet is only available for Swift? Do you know any alternative for Objective C? – Lê Khánh Vinh Nov 04 '16 at 12:21
I think that you are looking at standard KVO for objective C, but there appear to be lots of discussions on SO on this topic. – Marcus Nov 04 '16 at 12:25
beside the didSet. Do know thing my KVO approach as from the question should be good to dig through? any change need to be made inorder for these block to work? – Lê Khánh Vinh Nov 04 '16 at 12:29

Swift 3 KVO to observe change in NSMutableSet (add, remove, modify item)

1 Answers1