-[NSConcreteNotification count]: unrecognized selector sent to instance 0x2816dd380

user_3066714 0
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Took me an hour to figure this iOS crash out, posting the solution in case it helps. You might have a different value other than count after NSConcreteNotification in your crash.

I was crashing on accessing an array.count, which is why it's count in my case:

    @objc fileprivate func loadParts(constraints: [NSLayoutConstraint]? = nil) {
        assert(Thread.current.isMainThread)
        var constraints = constraints ?? [NSLayoutConstraint]()
        ...
        let cCount = constraints.count

I could not for the life of me see how it could crash on constraints.count as the array is guaranteed to exist.

ios
1 Answers

I was wiring this function up to a Notification like this:

NotificationCenter.default.addObserver(self, selector: #selector(self.loadParts), name: UIDevice.batteryStateDidChangeNotification, object: nil)

If you look at the documentation for addObserver, it says the function must have exactly one parameter which is a Notification. What was happening was that my function was being called with a Notification, but my code expected it to be an array.

The fix was to create a new function that simply called the function I wanted (loadParts), and have the Notification hit that instead:

    NotificationCenter.default.addObserver(self, selector: #selector(self.loadPartsNotification(_:)), name: UIDevice.batteryStateDidChangeNotification, object: nil)

    ...

    @objc fileprivate func loadPartsNotification(_ notification: Notification) {
        self.loadParts()
    }
    
    fileprivate func loadParts(constraints: [NSLayoutConstraint]? = nil) {
    ...
user_30667140
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