Object X of class Y does not implement methodSignatureForSelector in Swift

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Don’t think of NSObject as an Objective-C class, think of it as a Cocoa/Foundation class. Even though you’re using Swift instead of Objective-C, you’re still using all the same frameworks.

Two options: (1) add the dynamic attribute to the function you want to reference as a selector:

    dynamic func timerTick() {
        self.angerLevel++
        print("Angry! \(self.angerLevel)")
    }

Or (2) declare Person as a subclass of NSObject, then just call super.init() at the beginning of your initializer:

class Person: NSObject {
    var timer = NSTimer()
    var angerLevel = 0

    func startTimer() {
        print("starting timer")
        timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "timerTick", userInfo: nil, repeats: true)
    }

    func timerTick() {
        self.angerLevel++
        print("Angry! \(self.angerLevel)")
    }

    override init() {
        super.init()
        self.startTimer()
    }
}

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