Checking if a value is changed using KVO in Swift 3

Question

I would like to know when a set of properties of a Swift object changes. Previously, I had implemented this in Objective-C, but I\'m having some difficulty converting it to

Answer 1

My original 'second attempt' contains a bug that will fail to detect when a value changes to or from nil. The first attempt can actually be fixed once one realizes that all values of 'change' are NSObject:

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    let oldValue: NSObject? = change?[.oldKey] as? NSObject
    let newValue: NSObject? = change?[.newKey] as? NSObject
    if newValue != oldValue {
        edit()
    }
}

or a more concise version if you prefer:

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if change?[.newKey] as? NSObject != change?[.oldKey] as? NSObject {
        edit()
    }
}