NSKeyValueObservation 不起作用，Swift 4

Question

当变量在单例的共享实例上发生更改时，我应该如何正确设置以接收通知？目前，该块从未被触发。

class MyViewController: UIViewController {
    private var observer: NSKeyValueObservation?

    func configureKVO() {
        observer = MySingleton.shared.observe(\.shouldFetchDataFromServer) { (manager, change) in
            print("Changed: \(manager.shouldFetchDataFromServer)")
        }
        MySingleton.shared.shouldFetchDataFromServer = false
        MySingleton.shared.shouldFetchDataFromServer = true
    }
}

class MySingleton: NSObject {
    static let shared = MySingleton()
    @objc var shouldFetchDataFromServer: Bool = false
}

Answer 1

将'dynamic'关键字添加到shouldFetchDataFromServer的声明中，它应该可以工作。