KV观察器

let kvObserver = KVObserver()
let observedObject = ObservedObject()

/* Start observing observedObject */ 
let observingId = kvObserver.observe(object: observedObject, keyPath: #keyPath(ObservedObject.observableProperty), kvoOptions: [.initial], dispatchType: .asyncOnMainQueueDirectInitial, handler: { [weak self] change in
   /* Handle changes here */
})

/* End observing observedObject */ 
kvObserver.stopObserving(id: observingId)
/* Or, stop observing everything */
kvObserver.stopObservingEverything()