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I'm trying to learn how to use Combine in an AppKit app I'm working on. I found an Apple Developer article that explains pretty much exactly what I'm trying to achieve, delaying input from an NSTextField with the .debounce operator. (https://developer.apple.com/documentation/combine/receiving-and-handling-events-with-combine) Unfortunately it doesn't seem to be working for me. I have created a function in a NSTableCellView subclass that gets called as part of the cell's configuration which looks like:     private func watchForSearchTextEntries() { print("Setting up search text observer") let sub = NotificationCenter.default .publisher(for: NSControl.textDidChangeNotification, object: searchTermText) .map( { ($0.object as! NSTextField).stringValue } ) .sink(receiveCompletion: { print ($0) }, receiveValue: { print ($0) })  } When I run the app and type in that field, nothing gets printed to the Console. As a test, I also tried adding a NotificationCenter observer that calls a method to print out the notification's object. NotificationCenter.default.addObserver(self, selector: #selector(receivedTextChangeNotification(_:)), name: NSControl.textDidChangeNotification, object: searchTermText) That works as expected. So what's going on with my attempted use of Combine?

I've experienced repeatable crashes in an iOS app using KVO, and I'm wondering if anyone else is having the same issue. This is in Xcode 11 beta 7 running in Catalina beta 7 on the iPhone XR simulator. My project targets iOS 11 as a minimum deployment, but I was able to reproduce this issue in a very simple project that targets iOS 13.Here's the pertinent code from my simple demo:Create a class to observe:class ObservableObject: NSObject { dynamic var purchaseInProgress = false dynamic var wasPurchased = false var name = "" init(name: String) { self.name = name }}In a view controller, add an iVar for a strong reference to an observers array, and an array of observable objects: var observers = [NSKeyValueObservation]() var products = [ObservableObject]()Be sure to initialized the products array with some values: override func viewDidLoad() { super.viewDidLoad() products.append(ObservableObject(name: "Hot Fudge Sundae")) products.append(ObservableObject(name: "Deluxe Cheeseburger")) }Then add an outlet to a button that can trigger the action, and a method that should be called when an object is changed: @IBAction func setupObservers() { let purchaseProgressKeyPath = \ObservableObject.purchaseInProgress let wasPurchasedKeyPath = \ObservableObject.wasPurchased for product in products { self.observers.append(product.observe(purchaseProgressKeyPath, changeHandler: { (changedProduct, change) in self.productWasChanged(changedProduct) })) self.observers.append(product.observe(wasPurchasedKeyPath, changeHandler: { (changedProduct, change) in self.productWasChanged(changedProduct) })) } } @objc func productWasChanged(_ product: ObservableObject) { }Run the project and watch it crash with:Fatal error: Could not extract a String from KeyPath Swift.ReferenceWritableKeyPath<KVOCrash.ObservableObject, Swift.Bool>: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang_overlay_Foundation_Sim/swiftlang-1100.2.259.50/swift/stdlib/public/Darwin/Foundation/NSObject.swift, line 155At least that's my result. I hope this is something Apple needs to, and will, fix. This example is borrowed from more complex code that's working just fine in Xcode 10 but crashing in the Xcode 11 beta 7.