Why does changing stepper value cause code to crash in Xcode? - ios

Question

I am attempting to create an app in Xcode. I have added a stepper and a text box, and added outlets to the ViewController for these. When making an action to capture the change in stepper value, my code crashes upon clicking the stepper if I include any code at all in my changing value function.
Here is my ViewController.swift file:
import UIKit
class ViewController: UIViewController {
#IBAction func stepperValueChanged(_ sender: UIStepper) {
let newVal = Int(sender.value).description
self.valueLabel.text = String(newVal)
}
#IBOutlet weak var stepper: UIStepper!
#IBOutlet weak var generate: UIButton!
#IBOutlet weak var valueLabel: UILabel!
#IBAction func buttonClicked(_ sender: UIButton) {
}
override func viewDidLoad() {
super.viewDidLoad()
}
}
It says my main thread sends signal SIGABRT in the AppDelegate file, which I have not modified:
import UIKit
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
return true
}
// MARK: UISceneSession Lifecycle
func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
// Called when a new scene session is being created.
// Use this method to select a configuration to create the new scene with.
return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
}
func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
// Called when the user discards a scene session.
// If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
// Use this method to release any resources that were specific to the discarded scenes, as they will not return.
}
}
This is the console output:
2019-12-18 00:16:00.234618-0600 core[95979:16142343] -[NSLayoutConstraint setText:]: unrecognized selector sent to instance 0x600002c202d0
2019-12-18 00:16:00.240568-0600 core[95979:16142343] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSLayoutConstraint setText:]: unrecognized selector sent to instance 0x600002c202d0'
*** First throw call stack:
(
0 CoreFoundation 0x00007fff23c4f02e __exceptionPreprocess + 350
1 libobjc.A.dylib 0x00007fff50b97b20 objc_exception_throw + 48
2 CoreFoundation 0x00007fff23c6ff94 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
3 CoreFoundation 0x00007fff23c53dac ___forwarding___ + 1436
4 CoreFoundation 0x00007fff23c55f38 _CF_forwarding_prep_0 + 120
5 core 0x000000010c9fd5f3 $s4core14ViewControllerC19stepperValueChangedyySo9UIStepperCF + 643
6 core 0x000000010c9fd714 $s4core14ViewControllerC19stepperValueChangedyySo9UIStepperCFTo + 68
7 UIKitCore 0x00007fff47850dfa -[UIApplication sendAction:to:from:forEvent:] + 83
8 UIKitCore 0x00007fff4722ac22 -[UIControl sendAction:to:forEvent:] + 223
9 UIKitCore 0x00007fff4722af6c -[UIControl _sendActionsForEvents:withEvent:] + 398
10 UIKitCore 0x00007fff47be4a72 -[UIStepperHorizontalVisualElement _updateCount:] + 376
11 UIKitCore 0x00007fff47be473f -[UIStepperHorizontalVisualElement endTrackingWithTouch:withEvent:] + 33
12 UIKitCore 0x00007fff47258372 -[UIStepper endTrackingWithTouch:withEvent:] + 95
13 UIKitCore 0x00007fff47229e95 -[UIControl touchesEnded:withEvent:] + 427
14 UIKitCore 0x00007fff4788bc1d -[UIWindow _sendTouchesForEvent:] + 2604
15 UIKitCore 0x00007fff4788d524 -[UIWindow sendEvent:] + 4596
16 UIKitCore 0x00007fff47868427 -[UIApplication sendEvent:] + 356
17 UIKitCore 0x00007fff478e987e __dispatchPreprocessedEventFromEventQueue + 6847
18 UIKitCore 0x00007fff478ec344 __handleEventQueueInternal + 5980
19 CoreFoundation 0x00007fff23bb2221 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
20 CoreFoundation 0x00007fff23bb214c __CFRunLoopDoSource0 + 76
21 CoreFoundation 0x00007fff23bb1924 __CFRunLoopDoSources0 + 180
22 CoreFoundation 0x00007fff23bac62f __CFRunLoopRun + 1263
23 CoreFoundation 0x00007fff23babe16 CFRunLoopRunSpecific + 438
24 GraphicsServices 0x00007fff38438bb0 GSEventRunModal + 65
25 UIKitCore 0x00007fff4784fb48 UIApplicationMain + 1621
26 core 0x000000010c9ff63b main + 75
27 libdyld.dylib 0x00007fff51a1dc25 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)
What could be the problem?

Answer 1

I have a quick look in debug console and I found something wrong. it's related to constraints, You are trying to set text in NSLayoutConstraint, Which is logically incorrect. Because NSLayoutConstraint doesn't have any property to set text.
Please review your code once and find out where you are trying to do like [NSLayoutConstraint setText:] or you can share your code with me, I can have a look on your code and fix it for you.