Ios ViewController首次使用后未更改

嗨，我只想在第一次使用时显示视图控制器（即：有人第一次启动应用程序，以后再也不显示）

我认为我有正确的代码，但由于某些原因，它只是不工作。有人知道为什么吗

AppDelegate.swift

import UIKit
import CoreData

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    let userDefaults = UserDefaults.init()

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        userDefaults.set(true, forKey: "isFirstTime")
        userDefaults.set("RealmNotChosenOrSuggested", forKey: "RegionPreference")
        userDefaults.set([], forKey: "PreferredRealms")

        // Not using Storyboard instantiation code
        window = UIWindow(frame:UIScreen.main.bounds) //canvas
        window?.makeKeyAndVisible()

        if (userDefaults.bool(forKey: "isFirstTime")){
            userDefaults.set(false, forKey: "isFirstTime")
            window?.rootViewController = StartupViewController()
        } else{
            window?.rootViewController = DashboardViewController()
        }
        return true
    }

StartupViewController.swift

class StartupViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
    }

DashboardViewController.swift

import UIKit

class DashboardViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .blue
    }

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因为每次应用程序打开它运行时，您都会覆盖第一行中的键

isFirstTime

 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
  //  userDefaults.set(true, forKey: "isFirstTime") // firs line comment it


if !(userDefaults.bool(forKey: "isFirstTime")){
    userDefaults.set(true, forKey: "isFirstTime")
    userDefaults.set("RealmNotChosenOrSuggested", forKey: "RegionPreference")
    userDefaults.set([], forKey: "PreferredRealms")
    window?.rootViewController = StartupViewController()
} else{
    window?.rootViewController = DashboardViewController()
}

---

从默认值读取密钥时，任何bool的默认值都为false