ios - 重新启动应用程序 swift 4 时，UserDefaults 有时不保留保存的值

Question

我正在保存 Storyboard名称和当前的 View Controller ，以便当用户在主屏幕上点击“恢复”(HomeScreenVC 中的 resumeButtonWasPressed)时，他们可以立即返回到之前查看的 View 。每次我在类中设置值后打印这些值时，都会打印出正确的值，例如“Chapter1”“Page2”。然而，当用户按主屏幕上的“恢复”时，只有一定比例的时间会进入正确的 View 。要保存的正确值在类本身中打印出来，但是当我从 HomeScreenVC 中的 UserDefaults 检索值时，有时会打印出错误的 Storyboard 和 viewController 。我的代码如下。

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    _ = UserDefaults.standard
    _ = ["strength" : 0]
    _ = ["intellect" : 0]
    _ = ["charisma" : 0]
    _ = ["name" : ""]
    _ = ["storyBoard" : "Main"]
    _ = ["viewController" : "HomeScreenVC"]

    // Override point for customization after application launch.
    return true
}

以下是我的 HomeScreenVC 代码，删除了非必需内容:

class HomeScreenVC: UIViewController {
    let defaults = UserDefaults.standard

    @IBAction func resumeButtonWasPressed(_ sender: Any) {
        let sb = defaults.string(forKey: "storyBoard")
        let vc = defaults.string(forKey: "viewController")
        let storyBoard : UIStoryboard = UIStoryboard(name: sb!, bundle: nil)
        let newViewController = storyBoard.instantiateViewController(withIdentifier: vc!)
        self.navigationController?.pushViewController(newViewController, animated: true)
    }

    override func viewDidAppear(_ animated: Bool) {
        let sb = defaults.string(forKey: "storyBoard")
        let vc = defaults.string(forKey: "viewController")
        print(sb!)
        print(vc!)
    }
}

这是我的 infoScreen VC，删除了非必需品:

class InfoScreenVC: UIViewController {
    let defaults = UserDefaults.standard

    override func viewDidAppear(_ animated: Bool) {
        let storyboard = self.storyboard?.value(forKey: "name")
        UserDefaults.standard.set(storyboard, forKey: "storyBoard") // save to user defaults
        let newViewController = self.restorationIdentifier
        UserDefaults.standard.set(newViewController, forKey: "viewController")
    }
}

这是我的 page1VC，删除了非必需品:

class Page1VC: UIViewController {
    let defaults = UserDefaults.standard

    override func viewDidAppear(_ animated: Bool) {
        let storyboard = self.storyboard?.value(forKey: "name")
        UserDefaults.standard.set(storyboard, forKey: "storyBoard") // save to user defaults                
        let newViewController = self.restorationIdentifier
        UserDefaults.standard.set(newViewController, forKey: "viewController")
    }
}

这是我的 Page2VC，删除了非必需品:

class Page2VC: UIViewController {
    let defaults = UserDefaults.standard

    override func viewDidAppear(_ animated: Bool) {
        let storyboard = self.storyboard?.value(forKey: "name")
        UserDefaults.standard.set(storyboard, forKey: "storyBoard") // save to user defaults
        let newViewController = self.restorationIdentifier
        UserDefaults.standard.set(newViewController, forKey: "viewController")
    }
}

Answer 1

尝试将 applicationDidFinishLaunchingWithOptions 中的代码替换为:

let defaults = UserDefaults.standard
defaults.set(0, forKey: "strength")
defaults.set(0, forKey: "intellect")
defaults.set(0, forKey: "charisma")
defaults.set("", forKey: "name")
defaults.set("Main", forKey: "storyBoard")
defaults.set("HomeScreenVC", forKey: "viewController")

// Override point for customization after application launch.
return true

编辑

此外，您还应该检查 applicationDidFinishLaunchingWithOptions，如果 UserDefaults 键已设置，并且仅在此时未设置时才设置它们。例如:

let defaults = UserDefaults.standard
if defaults.object(forKey: "storyBoard") == nil { // you could use any other key that you use in the app
    defaults.set(0, forKey: "strength")
    defaults.set(0, forKey: "intellect")
    defaults.set(0, forKey: "charisma")
    defaults.set("", forKey: "name")
    defaults.set("Main", forKey: "storyBoard")
    defaults.set("HomeScreenVC", forKey: "viewController")
}

否则它们会在每次应用启动时被覆盖。