Question

我希望我第一次登录时会出现类似教程的内容。

但是它说：

二进制运算符'=='不能应用于类型为'String？'的操作数和“布尔”

override func viewDidLoad() {
    super.viewDidLoad()
    let checkForFirstTimeLaunch = UserDefaults.standard.string(forKey: "Flag")

    if checkForFirstTimeLaunch == false {
        print("First time launch")

        //if user launches app for the first time, it will go here
        let PageViewController = self.storyboard?.instantiateViewController(withIdentifier: "PageViewController") as! PageViewController

        self.present(PageViewController, animated: true)
    } else {
        //otherwise, it will go here
        let HomeViewController = self.storyboard?.instantiateViewController(withIdentifier: "HomeViewController") as! HomeViewController

        self.present(HomeViewController, animated: true)
    }
}

Answer 1

使用此方法首次启动应用 func isAppAlreadyLaunchedOnce（）-> Bool { let defaults = NSUserDefaults.standardUserDefaults（）

if let isAppAlreadyLaunchedOnce = defaults.stringForKey("isAppAlreadyLaunchedOnce"){
    println("App already launched")
    return true
}else{
    defaults.setBool(true, forKey: "isAppAlreadyLaunchedOnce")
    println("App launched first time")
    return false
}

}

Answer 2

正如其他人所述，您只能比较String-String或Bool-Bool。在这种情况下-对于标志-最好使用Bool

此外，用户首次启动应用后，还必须保存true。

override func viewDidLoad() {
    super.viewDidLoad()
    let checkForFirstTimeLaunch = UserDefaults.standard.bool(forKey: "Flag") // default is false

    if checkForFirstTimeLaunch == false {
        print("First time launch")
        UserDefaults.standard.set(true, forKey: "Flag") // save `true` to go to the else branch the next time
        //if user launches app for the first time, it will go here
        let PageViewController = self.storyboard?.instantiateViewController(withIdentifier: "PageViewController") as! PageViewController

        self.present(PageViewController, animated: true)
    } else {
        //otherwise, it will go here
        let HomeViewController = self.storyboard?.instantiateViewController(withIdentifier: "HomeViewController") as! HomeViewController

        self.present(HomeViewController, animated: true)
    }
}

但是，从逻辑角度讲，默认情况下， FirstTimeLaunch 应该为 true 。在这种情况下，请在使用前注册键值对。在更改之前，将考虑已注册的默认值：

override func viewDidLoad() {
    super.viewDidLoad()
    let userDefaults = UserDefaults.standard
    userDefaults.register(defaults: ["firstLaunch" : true])

    let isFirstLaunch = userDefaults.bool(forKey: "firstLaunch")

    if isFirstLaunch {
        print("First time launch")
        userDefaults.set(false, forKey: "firstLaunch") // save `false` to go to the else branch the next time
        //if user launches app for the first time, it will go here
        let PageViewController = self.storyboard?.instantiateViewController(withIdentifier: "PageViewController") as! PageViewController

        self.present(PageViewController, animated: true)
    } else {
        //otherwise, it will go here
        let HomeViewController = self.storyboard?.instantiateViewController(withIdentifier: "HomeViewController") as! HomeViewController

        self.present(HomeViewController, animated: true)
    }
}

将UserDefaults中的字符串与Bool进行比较时出错

2 个答案: