ios - 检测首次启动时出错(Swift)

Question

我正在尝试检测该应用程序是否是首次打开。我已将这段代码放入我的 ViewController 的 viewDidLoad()

override func viewDidLoad() {
        super.viewDidLoad()

        let launchedBefore = UserDefaults.standard.bool(forKey: "launchedBefore")
        if launchedBefore  {
            performSegue(withIdentifier: "toMainController", sender: self)
            print("launchedBefore")
        } else {
            performSegue(withIdentifier: "toTutorialController", sender: self)
            UserDefaults.standard.set(true, forKey: "launchedBefore")
            print("not launchedBefore")

        }
    }

但是，无论何时启动 ViewController，都不会执行任何转场。但是我告诉它打印的内容被打印了。如果重要的话，segue "toMainController" 转到的 View 是一个 UITabViewController，而 segue "toTutorialController" 转到的 View 只是一个 UIViewController。

有没有人知道为什么这不起作用？

更新

我发现了这个错误

2017-06-30 09:02:32.984 AppName[29732:24744712] Warning: Attempt to present on < AppName.ViewController: 0x7fcbfa908ed0> whose view is not in the window hierarchy!

Answer 1

先保存到userDefault，然后执行segue:-

override func viewDidLoad() {
        super.viewDidLoad()

        let launchedBefore = UserDefaults.standard.bool(forKey: "launchedBefore")
        if launchedBefore  {
            performSegue(withIdentifier: "toMainController", sender: self)
            print("launchedBefore")
        } else {
            UserDefaults.standard.set(true, forKey: "launchedBefore")
            performSegue(withIdentifier: "toTutorialController", sender: self)
            print("not launchedBefore")
        }
    }