先感谢您！！

override func viewDidLoad() {
    super.viewDidLoad()

    var user: String?
    user = UserDefaults.standard.value(forKey: "loginSuccessfull") as? String

    if user == "true" {
        let vc = self.storyboard?.instantiateViewController(withIdentifier: "SecondView") as UIViewController!
        self.show(vc!,sender: vc)
    }

    // Do any additional setup after loading the view,typically from a nib.
}