Swift App继续与Firebase签约

Question

问题：在应用终止时保持登录状态。用户在应用程序最小化时登录，但是当我终止应用程序时，用户不会保持登录状态。任何人都可以看到问题吗？

- 我不希望每次打开应用程序时都要求用户注册

ViewController.swift （＆＃34; TEST2＆＃34;永远不会被执行）

import UIKit
import Firebase
import FirebaseDatabase
import KeychainSwift

class ViewController: UIViewController {

    @IBOutlet weak var emailField: UITextField!
    @IBOutlet weak var passwordField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()

    }

    override func viewDidAppear(_ animated: Bool) {

        print("TEST1")

        let keyChain = DataService().keyChain
        if keyChain.get("uid") != nil {
            performSegue(withIdentifier: "SignIn", sender: nil)
             print("TEST2")
        }
    }

    func CompleteSignIn(id: String){
        let keyChain = DataService().keyChain
        keyChain.set(id , forKey: "uid")
    }

    @IBAction func SignIn(_ sender: Any){
        if let email = emailField.text, let password = passwordField.text {
            FIRAuth.auth()?.signIn(withEmail: email, password: password) { (user, error) in
                if error == nil {
                    self.CompleteSignIn(id: user!.uid)
                    self.performSegue(withIdentifier: "SignIn", sender: nil)
                } else {
                    FIRAuth.auth()?.createUser(withEmail: email, password: password) { (user, error) in
                        if error != nil {
                            print("cant sign in user")
                        } else {
                            self.CompleteSignIn(id: user!.uid)
                            self.performSegue(withIdentifier: "SignIn", sender: nil)
                        }
                    }
                }
            }
        }
    }
}

DataService.swift

import Foundation
import Firebase
import FirebaseDatabase
import KeychainSwift

let DB_BASE = FIRDatabase.database().reference()

class DataService {
    private var _keyChain = KeychainSwift()
    private var _refDatabase = DB_BASE

    var keyChain: KeychainSwift {
        get {
            return _keyChain
        } set {
            _keyChain = newValue
        }
    }
}