ios - 为什么 Firebase Auth Signin 和登录 segue 被调用两次

Question

我正在使用 Firebase Auth 登录我的应用程序，然后启动到主屏幕的 segue。出于某种原因，当登录时，Segue 似乎发生了两次，而当用户已经登录时，segue 按预期发生了一次。我不确定问题出在哪里，这是登录代码:

func login() {
    Auth.auth().signIn(withEmail: emailInput.text!, password: passwordInput.text!) { (user, error) in
        if let user = user {
            print("User is signed in.")
            let verified = Auth.auth().currentUser?.isEmailVerified
            if verified == true {
                self.ref = Database.database().reference()

                CurrentUser.shared.getCurrentUserInfo()
                self.userName = CurrentUser.shared.username

                print("loginSegue")
                self.performSegue(withIdentifier: "loginToHome", sender: nil)
                print("loginSegue2")

            } else ...

在控制台上，loginSegue 打印仅显示一次，而在应用程序中它似乎发生两次，就像在这个 gif 中一样:

我不认为这是 Home View Controller 中的问题，因为当用户已经登录并且应用程序从初始 View Controller 启动 segue 时，它​​不会发生，这里是自动登录代码，它似乎工作正常:

 override func viewWillAppear(_ animated: Bool) {
    Auth.auth().addStateDidChangeListener { auth, user in
        if let user = user {
            print("User is signed in.")
            let verified = Auth.auth().currentUser?.isEmailVerified
            let user_id = Auth.auth().currentUser?.uid
            if verified == true {
                self.ref = Database.database().reference()

                let usersReference = self.ref.child("users").child(user_id!)

                usersReference.observeSingleEvent(of: .value, with: { (snapshot) in
                    // Get user value
                    let value = snapshot.value as? NSDictionary
                    let name = value?["username"] as? String ?? ""
                    self.userName = name
                    self.performSegue(withIdentifier: "alreadyLoggedIn", sender: nil)

                })
            } else {

            }
        } else {
            print("User is signed out. (StartViewController)")
        }
    }
}

为什么这会正常工作，但登录转场似乎发生了两次？

Answer 1

像这样

Auth.auth().addStateDidChangeListener { auth, user in

当登录验证发生时触发，并从这部分引起 segue

usersReference.observeSingleEvent(of: .value, with: { (snapshot) in
   // Get user value
   let value = snapshot.value as? NSDictionary
   let name = value?["username"] as? String ?? ""
   self.userName = name
   self.performSegue(withIdentifier: "alreadyLoggedIn", sender: nil) 
})