Swift 我怎样才能阻止斯威夫特的一个赛格？

我有一个登录场景，当用户单击“登录”按钮时，它会切换到另一个场景，但是，当用户的电子邮件和密码不正确时，我试图阻止它发生。我正在使用Firebase，下面的这个函数检查用户名和密码是否正确，但我想在用户名和密码不正确时阻止这个过程

 func userLogin (user: String!, pass: String!){
    ref.authUser(user, password: pass,
                 withCompletionBlock: { error, authData in
                    if error != nil {
                        print("user account doesnt exist")
                    } else {
                        print("You're logged in Fam")
                    }
    })
}

试试这个：

override func shouldPerformSegueWithIdentifier(identifier: String, sender: AnyObject?) -> Bool {
    if password incorrect {
        return false
    }else {
        return true
    }
}

或在成功验证后执行序列：

func userLogin (user: String!, pass: String!){
ref.authUser(user, password: pass,
             withCompletionBlock: { error, authData in
                if error != nil {
                    print("user account doesnt exist")
                } else {
                    print("You're logged in Fam")
                    performSegueWithIdentifier("Your identifier", sender: AnyObject?)
                }
})

}试试这个：

override func shouldPerformSegueWithIdentifier(identifier: String, sender: AnyObject?) -> Bool {
    if password incorrect {
        return false
    }else {
        return true
    }
}

或在成功验证后执行序列：

func userLogin (user: String!, pass: String!){
ref.authUser(user, password: pass,
             withCompletionBlock: { error, authData in
                if error != nil {
                    print("user account doesnt exist")
                } else {
                    print("You're logged in Fam")
                    performSegueWithIdentifier("Your identifier", sender: AnyObject?)
                }
})

}