Logic errors with password authentication code - ios

Question

My code is as follows:
#IBAction func clicked(_ sender: Any) {
let ref = Database.database().reference()
let pass = password.text
var firpass = ""
var bool = false;
ref.child(name.text as! String).child("password").observeSingleEvent(of: .value, with: { dataSnapshot in
firpass = dataSnapshot.value as? String ?? ""
if firpass == pass {
bool = true
}
if bool {
self.sendname = self.name.text!
let vc = DatabaseTableViewController(nibName: "DatabaseTableViewController", bundle: nil)
vc.finalName = self.sendname
self.navigationController?.pushViewController(vc, animated: true)
self.performSegue(withIdentifier: "username", sender: self)
} else {
let alert = UIAlertController(title: "Error", message: "Incorrect username or password", preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.default, handler: nil))
self.present(alert, animated: true, completion: nil)
self.performSegue(withIdentifier: "failed", sender: self)
}
})
}
override func shouldPerformSegue(withIdentifier identifier: String?, sender: Any?) -> Bool {
if let ident = identifier {
if ident == "failed" {
return false
}
}
return true
}
When I give the right username and password, I go to the next page, but I get this error:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Receiver (<OCRApp.ViewController: 0x105e00f60>) has no segue with identifier 'failed''
*** First throw call stack:
(0x1877aaa48 0x1874d1fa4 0x18b206010 0x104a5b58c 0x104a5ba20 0x104aaa19c 0x104aaa598 0x104a8bb40 0x105cd97fc 0x105cdabd8 0x105ce8c34 0x1877285e4 0x1877235d8 0x187722adc 0x1916a8328 0x18b81dae0 0x104a6cdb0 0x1875ac360)
libc++abi.dylib: terminating with uncaught exception of type NSException
When I give the wrong username/password, I still went to the next page, and I got the above error but with identifier failed instead; when I took out the line self.performSegue(withIdentifier: "failed", sender: self), I still went to the next page and got the message:
Warning: Attempt to present <UIAlertController: 0x102978a00> on <OCRApp.ViewController: 0x10170a650> which is already presenting <OCRApp.DatabaseTableViewController: 0x10206beb0>
What I want is to progress to the next page without errors if you put the correct authentication, and to get just the alert and stay on current page if you give incorrect authentication. How do I do this?

Answer 1

Either use push or performSegue, you cant use both at same time. that will push your view controller twice. I have updated the code below.
#IBAction func clicked(_ sender: Any) {
let ref = Database.database().reference()
let pass = password.text
var firpass = ""
var bool = false;
ref.child(name.text as! String).child("password").observeSingleEvent(of: .value, with: { dataSnapshot in
firpass = dataSnapshot.value as? String ?? ""
if firpass == pass {
bool = true
}
if bool {
self.sendname = self.name.text!
let vc = DatabaseTableViewController(nibName: "DatabaseTableViewController", bundle: nil)
vc.finalName = self.sendname
self.navigationController?.pushViewController(vc, animated: true) // either use push or performSegue, you cant use both.
// self.performSegue(withIdentifier: "username", sender: self)
} else {
let alert = UIAlertController(title: "Error", message: "Incorrect username or password", preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.default, handler: nil))
self.present(alert, animated: true, completion: nil) // if there is an error, you do not need to performSegue.
// self.performSegue(withIdentifier: "failed", sender: self)
}
})
}

Answer 2

We do not have information about your segues, I suggest you instantiate your next ViewController. You can use something like this:
let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "NextViewController") as? NextViewController
present(vc, animated: true, completion: nil)