How to use passcode lock scene in my app?

Question

Actually, I building an app which contains local authentication.

My code so far:

func authenticateUser() {
        let authenticationContext = LAContext()
        var error: NSError?
        let reasonString = "Touch the Touch ID sensor to unlock."

        // Check if the device can evaluate the policy.
        if authenticationContext.canEvaluatePolicy(LAPolicy.deviceOwnerAuthenticationWithBiometrics, error: &error) {

            authenticationContext.evaluatePolicy( .deviceOwnerAuthenticationWithBiometrics, localizedReason: reasonString, reply: { (success, evalPolicyError) in

                if success {
                    print("success")
                } else {
                    if let evaluateError = error as NSError? {
                        // enter password using system UI 
                    }

                }
            })

        } else {
            print("toch id not available")
           // enter password using system UI
        }
    }

My problem is I want to use the passcode lock scene when the app doesn't has touch ID or invalid finger print.

Like below Image:

How can I do it?

Answer 1

You should use .deviceOwnerAuthentication instead of .deviceOwnerAuthenticationWithBiometrics to evaluate policy. With this parameter the system uses biometric authentication if available else it presents passcode screen. And if the biometric authentication is available but fails, a fallback button redirect to the passcode screen. See documentation :

If Touch ID or Face ID is available, enrolled, and not disabled, the user is asked for that first. Otherwise, they are asked to enter the device passcode.

Tapping the fallback button switches the authentication method to ask the user for the device passcode.

So your code will be:

func authenticateUser() {
        let authenticationContext = LAContext()
        var error: NSError?
        let reasonString = "Touch the Touch ID sensor to unlock."

        // Check if the device can evaluate the policy.
        if authenticationContext.canEvaluatePolicy(LAPolicy.deviceOwnerAuthentication, error: &error) {

            authenticationContext.evaluatePolicy( .deviceOwnerAuthentication, localizedReason: reasonString, reply: { (success, evalPolicyError) in

                if success {
                    print("success")
                } else {
                    // Handle evaluation failure or cancel
                }
            })

        } else {
            print("passcode not set")
        }
    }