Biometric Authentication evaluation with swiftUI - swift

Question

I've been able to get a rudimentary version of Face / Touch ID working inside my app. However, I want to add better fallbacks and error handling.
So I've been researching how to do it. There are fantastic resources like this:
Face ID evaluation process not working properly
However, I can't find anything that works inside a SwiftUI view. At the moment my project won't run with:
'unowned' may only be applied to class and class-bound protocol types, not 'AuthenticateView'
and
Value of type 'AuthenticateView' has no member 'present'
any help would be much appreciated. Thank you!
Here's my code inside AuthenticateView.swift
func Authenticate(completion: #escaping ((Bool) -> ())){
//Create a context
let authenticationContext = LAContext()
var error:NSError?
//Check if device have Biometric sensor
let isValidSensor : Bool = authenticationContext.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error)
if isValidSensor {
//Device have BiometricSensor
//It Supports TouchID
authenticationContext.evaluatePolicy(
.deviceOwnerAuthenticationWithBiometrics,
localizedReason: "Touch / Face ID authentication",
reply: { [unowned self] (success, error) -> Void in
if(success) {
// Touch / Face ID recognized success here
completion(true)
} else {
//If not recognized then
if let error = error {
let strMessage = self.errorMessage(errorCode: error._code)
if strMessage != ""{
self.showAlertWithTitle(title: "Error", message: strMessage)
}
}
completion(false)
}
})
} else {
let strMessage = self.errorMessage(errorCode: (error?._code)!)
if strMessage != ""{
self.showAlertWithTitle(title: "Error", message: strMessage)
}
}
}
func errorMessage(errorCode:Int) -> String{
var strMessage = ""
switch errorCode {
case LAError.Code.authenticationFailed.rawValue:
strMessage = "Authentication Failed"
case LAError.Code.userCancel.rawValue:
strMessage = "User Cancel"
case LAError.Code.systemCancel.rawValue:
strMessage = "System Cancel"
case LAError.Code.passcodeNotSet.rawValue:
strMessage = "Please goto the Settings & Turn On Passcode"
case LAError.Code.touchIDNotAvailable.rawValue:
strMessage = "TouchI or FaceID DNot Available"
case LAError.Code.touchIDNotEnrolled.rawValue:
strMessage = "TouchID or FaceID Not Enrolled"
case LAError.Code.touchIDLockout.rawValue:
strMessage = "TouchID or FaceID Lockout Please goto the Settings & Turn On Passcode"
case LAError.Code.appCancel.rawValue:
strMessage = "App Cancel"
case LAError.Code.invalidContext.rawValue:
strMessage = "Invalid Context"
default:
strMessage = ""
}
return strMessage
}
func showAlertWithTitle( title:String, message:String ) {
let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
let actionOk = UIAlertAction(title: "OK", style: .default, handler: nil)
alert.addAction(actionOk)
self.present(alert, animated: true, completion: nil)
}

Answer 1

Explanation:
'unowned' may only be applied to class and class-bound protocol types, not 'AuthenticateView'
First of all, you have AuthenticateView which is a struct. You can't do it class because whole Apple's SwiftUI idea is about structures. And because Struct is value type and not a Reference type, so no pointer as such. So you may not include code parts containing unowned self and weak self modifiers into struct AuthenticateView: View {}
Value of type 'AuthenticateView' has no member 'present'
present is a UIViewController's method. Here in SwiftUI you have no access to it. The alerts are being presented using the next style:
struct ContentView: View {
#State private var show = false
var body: some View {
Button(action: { self.show = true }) { Text("Click") }
.alert(isPresented: $showingAlert) {
Alert(title: Text("Title"),
message: Text("Message"),
dismissButton: .default(Text("Close")))
}
}
}
Solution:
For your case, I would create a class Handler subclass of ObservableObject for your logic and use the power of #ObservedObject, #Published and #State.
Rough example for understanding the concept:
import SwiftUI
struct ContentView: View {
#ObservedObject var handler = Handler()
var body: some View {
Button(action: { self.handler.toggleShowAlert() }) { Text("Click") }
.alert(isPresented: $handler.shouldShowAlert) {
Alert(title: Text(handler.someTitle),
message: Text(handler.someMessage),
dismissButton: .default(Text("Close")))
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
class Handler: ObservableObject {
#Published var shouldShowAlert: Bool = false
#Published var someTitle = ""
#Published var someMessage = ""
func toggleShowAlert() {
shouldShowAlert.toggle()
someTitle = "ErrorTitle"
someMessage = "ErrorMessage"
}
}