Swift LocalAuthentication issue with faceID resetting my state vars. Stopped working with iOS 17

Question

I'm trying to change a state bool var with faceID.

My Test Code.

import SwiftUI
import LocalAuthentication

struct PasswordEditTest: View {
    
    @State private var showPassword: Bool = false
  
    var body: some View {
        
        HStack {
            Section(header: Text("Password:").foregroundColor(Color.theme.red)
            ) {
                
                if  showPassword {
                    Text("UNLOCKED")
                }
                else {
                    Text("LOCKED")
                }
            }
            
            Spacer()
             
             Image(systemName: showPassword ? "lock.open" : "lock")
                 .resizable()
                 .scaledToFill()
                 .frame(width: showPassword ? 30 : 30, height: showPassword ? 39 : 39)
                 .padding()
                 .onTapGesture {
                     
                     let context = LAContext()
                     var error: NSError?
                    
                     if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
                         let reason = "We need to unlock your password"
                         
                         context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) { success, authenticationError in
                                 if success {
                                     
                                     print("SUCCESS")
                                     showPassword=true
                                    
                                 } else {
                                     
                                     print("FAIL")
                                     
                                     showPassword=false
                                    
                                 }
                             
                         }
                     } else {
                        //NO FACEID/Biometrics
                         
                     }
                     
                     
                 }
            
        }
        
    }
    
}

If I change the showPassword to TRUE on the tap gesture, once the faceid success fires it will change the var back to false, So strange. It was working fine on iOS16

.onTapGesture {
                     showPassword=true //ADD THIS

                     let context = LAContext()
                     var error: NSError?
                    
                     if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
                         let reason = "We need to unlock your password"
                         
                         context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) { success, authenticationError in
                                 if success {
                                     
                                  // the showPassword will change back to false. 

                                     print("SUCCESS")
                                     showPassword=true.  // This will not change it to true Crazy!
                                    
                                 } else {
                                     
                                     print("FAIL")
                                     
                                     showPassword=false
                                    
                                 }
                             
                         }
                     } else {
                        //NO FACEID/Biometrics
                         
                     }

Your code works for me as-is on iOS 17.2.1. I do note that the documentation for evaluatePolicy states that the closure is executed in an unspecified threading context so you should dispatch your state update onto the main queue. — Paulw11
– Paulw11, Commented Jan 21, 2024 at 22:50

lorem ipsum · Accepted Answer · 2024-01-22 01:14:01Z

0

You can switch to the async/await version, it will ensure that the result is received in the MainActor

import SwiftUI
import LocalAuthentication

struct PasswordResetTest: View {
    @State private var showPassword: Bool = false
    @State private var isEvaluatingPolicy: Bool = false
    var body: some View {
        
        HStack {
            Section(header: Text("Password:").foregroundColor(Color.red)
            ) {
                
                if  showPassword {
                    Text("UNLOCKED")
                }
                else {
                    Text("LOCKED")
                }
            }
            
            Spacer()
            
            Image(systemName: showPassword ? "lock.open" : "lock")
                .resizable()
                .scaledToFill()
                .frame(width: showPassword ? 30 : 30, height: showPassword ? 39 : 39)
                .padding()
                .onTapGesture {
                    //Start evaluating policy
                    isEvaluatingPolicy.toggle()
                }
                .task(id: isEvaluatingPolicy) {
                    guard isEvaluatingPolicy else {return}
                    let context = LAContext()
                    let policy: LAPolicy = .deviceOwnerAuthenticationWithBiometrics
                    do {
                        try context
                            .canEvaluatePolicy(policy)
                        showPassword = try await context
                            .evaluatePolicy(policy, localizedReason: "We need to unlock your password")
                        print("Was successful = \(showPassword.description)")
                    } catch {
                        print(error) //Should display error to user.
                    }
                    isEvaluatingPolicy = false //Done evaluating policy
                }
        }
    }
}

The referenced canEvaluatePolicy is a simple conversion of the existing methodology.

extension LAContext {
    /// Assesses whether authentication can proceed for a given policy.
    /// - Parameter policy: The policy to evaluate. For possible values,
    func canEvaluatePolicy(_ policy: LAPolicy) throws {
        var error: NSError?
        if self
            .canEvaluatePolicy(policy, error: &error) {
            //Done
        } else if let error {
            throw error
        } else {
            throw LocalError.cannotBeEvaluated(policy)
        }
    }
    
    private enum LocalError: LocalizedError {
        case cannotBeEvaluated(LAPolicy)
        var errorDescription: String?{
            switch self {
            case .cannotBeEvaluated(let lAPolicy):
                return "Policy cannot be evaluated."
            }
        }
    }
}

answered Jan 22, 2024 at 1:14

lorem ipsum

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4 Comments

neogaz Over a year ago

Thank you for this, but it still fails. When the .deviceOwnerAuthenticationWithBiometrics is processed it will reset the showPassword back to the default value. I don't get it. My target ios is 17.1. (for test) If I set showPassword=true and then process .canEvaluatePolicy(policy) it will instantly change the showPassword=false. Before I match the faceID. So strange!

lorem ipsum Over a year ago

@neogaz there is something else going on then that isn’t depicted in your sample. Something is changing the identity of the view.

neogaz Over a year ago

You are correct. I went one level up in my tabview and it works, so odd ios 17 update killed something. It's been working great! Thanks for your help!!

lorem ipsum Over a year ago

@neogaz glad to help. Do you mind clicking on the green checkmark to accept the answer?

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