Swift（Xcode）：如何获取系统访问码拦截应用控制器？

Hey there! I’ve built similar functionality before, so let’s break down exactly how to make this work in your app. The core goal is twofold: shut down all custom access code creation flows and replace them with Apple’s native LocalAuthentication framework to leverage the system’s passcode/TouchID/FaceID.

Step 1: Intercept & Disable Custom Access Code Entries #

First, you need to cut off every path that lets users create a custom access code:

• If you have a dedicated CreateAccessCodeViewController, either remove all logic that presents/pushes this VC, or override its viewDidLoad to immediately trigger system authentication instead of showing the custom UI.
• For any buttons/table cells that previously launched custom access code setup, rewire their actions to call your system authentication method (we’ll write that next) and disable/hide the old custom options.

Example of updating a button action:

// Old code that opened custom access code VC
// @IBAction func createCustomAccessCodeTapped(_ sender: UIButton) {
//     present(CreateAccessCodeVC(), animated: true)
// }

// New code that triggers system authentication
@IBAction func verifyWithSystemPasscodeTapped(_ sender: UIButton) {
    authenticateWithSystemPasscode()
}

If you have a settings screen with a "Create Access Code" option, modify it to reflect the system-based flow:

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "AccessCodeCell", for: indexPath)
    if indexPath.row == 0 { // Old custom access code cell
        cell.textLabel?.text = "System Passcode Verification"
        cell.detailTextLabel?.text = "Uses your device's built-in passcode"
        cell.isUserInteractionEnabled = false // Disable tapping to old flow
    }
    return cell
}

Step 2: Implement System Authentication with LocalAuthentication #

Apple’s LocalAuthentication framework handles all native passcode/TouchID/FaceID validation automatically. It will fall back to the system passcode if biometrics aren’t available or the user chooses to use their passcode instead.

First, import the framework:

import LocalAuthentication

Then write a reusable authentication function:

func authenticateWithSystemPasscode() {
    let context = LAContext()
    var authError: NSError?
    
    // Check if the device supports system-level authentication
    guard context.canEvaluatePolicy(.deviceOwnerAuthentication, error: &authError) else {
        // Device doesn't have a passcode/biometrics set up
        showSetupPasscodePrompt()
        return
    }
    
    // Trigger the system authentication prompt
    let reason = "Verify your device passcode to continue"
    context.evaluatePolicy(.deviceOwnerAuthentication, localizedReason: reason) { [weak self] success, error in
        // Always run UI updates on the main thread
        DispatchQueue.main.async {
            guard let self = self else { return }
            
            if success {
                // Authentication passed — proceed with your app's logic
                print("System authentication successful!")
                self.navigateToMainApp() // Example: Unlock main content
            } else {
                // Handle authentication failure
                if let error = error as? LAError {
                    switch error.code {
                    case .userCancel:
                        print("User canceled authentication")
                    case .userFallback:
                        print("User chose to enter passcode")
                    default:
                        print("Authentication failed: \(error.localizedDescription)")
                    }
                }
            }
        }
    }
}

Step 3: Handle Cases Where No System Passcode Is Set #

If the user hasn’t set up a device passcode or biometrics, guide them to enable it in system settings:

func showSetupPasscodePrompt() {
    let alert = UIAlertController(
        title: "No Device Passcode Found",
        message: "Please set up a passcode in your device settings to use this feature.",
        preferredStyle: .alert
    )
    
    alert.addAction(UIAlertAction(title: "Go to Settings", style: .default) { _ in
        if let settingsURL = URL(string: UIApplication.openSettingsURLString) {
            UIApplication.shared.open(settingsURL)
        }
    })
    
    alert.addAction(UIAlertAction(title: "Cancel", style: .cancel))
    present(alert, animated: true)
}

Important Notes #

• Info.plist Requirements: If your app supports FaceID, add the NSFaceIDUsageDescription key to your Info.plist with a clear reason (e.g., "Use Face ID to verify your identity and access the app"). Without this, your app will crash when attempting FaceID authentication.
• Clean Up Old Code: Remove any logic that stored custom access codes (e.g., Keychain entries, UserDefaults) to avoid conflicts or unused code.
• Test Edge Cases: Verify behavior on devices with TouchID, FaceID, only passcode, and no authentication set up to ensure full coverage.

内容的提问来源于stack exchange，提问作者Bartłomiej Janczak