在初始化之前由闭包捕获的变量'isVericated' - Swift

Question

我试图从名为identityVerification 的函数中返回一个名为isVerificated 的布尔变量，因此我可以在tableView 函数中使用它。函数identityVerification通过Face ID或Touch ID启动身份验证，返回变量isVerificated，告知验证是否成功。

换句话说： 我的目标是当你点击 TableView 中的一个单元格时，它应该首先使用 Face ID 或 Touch ID 开始身份验证。然后身份验证成功后，会打开一个新的ViewController。如果身份验证失败，应用会显示一个 AlertController 并显示消息：“Authentication failed”，并且不会打开新的 ViewController。

问题： 当我运行应用程序时出现两个错误：

1. (!) 变量“isVericated”在被初始化之前被闭包捕获
2. (!) 变量“isVericated”在初始化之前使用

代码如下：

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        let IDisVarificated = identityVerification()    //here the "identityVerification" function is started
        if IDisVarificated == true {
            if let vc = storyboard?.instantiateViewController(withIdentifier: "detail") as? PasswordTVcontroller {
                navigationController?.pushViewController(vc, animated: true)
            }
        } else {return}
    }
    
    
    func identityVerification() -> Bool {
        var isVerificated: Bool
        let context = LAContext()
        var error: NSError?

        if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {   //HERE IS ERROR NUMBER 1
            let reason = "Identify yourself!"

            context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) {
                [weak self] success, authenticationError in

                DispatchQueue.main.async {
                    if success {
                        isVerificated = true    //verification was successfull
                    } else {
                        let ac = UIAlertController(title: "Authentication failed", message: "You could not be verified; please try again.", preferredStyle: .alert)
                        ac.addAction(UIAlertAction(title: "OK", style: .default))
                        self?.present(ac, animated: true)
                        isVerificated = false     //verification failed
                    }
                }
            }
        } else {
            let ac = UIAlertController(title: "Biometry unavailable", message: "Your device is not configured for biometric authentication.", preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "OK", style: .default))
            self.present(ac, animated: true)
            isVerificated = false      //verification failed
        }
        
        return isVerificated      //returning a variable with boolean value that tells if verification was successfull or not, HERE IS ERROR NUMBER 2
    }

感谢您的帮助！

Answer 1

这类问题总是出现在不熟悉异步函数的人身上。

您不能编写一个从LAContext 函数evaluatePolicy(_:localizedReason:reply:) 返回结果的函数。期间。

那个函数是异步的。这意味着它不会返回结果。它立即返回，然后在后台执行您要求它执行的工作。工作完成后，它会调用 reply 闭包。

您的代码尝试在闭包内设置一个局部变量isVerificated。那是行不通的。当闭包运行时，你的函数已经返回了。

您需要重写您的函数 identityVerification 以采用闭包而不是返回函数。重构后的函数可能如下所示：

func identityVerification(completion: (Bool) -> Void) {
        let context = LAContext()
        var error: NSError?

        if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {   //HERE IS ERROR NUMBER 1
            let reason = "Identify yourself!"

            context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) {
                [weak self] success, authenticationError in

                DispatchQueue.main.async {
                    if success {
                        completion(true)
                    } else {
                        let ac = UIAlertController(title: "Authentication failed", message: "You could not be verified; please try again.", preferredStyle: .alert)
                        ac.addAction(UIAlertAction(title: "OK", style: .default))
                        self?.present(ac, animated: true)
                        completion(false)
                    }
                }
            }
        } else {
            let ac = UIAlertController(title: "Biometry unavailable", message: "Your device is not configured for biometric authentication.", preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "OK", style: .default))
            self.present(ac, animated: true)
            completion(false)
        }
}