某些 iPad 设备 return 生物识别无法使用此代码，为什么？

Question

我在理解 return 值时遇到了一些问题，我在一个仅包含以下代码的新项目中得到的值。

- (void)viewDidLoad {
    [super viewDidLoad];

    LAContext*   touchContext          = [LAContext new];
    NSError*     policyEvaluationError = nil;

    [touchContext canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics
                                            error:&policyEvaluationError];

    NSLog(@"\n\n %@", policyEvaluationError);
}

这些是 iPad 模拟器的结果，iOS 10.3.1 - 11.3。

iPad (5th Generation) - "Biometry is not available on this device."

iPad Air - "Biometry is not available on this device."

iPad Air 2 - “No identities are enrolled."

iPad Pro (9.7-inch) - "Biometry is not available on this device."

iPad Pro (12.9-inch) (2nd generation) - "Biometry is not available on this device."

“生物识别在此设备上不可用”的这些结果。这些设备是否注册时都会发生。

还测试了所有 iPhone 设备类型 return“未注册任何身份。”像 iPad Air 2，我希望他们没有注册但拥有 touchID 硬件。注册的时候，根本就没有错误。

在一些实际的 iPad 设备上，结果似乎也有所不同，但方式不同。如果不存储指纹，某些设备 return“此设备不支持生物识别。”而其他人只是 return enrolled/nil。存储指纹后，它们的行为似乎都符合我的预期。

据我所知，我们已经在生产中使用这段代码很长一段时间了，没有收到与此主题相关的投诉，但我们最近才在 development/QA 中注意到它。

此代码是否在所有设备上都不可靠，是否可能发生了某些变化，或者我在这里做错了什么？

Answer 1

这是 Apple 框架中的错误，我已将其提交给 rdar://problem/46148637。如果你很好奇，这里是该报告的全文：

iPad Pro (12.9-inch) (2nd generation) simulator thinks it doesn't have Touch ID

Summary:
LAContext().canEvaluatePolicy(_:error:) with the policy LAPolicy.deviceOwnerAuthenticationWithBiometrics fails with LAError.Code. biometryNotAvailable on the iPad Pro (12.9-inch) (2nd generation) simulator. A bit of digging suggests that:

• LAContext().canEvaluatePolicy(_:error:), from LocalAuthentication.framework, ends up communicating with coreauthd to evaluate the policy.
• The specific error is generated in -[BiometryHelper deviceHasBiometryWithError:] in DaemonUtils.framework, which is loaded into coreauthd.
• -[BiometryHelper deviceHasBiometryWithError:] returns this error when -BiometryHelper._device is nil.
• BiometryHelper._device is the first object grabbed from +[BKDeviceManager availableDevices], in BiometricKit.framework.
• +[BKDeviceManager availableDevices] *should* create a Touch ID device descriptor if it finds that the device supports Touch ID, which it checks by calling MGGetBoolAnswer(@"touch-id").
• MGGetBoolAnswer(@"touch-id") returns NO (!)
• The device believes it does not have a Touch ID sensor.
• LAContext().canEvaluatePolicy(_:error:) returns false because it believes the device cannot evaluate this policy.

Steps to Reproduce:
1. Try to evaluate a biometric policy on the  iPad Pro (12.9-inch) (2nd generation) simulator.

Expected Results:
I either receive a success, or something about being unenrolled.

Actual Results:
I'm told that this iPad doesn't have a Touch ID sensor, when clearly should have one.

Version/Build:
Xcode Version 10.1 (10B61)

Configuration:
Xcode Version 10.1 (10B61)/macOS Mojave 10.14.2 Beta (18C48a)

某些 iPad 设备 return 生物识别无法使用此代码，为什么？

Some iPad devices return biometrics not available with this code, why?

biometrics

ipad

ios

ios-simulator

touch-id