Touch ID 指纹识别首次应用是在2013年9月发布的iPhone 5s 上。在今天，指纹识别已经是所有智能手机必不可少的一部分。它不仅能保证手机中信息的安全，管理自己的隐私，还能够快捷快速的进行密码输入等操作。在保证安全的同时也提高了使用的效率。
虽说Touch ID 诞生在iPhone 5s，但是在iOS 8 中才正式开放API。而且随着手机硬件的升级，Touch ID 的识别效率大大提高，这使得越来越多的App加入了指纹解锁的功能。
LAContext提供了关于指纹识别的接口。这里有几个主要的方法和属性：
canEvaluatePolicy 方法来判断设备是否支持指纹识别。
evaluatePolicy 方法来进行指纹识别。
invalidate 方法主动让指纹识别上下文失效。 （iOS 9+）
localizedFallbackTitle 属性 设置验证第一次失败后显示按钮的标题。
localizedCancelTitle 属性设置取消验证按钮的标题。
使用
在iOS 中加入Touch ID 指纹非常简单，只需要几句代码就能搞定，
首先需要引入LocalAuthentication
import LocalAuthentication
初始化验证上下文
let context = LAContext()
// 在第一次验证失败之后，可以提供别的方式的入口
context.localizedFallbackTitle = "使用密码登录"
进行验证，苹果提供了一个LAError 来捕捉Touch ID 验证过程中可能会出现的错误，我们可以针对错误类型来进行预期处理。
var contentError: NSError?
if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &contentError) {
context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: "按下你的手指", reply: { (success, error) in
if success {
print("验证成功")
} else {
if let error = error as? LAError {
switch error.code {
/// Authentication was not successful, because user failed to provide valid credentials.
case .authenticationFailed:
print("连续3次验证失败")
/// Authentication was canceled by user (e.g. tapped Cancel button).
case .userCancel:
print("用户取消验证")
/// Authentication was canceled, because the user tapped the fallback button (Enter Password).
case .userFallback:
OperationQueue.main.addOperation {
print("用户选择输入密码，切换主线程处理")
}
/// Authentication was canceled by system (e.g. another application went to foreground).
case .systemCancel:
print("系统取消")
/// Authentication could not start, because passcode is not set on the device.
case .passcodeNotSet:
print("未设置密码")
/// Authentication could not start, because Touch ID is not available on the device.
case .touchIDNotAvailable:
print("硬件问题导致不可用")
/// Authentication could not start, because Touch ID has no enrolled fingers.
case .touchIDNotEnrolled:
print("手指未登记")
/// Authentication was not successful, because there were too many failed Touch ID attempts and
/// Touch ID is now locked. Passcode is required to unlock Touch ID, e.g. evaluating
/// LAPolicyDeviceOwnerAuthenticationWithBiometrics will ask for passcode as a prerequisite.
/// iOS 9+
case .touchIDLockout:
print("TouchID锁定")
/// Authentication was canceled by application (e.g. invalidate was called while
/// authentication was in progress).
/// iOS 9+
case .appCancel:
print("程序退出")
/// LAContext passed to this call has been previously invalidated.
/// iOS 9+
case .invalidContext:
print("无效的验证上下文")
}
}
}
})
}
