Touch ID 指紋識別首次應(yīng)用是在2013年9月發(fā)布的iPhone 5s 上仑濒。在今天，指紋識別已經(jīng)是所有智能手機(jī)必不可少的一部分。它不僅能保證手機(jī)中信息的安全拐云，管理自己的隱私婿着，還能夠快捷快速的進(jìn)行密碼輸入等操作授瘦。在保證安全的同時也提高了使用的效率。
雖說Touch ID 誕生在iPhone 5s竟宋，但是在iOS 8 中才正式開放API提完。而且隨著手機(jī)硬件的升級，Touch ID 的識別效率大大提高丘侠，這使得越來越多的App加入了指紋解鎖的功能徒欣。
LAContext提供了關(guān)于指紋識別的接口。這里有幾個主要的方法和屬性：

canEvaluatePolicy 方法來判斷設(shè)備是否支持指紋識別蜗字。
evaluatePolicy 方法來進(jìn)行指紋識別打肝。
invalidate 方法主動讓指紋識別上下文失效官研。 （iOS 9+）
localizedFallbackTitle 屬性 設(shè)置驗(yàn)證第一次失敗后顯示按鈕的標(biāo)題。
localizedCancelTitle 屬性設(shè)置取消驗(yàn)證按鈕的標(biāo)題闯睹。

使用

在iOS 中加入Touch ID 指紋非常簡單戏羽，只需要幾句代碼就能搞定，

首先需要引入LocalAuthentication

import LocalAuthentication

初始化驗(yàn)證上下文

let context = LAContext()
// 在第一次驗(yàn)證失敗之后楼吃，可以提供別的方式的入口
context.localizedFallbackTitle = "使用密碼登錄"

進(jìn)行驗(yàn)證始花，蘋果提供了一個LAError 來捕捉Touch ID 驗(yàn)證過程中可能會出現(xiàn)的錯誤，我們可以針對錯誤類型來進(jìn)行預(yù)期處理孩锡。

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("驗(yàn)證成功")
        } else {
            if let error = error as? LAError {
                switch error.code {
                /// Authentication was not successful, because user failed to provide valid credentials.
                case .authenticationFailed:
                    print("連續(xù)3次驗(yàn)證失敗")
                /// Authentication was canceled by user (e.g. tapped Cancel button).
                case .userCancel:
                    print("用戶取消驗(yàn)證")
                /// Authentication was canceled, because the user tapped the fallback button (Enter Password).
                case .userFallback:
                    OperationQueue.main.addOperation {
                    print("用戶選擇輸入密碼酷宵，切換主線程處理")
                    }
                /// Authentication was canceled by system (e.g. another application went to foreground).
                case .systemCancel:
                    print("系統(tǒng)取消")
                /// Authentication could not start, because passcode is not set on the device.
                case .passcodeNotSet:
                    print("未設(shè)置密碼")
                /// Authentication could not start, because Touch ID is not available on the device.
                case .touchIDNotAvailable:
                    print("硬件問題導(dǎo)致不可用")
                /// Authentication could not start, because Touch ID has no enrolled fingers.
                case .touchIDNotEnrolled:
                    print("手指未登記")
                /// 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鎖定")
                /// 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("無效的驗(yàn)證上下文")
                }
            }
        }
    })
}