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iOS系统的指纹识别功能最低支持的机型为iPhone 5s，最低支持系统为iOS 8，虽然安装iOS 7系统的5s机型可以使用系统提供的指纹解锁功能，但由于API并未开放，所以理论上第三方软件不可使用。
LocalAuthentication.framework
#import
做iOS 8以下版本适配时，务必进行API验证，避免调用相关API引起崩溃。
LAContext 指纹验证操作对象
- (void)authenticateUser{ //初始化上下文对象 LAContext* context = [[LAContext alloc] init]; //错误对象 NSError* error = nil; NSString* result = @"Authentication is needed to access your notes."; //首先使用canEvaluatePolicy 判断设备支持状态 if ([context canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&error]) { //支持指纹验证 [context evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics localizedReason:result reply:^(BOOL success, NSError *error) { if (success) { //验证成功，主线程处理UI } else { NSLog(@"%@",error.localizedDescription); switch (error.code) { case LAErrorSystemCancel: { NSLog(@"Authentication was cancelled by the system"); //切换到其他APP，系统取消验证Touch ID break; } case LAErrorUserCancel: { NSLog(@"Authentication was cancelled by the user"); //用户取消验证Touch ID break; } case LAErrorUserFallback: { NSLog(@"User selected to enter custom password"); [[NSOperationQueue mainQueue] addOperationWithBlock:^{ //用户选择输入密码，切换主线程处理 }]; break; } default: { [[NSOperationQueue mainQueue] addOperationWithBlock:^{ //其他情况，切换主线程处理 }]; break; } } } }]; } else { //不支持指纹识别，LOG出错误详情 switch (error.code) { case LAErrorTouchIDNotEnrolled: { NSLog(@"TouchID is not enrolled"); break; } case LAErrorPasscodeNotSet: { NSLog(@"A passcode has not been set"); break; } default: { NSLog(@"TouchID not available"); break; } } NSLog(@"%@",error.localizedDescription); }} typedef NS_ENUM(NSInteger, LAError){ //授权失败 LAErrorAuthenticationFailed = kLAErrorAuthenticationFailed, //用户取消Touch ID授权 LAErrorUserCancel = kLAErrorUserCancel, //用户选择输入密码 LAErrorUserFallback = kLAErrorUserFallback, //系统取消授权(例如其他APP切入) LAErrorSystemCancel = kLAErrorSystemCancel, //系统未设置密码 LAErrorPasscodeNotSet = kLAErrorPasscodeNotSet, //设备Touch ID不可用，例如未打开 LAErrorTouchIDNotAvailable = kLAErrorTouchIDNotAvailable, //设备Touch ID不可用，用户未录入 LAErrorTouchIDNotEnrolled = kLAErrorTouchIDNotEnrolled,} NS_ENUM_AVAILABLE(10_10, 8_0); 首先判断系统版本，iOS 8及以上版本执行-(void)authenticateUser方法，方法自动判断设备是否支持和开启Touch ID。
感谢指出iOS 9加入了三种新的错误类型。
/// 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. LAErrorTouchIDLockout NS_ENUM_AVAILABLE(10_11, 9_0) = kLAErrorTouchIDLockout, /// Authentication was canceled by application (e.g. invalidate was called while /// authentication was in progress). LAErrorAppCancel NS_ENUM_AVAILABLE(10_11, 9_0) = kLAErrorAppCancel, /// LAContext passed to this call has been previously invalidated. LAErrorInvalidContext NS_ENUM_AVAILABLE(10_11, 9_0) = kLAErrorInvalidContext
其中，LAErrorTouchIDLockout是在8.0中也会出现的情况，但并未归为单独的错误类型，这个错误出现，源自用户多次连续使用Touch ID失败，Touch ID被锁，需要用户输入密码解锁，这个错误的交互LocalAuthentication.framework已经封装好了，不需要开发者关心。
LAErrorAppCancel和LAErrorSystemCancel相似，都是当前软件被挂起取消了授权，但是前者是用户不能控制的挂起，例如突然来了电话，电话应用进入前台，APP被挂起。后者是用户自己切到了别的应用，例如按home键挂起。
LAErrorInvalidContext很好理解，就是授权过程中,LAContext对象被释放掉了，造成的授权失败。
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