公司的项目因为都涉及用户信息，因此都使用到了TouchID来身份识别，因此自己也是开始着手看了代码，了解了这个部分的知识
首先引入LocalAuthentication framework 框架，这个框架里面只有4个头文件。
LAContext.h(核心)
LAError.h
LAPublicDefines.h
LocalAuthentication.h
看一下LAContext.h的源码
//
// LAContext.h
// LocalAuthentication
//
// Copyright (c) 2014 Apple. All rights reserved.
//
#import <Foundation/Foundation.h>
#import <LocalAuthentication/LAPublicDefines.h>
NS_ASSUME_NONNULL_BEGIN
typedef NS_ENUM(NSInteger, LAPolicy)
{
/// Device owner was authenticated using a biometric method (Touch ID).
///
/// @discussion Touch ID authentication is required. If Touch ID is not available or not enrolled,
/// policy evaluation will fail. If Touch ID is locked out, passcode is required as
/// the first step to unlock the Touch ID.
///
/// Touch ID authentication dialog contains a cancel button with default title "Cancel"
/// which can be customized using localizedCancelTitle property and a fallback button with
/// default title "Enter Password" which can be customized using localizedFallbackTitle
/// property. Fallback button is initially hidden and shows up after first unsuccessful
/// Touch ID attempt. Tapping cancel button or fallback button causes evaluatePolicy call
/// to fail, returning a distinct error code.
///
/// Biometric authentication will get locked after 5 unsuccessful attempts. After that,
/// users have to unlock it by entering passcode.
指纹识别可以尝试5次，5次失败后，官方会自动让用户输入开机密码，这些都不需要开发者来操作
一般使用这个模式就可以了
LAPolicyDeviceOwnerAuthenticationWithBiometrics NS_ENUM_AVAILABLE(NA, 8_0) __WATCHOS_AVAILABLE(3.0) __TVOS_AVAILABLE(10.0) = kLAPolicyDeviceOwnerAuthenticationWithBiometrics,
/// Device owner was authenticated by Touch ID or device passcode.
///
/// @discussion Touch ID or passcode authentication is required. If Touch ID is available, enrolled and
/// not locked out, user is asked for it first, otherwise they are asked to enter device
/// passcode. If passcode is not enabled, policy evaluation will fail.
///
/// Touch ID authentication dialog behaves similarly as the one used by
/// LAPolicyDeviceOwnerAuthenticationWithBiometrics. However, instead of "Enter Password"
/// button there is "Enter Passcode" button which, when tapped, switches the authentication
/// method and allows users to enter device passcode.
///
/// Passcode authentication will get locked after 6 unsuccessful attempts with progressively
/// increased backoff delay.
//在六次识别失败后，会慢慢增加后面的延时
LAPolicyDeviceOwnerAuthentication NS_ENUM_AVAILABLE(10_11, 9_0) = kLAPolicyDeviceOwnerAuthentication
} NS_ENUM_AVAILABLE(10_10, 8_0) __WATCHOS_AVAILABLE(3.0) __TVOS_AVAILABLE(10.0);
/// The maximum value for LAContext touchIDAuthenticationAllowableReuseDuration property.
extern const NSTimeInterval LATouchIDAuthenticationMaximumAllowableReuseDuration NS_AVAILABLE(NA, 9_0) __WATCHOS_UNAVAILABLE __TVOS_UNAVAILABLE;
/// Class that represents an authentication context.
///
/// @discussion This context can be used for evaluating policies.
///
/// @see LAPolicy
NS_CLASS_AVAILABLE(10_10, 8_0) __WATCHOS_AVAILABLE(3.0) __TVOS_AVAILABLE(10.0)
@interface LAContext : NSObject
/// Determines if a particular policy can be evaluated.
///
/// @discussion Policies can have certain requirements which, when not satisfied, would always cause
/// the policy evaluation to fail. Examples can be a passcode set or a fingerprint
/// enrolled with Touch ID. This method allows easy checking for such conditions.
///
/// Applications should consume the returned value immediately and avoid relying on it
/// for an extensive period of time. At least, it is guaranteed to stay valid until the
/// application enters background.
///
/// @warning Do not call this method in the reply block of evaluatePolicy:reply: because it could
/// lead to a deadlock.
///
/// @param policy Policy for which the preflight check should be run.
///
/// @param error Optional output parameter which is set to nil if the policy can be evaluated, or it
/// contains error information if policy evaluation is not possible.
///
/// @return YES if the policy can be evaluated, NO otherwise.
//开发者主要调用这个函数，选择检验的方式，以及动态获取错误，根据错误的类型来做出不同状态的调整，
一般来说，判断有TouchID的话，接下来就会调用指纹检验了，是下面的函数
- (BOOL)canEvaluatePolicy:(LAPolicy)policy error:(NSError * __autoreleasing *)error __attribute__((swift_error(none)));
/// Evaluates the specified policy.
///
/// @discussion Policy evaluation may involve prompting user for various kinds of interaction
/// or authentication. Actual behavior is dependent on evaluated policy, device type,
/// and can be affected by installed configuration profiles.
///
/// Be sure to keep a strong reference to the context while the evaluation is in progress.
/// Otherwise, an evaluation would be canceled when the context is being deallocated.
///
/// The method does not block. Instead, the caller must provide a reply block to be
/// called asynchronously when evaluation finishes. The block is executed on a private
/// queue internal to the framework in an unspecified threading context. Other than that,
/// no guarantee is made about which queue, thread, or run-loop the block is executed on.
///
/// Implications of successful policy evaluation are policy specific. In general, this
/// operation is not idempotent. Policy evaluation may fail for various reasons, including
/// user cancel, system cancel and others, see LAError codes.
///
/// @param policy Policy to be evaluated.
///
/// @param reply Reply block that is executed when policy evaluation finishes.
/// success Reply parameter that is YES if the policy has been evaluated successfully or
/// NO if the evaluation failed.
/// error Reply parameter that is nil if the policy has been evaluated successfully, or it
/// contains error information about the evaluation failure.
///
/// @param localizedReason Application reason for authentication. This string must be provided in correct
/// localization and should be short and clear. It will be eventually displayed in
/// the authentication dialog. A name of the calling application will be already
/// displayed in title, so it should not be duplicated here.
///
/// @warning localizedReason parameter is mandatory and the call will throw NSInvalidArgumentException if
/// nil or empty string is specified.
///
/// @see LAError
///
/// Typical error codes returned by this call are:
/// @li LAErrorUserFallback if user tapped the fallback button
/// @li LAErrorUserCancel if user has tapped the Cancel button
/// @li LAErrorSystemCancel if some system event interrupted the evaluation (e.g. Home button pressed).
//核心函数，选择Policy，不同的policy显示不同界面效果，localizeReason为提示文字，reply为识别结果，开发者主要根据reply来处理结果
- (void)evaluatePolicy:(LAPolicy)policy
localizedReason:(NSString *)localizedReason
reply:(void(^)(BOOL success, NSError * __nullable error))reply;
/// Invalidates the context.
///
/// @discussion The context is invalidated automatically when it is (auto)released. This method
/// allows invalidating it manually while it is still in scope.
///
/// Invalidation terminates any existing policy evaluation and the respective call will
/// fail with LAErrorAppCancel. After the context has been invalidated, it can not be
/// used for policy evaluation and an attempt to do so will fail with LAErrorInvalidContext.
///
/// Invalidating a context that has been already invalidated has no effect.
- (void)invalidate NS_AVAILABLE(10_11, 9_0);
typedef NS_ENUM(NSInteger, LACredentialType)
{
/// Password provided by application
///
/// @discussion If not set, LocalAuthentication will ask for the password when necessary. It will use
/// its own user interface depending on the evaluated policy or ACL.
/// Applications can provide the password using the setCredential method. In such case,
/// LocalAuthentication will not show password entry user interface.
/// When entered from the LocalAuthentication user interface, the password is stored as
/// UTF-8 encoded string.
LACredentialTypeApplicationPassword __TVOS_UNAVAILABLE = 0,
} NS_ENUM_AVAILABLE(10_11, 9_0) __WATCHOS_AVAILABLE(3.0) __TVOS_AVAILABLE(10.0);
/// Sets a credential to this context.
///
/// @discussion Some policies allow to bind application-provided credential with them.
/// This method allows credential to be passed to the right context.
///
/// @param credential Credential to be used with subsequent calls. Setting this parameter to nil will remove
/// any existing credential of the specified type.
///
/// @param type Type of the provided credential.
///
/// @return YES if the credential was set successfully, NO otherwise.
///
- (BOOL)setCredential:(nullable NSData *)credential
type:(LACredentialType)type NS_AVAILABLE(10_11, 9_0) __WATCHOS_AVAILABLE(3.0) __TVOS_UNAVAILABLE;
/// Reveals if credential was set with this context.
///
/// @param type Type of credential we are asking for.
///
/// @return YES on success, NO otherwise.
///
- (BOOL)isCredentialSet:(LACredentialType)type NS_AVAILABLE(10_11, 9_0) __WATCHOS_AVAILABLE(3.0) __TVOS_UNAVAILABLE;
typedef NS_ENUM(NSInteger, LAAccessControlOperation)
{
/// Access control will be used for item creation.
LAAccessControlOperationCreateItem,
/// Access control will be used for accessing existing item.
LAAccessControlOperationUseItem,
/// Access control will be used for key creation.
LAAccessControlOperationCreateKey,
/// Access control will be used for sign operation with existing key.
LAAccessControlOperationUseKeySign,
/// Access control will be used for data decryption using existing key.
LAAccessControlOperationUseKeyDecrypt NS_ENUM_AVAILABLE(10_12, 10_0),
/// Access control will be used for key exchange.
LAAccessControlOperationUseKeyKeyExchange NS_ENUM_AVAILABLE(10_12, 10_0),
} NS_ENUM_AVAILABLE(10_11, 9_0) __WATCHOS_AVAILABLE(3.0) __TVOS_AVAILABLE(10.0);
/// Evaluates access control object for the specified operation.
///
/// @discussion Access control evaluation may involve prompting user for various kinds of interaction
/// or authentication. Actual behavior is dependent on evaluated access control, device type,
/// and can be affected by installed configuration profiles.
///
/// Be sure to keep a strong reference to the context while the evaluation is in progress.
/// Otherwise, an evaluation would be canceled when the context is being deallocated.
///
/// The method does not block. Instead, the caller must provide a reply block to be
/// called asynchronously when evaluation finishes. The block is executed on a private
/// queue internal to the framework in an unspecified threading context. Other than that,
/// no guarantee is made about which queue, thread, or run-loop the block is executed on.
///
/// After successful access control evaluation, the LAContext can be used with keychain operations,
/// so that they do not require user to authenticate.
///
/// Access control evaluation may fail for various reasons, including user cancel, system cancel
/// and others, see LAError codes.
///
/// @param accessControl Access control object that is typically created by SecAccessControlCreateWithFlags.
///
/// @param operation Type of operation the access control will be used with.
///
/// @param localizedReason Application reason for authentication. This string must be provided in correct
/// localization and should be short and clear. It will be eventually displayed in
/// the authentication dialog. A name of the calling application will be already
/// displayed in title, so it should not be duplicated here.
///
/// @param reply Reply block that is executed when access control evaluation finishes.
/// success Reply parameter that is YES if the access control has been evaluated successfully or
/// NO if the evaluation failed.
/// error Reply parameter that is nil if the access control has been evaluated successfully, or
/// it contains error information about the evaluation failure.
///
/// @warning localizedReason parameter is mandatory and the call will throw NSInvalidArgumentException if
/// nil or empty string is specified.
- (void)evaluateAccessControl:(SecAccessControlRef)accessControl
operation:(LAAccessControlOperation)operation
localizedReason:(NSString *)localizedReason
reply:(void(^)(BOOL success, NSError * __nullable error))reply
NS_AVAILABLE(10_11, 9_0) __WATCHOS_AVAILABLE(3.0) __TVOS_UNAVAILABLE;
/// Fallback button title.
/// @discussion Allows fallback button title customization. A default title "Enter Password" is used when
/// this property is left nil. If set to empty string, the button will be hidden.
@property (nonatomic, nullable, copy) NSString *localizedFallbackTitle;
/// Cancel button title.
/// @discussion Allows cancel button title customization. A default title "Cancel" is used when
/// this property is left nil or is set to empty string.
@property (nonatomic, nullable, copy) NSString *localizedCancelTitle NS_AVAILABLE(10_12, 10_0);
/// Allows setting the limit for the number of failures during biometric authentication.
///
/// @discussion When the specified limit is exceeded, evaluation of LAPolicyDeviceOwnerAuthenticationWithBiometrics
/// evaluation will fail with LAErrorAuthenticationFailed. By default this property is nil and
/// the biometric authentication fails after 3 wrong attempts.
///
/// @warning Please note that setting this property with high values does not prevent biometry lockout after 5
/// wrong attempts.
@property (nonatomic, nullable) NSNumber *maxBiometryFailures NS_DEPRECATED_IOS(8_3, 9_0) __WATCHOS_UNAVAILABLE __TVOS_UNAVAILABLE;
/// Contains policy domain state.
///
/// @discussion This property is set only when evaluatePolicy is called and succesful Touch ID authentication
/// was performed, or when canEvaluatePolicy succeeds for a biometric policy.
/// It stays nil for all other cases.
/// If finger database was modified (fingers were removed or added), evaluatedPolicyDomainState
/// data will change. Nature of such database changes cannot be determined
/// but comparing data of evaluatedPolicyDomainState after different evaluatePolicy
/// will reveal the fact database was changed between calls.
/// @warning Please note that the value returned by this property can also change between OS versions even if
/// there was no change of the enrolled fingerprints.
//就是说这个值只是用来判断指纹数据库是否有改变，如果有改变，那么这个值会不为空，然后我们根据这个值来判断，而且要注意这个值在系统版本升级的时候也会改变。 一般开发不会使用到
@property (nonatomic, nullable, readonly) NSData *evaluatedPolicyDomainState NS_AVAILABLE(10_11, 9_0) __WATCHOS_UNAVAILABLE __TVOS_UNAVAILABLE;
/// Time interval for accepting a successful Touch ID device unlock (on the lock screen) from the past.
///
/// @discussion This property can be set with a time interval in seconds. If the device was successfully unlocked by
/// Touch ID within this time interval, then Touch ID authentication on this context will succeed
/// automatically and the reply block will be called without prompting user for Touch ID.
///
/// The default value is 0, meaning that no previous TouchID unlock can be reused.
///
/// This property is meant only for reusing Touch ID matches from the device lock screen.
/// It does not allow reusing previous Touch ID matches in application or between applications.
///
/// The maximum supported interval is 5 minutes and setting the value beyond 5 minutes does not increase
/// the accepted interval.
///
/// @see LATouchIDAuthenticationMaximumAllowableReuseDuration
@property (nonatomic) NSTimeInterval touchIDAuthenticationAllowableReuseDuration NS_AVAILABLE(NA, 9_0) __WATCHOS_UNAVAILABLE __TVOS_UNAVAILABLE;
@end
NS_ASSUME_NONNULL_END
在日常开发中 一般先调用
- (BOOL)canEvaluatePolicy:(LAPolicy)policy error:(NSError * __autoreleasing *)error __attribute__((swift_error(none)));
来判断是否可以调用指纹识别，错误有
LAErrorAuthenticationFailed = kLAErrorAuthenticationFailed,
/// Authentication was canceled by user (e.g. tapped Cancel button). //取消按钮
LAErrorUserCancel = kLAErrorUserCancel,
/// Authentication was canceled, because the user tapped the fallback button (Enter Password). //点击输入密码的按钮
LAErrorUserFallback = kLAErrorUserFallback,
/// Authentication was canceled by system (e.g. another application went to foreground). //被系统退出
LAErrorSystemCancel = kLAErrorSystemCancel,
/// Authentication could not start, because passcode is not set on the device. //没有设置密码
LAErrorPasscodeNotSet = kLAErrorPasscodeNotSet,
/// Authentication could not start, because Touch ID is not available on the device. //该设备不支持TouchID
LAErrorTouchIDNotAvailable = kLAErrorTouchIDNotAvailable,
/// Authentication could not start, because Touch ID has no enrolled fingers. //没有设置指纹密码
LAErrorTouchIDNotEnrolled = kLAErrorTouchIDNotEnrolled,
/// 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) __WATCHOS_AVAILABLE(3.0) __TVOS_AVAILABLE(10.0) = kLAErrorTouchIDLockout,
/// Authentication was canceled by application (e.g. invalidate was called while
/// authentication was in progress). //失败次数太多
LAErrorAppCancel NS_ENUM_AVAILABLE(10_11, 9_0) = kLAErrorAppCancel,
/// LAContext passed to this call has been previously invalidated. //LAContext执行到这里的时候 失效了
LAErrorInvalidContext NS_ENUM_AVAILABLE(10_11, 9_0) = kLAErrorInvalidContext
一般来说 开发者只需要 处理好 unset没有设置的情况，其他情况都可以处理为失败的情况，执行对应的逻辑操作即可
如果可以正常使用指纹识别的话，那么接下来只需要调用
- (void)evaluatePolicy:(LAPolicy)policy localizedReason:(NSString *)localizedReason reply:(void(^)(BOOL success, NSError * __nullable error))reply;
即可唤起指纹识别，根据reply来判断指纹识别的成功与否
特别提醒这里，如果多次输错然后需要输入手机密码的时候，输入成功是不会success的，依然需要指纹识别成功才会success
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