功能需求：登錄之后，只要不退出登錄，再次進入app時需要驗證指紋后進入主頁面。

- (void)viewDidLoad {
    [super viewDidLoad];
    [self showFingerprintVerification];
}

// 指紋驗證
- (void)showFingerprintVerification {
    
    // 初始化上下文對象
    LAContext *context = [[LAContext alloc] init];
    
    // 錯誤對象
    NSError *error = nil;
    NSString *result = @"通過Home鍵驗證已有手機指紋";
    
    // 首先使用canEvaluatePolicy 判斷設(shè)備支持狀態(tài)
    if ([context canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&error]) {
        
        // 支持指紋驗證
        [context evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics localizedReason:result  reply:^(BOOL success, NSError *error) {
            if (success) {

                NSLog(@"登錄成功");
                [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                    [[AppDelegate sharedAppDelegate] changeMainRootViewController];

                }];
                
            } else {
                NSLog(@"%@",error.localizedDescription);
                switch (error.code) {
                        
                    case LAErrorSystemCancel: {
                        NSLog(@"切換到其他APP，系統(tǒng)取消驗證Touch ID");
                        break;
                    }
                    case LAErrorUserCancel: {
                        NSLog(@"用戶取消驗證Touch ID");
                        break;
                    }
                    case LAErrorUserFallback: {
                        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                            NSLog(@"用戶選擇輸入密碼，切換主線程處理");
                            
                            // 登錄頁面
                            NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
                            [userDefaults setInteger:unLogin forKey:FYLOGINTIMES_Key];
                            [userDefaults synchronize];
                            [[AppDelegate sharedAppDelegate] changeRootViewController];
                        }];
                        break;
                    }
                    case LAErrorTouchIDLockout: { // iOS 9之后才會有的
                        
                        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                            NSLog(@"多次指紋校驗失敗, 需要輸入密碼解鎖");

                            UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"指紋不匹配" message:nil preferredStyle:UIAlertControllerStyleAlert];
                            [self presentViewController:alert animated:NO completion:nil];
                            
                            dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 2.0 *NSEC_PER_SEC);
                            dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
                                [alert dismissViewControllerAnimated:YES completion:nil];
                            });
                        }];
                        break;
                    }
                    case LAErrorAppCancel: {      // iOS 9之后才會有的
                        NSLog(@"當前app被掛起取消了授權(quán),和LAErrorSystemCancel不太一樣");
                        break;
                    }
                    case LAErrorInvalidContext: { // iOS 9之后才會有的
                        NSLog(@"LAContext對象被釋放掉了，造成的授權(quán)失敗");
                        break;
                    }
                    default: {
                        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                            
                        }];
                        break;
                    }
                }
            }
        }];
    } else {
        // 不支持指紋識別，LOG出錯誤詳情
        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);
    }
}