面试题：Objective-C的Health App数据集成之优化与安全

性能优化策略及代码示例

数据缓存
- 策略：使用NSCache来缓存HealthKit获取的数据，减少重复获取的开销。NSCache是一个自动释放内存的缓存，当系统内存不足时会自动释放缓存对象。
- 代码示例：

// 创建一个全局的NSCache实例
static NSCache *healthKitCache;

@implementation HealthDataManager

+ (void)initialize {
    if (self == [HealthDataManager class]) {
        healthKitCache = [[NSCache alloc] init];
    }
}

- (NSArray *)fetchHealthDataWithSampleType:(HKObjectType *)sampleType predicate:(NSPredicate *)predicate {
    NSArray *cachedData = [healthKitCache objectForKey:sampleType];
    if (cachedData) {
        return cachedData;
    }
    
    // 如果缓存中没有，从HealthKit获取数据
    HKHealthStore *healthStore = [[HKHealthStore alloc] init];
    [healthStore executeQuery:[[HKQuery alloc] initWithSampleType:sampleType predicate:predicate limit:HKObjectQueryNoLimit sortDescriptors:nil resultsHandler:^(HKQuery * _Nonnull query, NSArray<__kindof HKSample *> * _Nullable results, NSError * _Nullable error) {
        if (results) {
            [healthKitCache setObject:results forKey:sampleType];
        }
    }]];
    
    return cachedData;
}

@end

异步加载
- 策略：利用Grand Central Dispatch (GCD)将HealthKit数据获取操作放到后台队列执行，避免阻塞主线程，保证应用的流畅性。
- 代码示例：

- (void)fetchHealthDataAsynchronouslyWithSampleType:(HKObjectType *)sampleType predicate:(NSPredicate *)predicate completion:(void(^)(NSArray<__kindof HKSample *> *results, NSError *error))completion {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        HKHealthStore *healthStore = [[HKHealthStore alloc] init];
        [healthStore executeQuery:[[HKQuery alloc] initWithSampleType:sampleType predicate:predicate limit:HKObjectQueryNoLimit sortDescriptors:nil resultsHandler:^(HKQuery * _Nonnull query, NSArray<__kindof HKSample *> * _Nullable results, NSError * _Nullable error) {
            dispatch_async(dispatch_get_main_queue(), ^{
                completion(results, error);
            });
        }]];
    });
}

隐私安全策略及代码示例

数据加密
- 策略：使用Common Crypto框架对敏感的HealthKit数据进行加密。例如，对于心率数据，可以在存储到本地缓存或者传输到服务器之前进行加密。
- 代码示例：

#import <CommonCrypto/CommonCrypto.h>

- (NSData *)encryptData:(NSData *)data withKey:(NSData *)key {
    char keyPtr[kCCKeySizeAES256 + 1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getBytes:keyPtr length:MIN(key.length, sizeof(keyPtr) - 1)];
    
    char ivPtr[kCCBlockSizeAES128 + 1];
    bzero(ivPtr, sizeof(ivPtr));
    NSData *iv = [NSData dataWithBytes:ivPtr length:kCCBlockSizeAES128];
    
    size_t encryptedDataLength = 0;
    size_t bufferSize = data.length + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, iv.bytes, data.bytes, data.length, buffer, bufferSize, &encryptedDataLength);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:encryptedDataLength];
    }
    free(buffer);
    return nil;
}

权限管理
- 策略：在访问HealthKit数据之前，明确请求用户授权，并且根据应用的需求合理请求权限。例如，只请求读取心率和步数权限，而不是请求所有权限。
- 代码示例：

HKHealthStore *healthStore = [[HKHealthStore alloc] init];
HKObjectType *heartRateType = [HKObjectType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate];
HKObjectType *stepCountType = [HKObjectType quantityTypeForIdentifier:HKQuantityTypeIdentifierStepCount];
NSSet *healthKitTypesToRead = [NSSet setWithObjects:heartRateType, stepCountType, nil];

[healthStore requestAuthorizationToShareTypes:nil readTypes:healthKitTypesToRead completion:^(BOOL success, NSError * _Nullable error) {
    if (success) {
        // 权限请求成功，可以进行数据读取
    } else {
        // 权限请求失败，处理错误
    }
}];

星途面试题库

面试题：Objective-C的Health App数据集成之优化与安全

知识考点

面试题答案

性能优化策略及代码示例

隐私安全策略及代码示例