运行一些代码使用不同的变量多次异步

Question

所以，我正在尝试让我的应用程序读取 HealthKit 数据。我有一个从主应用程序视图控制器调用的函数，它会在另一个 class 中查询该月的所有健康数据。在数据数组从计算 class 中的单独函数 return 到视图控制器中的单独函数之前，需要进行一些计算。

由于数据量大，每次查询大约需要 2 秒。我希望能够异步关闭它们，当它们全部 returned 时，我可以更新 UI.

问题是，我每个月都调用该函数，它会启动 HKSampleQueries，但它们没有按顺序 return，而且它们需要花费时间return 各不相同。这意味着我最终在一组数据计算的中途更改了变量，因为下一组数据刚刚开始。

我只知道两种解决方法：

像这样调用每个计算之前设置延迟：

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 3 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{}

但这会浪费应用时间

或者我可以多次复制代码并为每个月调用不同的 class。但这似乎愚蠢且效率低下。

所以问题是。我如何有效地共享每次将运行与不同变量多次的代码。干杯

函数示例：

在视图控制器中：

HeartRateCalculator *commonClassTwo =[[HeartRateCalculator alloc] init];
[commonClassTwo calculateData:0];
[commonClassTwo calculateData:-1];
[commonClassTwo calculateData:-2];

在心率计算器中

-(void)calculateData:(NSInteger)monthsBack{
  //Some other stuff
//Generate monthPeriodPredicate based on monthsBack integer
  HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:heartRate predicate:monthPeriodPredicate limit:200000 sortDescriptors:@[timeSortDescriptor] resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) {
  //Finish Calculations, call other functions (ie. [self doThis];) and then return
//When calculations return, monthPeriodPredicate is always value of the last predicate to be called, not the one that the HKSampleQuery was made with.
}
[healthStoreFive executeQuery:query];

完整代码：

-(void)calculateData:(NSInteger)monthsBack withCompletionBlock:(void(^)())completionBlock {//0 Means only current month, 2 means this month and last month and month before
//for(NSInteger i=0; i>=monthsBack; i--){
    //monthForCalculation = monthsBack;
    NSDateComponents *components = [[NSCalendar currentCalendar] components: NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond fromDate:[NSDate date]];
    NSDateComponents *adjustableComponent = [[NSDateComponents alloc] init];
    [adjustableComponent setMonth:monthsBack];
    [adjustableComponent setDay:-[components day]+1];
    [adjustableComponent setHour:-[components hour]];
    [adjustableComponent setMinute:-[components minute]];
    [adjustableComponent setSecond:-[components second]];
    startOfMonth = [[NSCalendar currentCalendar] dateByAddingComponents:adjustableComponent toDate:[NSDate date] options:0];
    adjustableComponent = [[NSDateComponents alloc] init];
    [adjustableComponent setMonth:1];
    NSDate *endOfMonth = [[NSCalendar currentCalendar] dateByAddingComponents:adjustableComponent toDate:startOfMonth options:0];

    NSDate *secondEarlier = [endOfMonth dateByAddingTimeInterval:-1];
    components = [[NSCalendar currentCalendar] components: NSCalendarUnitDay fromDate:secondEarlier];
    daysInMonth = [components day];

    NSPredicate *monthPeriodPredicate = [HKQuery predicateForSamplesWithStartDate:startOfMonth endDate:endOfMonth options:HKQueryOptionStrictStartDate];
    healthStoreFive = [[HKHealthStore alloc] init];
    HKQuantityType *heartRate = [HKObjectType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate];
    NSSortDescriptor *timeSortDescriptor = [[NSSortDescriptor alloc] initWithKey:HKSampleSortIdentifierEndDate ascending:NO];
    HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:heartRate predicate:monthPeriodPredicate limit:200000 sortDescriptors:@[timeSortDescriptor] resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) {
        NSMutableArray *dataValues = [[NSMutableArray alloc] init];
        NSMutableArray *dataDates = [[NSMutableArray alloc] init];
        for (HKQuantitySample *sample in results) {
            [dataValues addObject:[NSNumber numberWithFloat:[sample.quantity doubleValueForUnit:[[HKUnit countUnit] unitDividedByUnit:[HKUnit minuteUnit]]]]];
            [dataDates addObject:sample.startDate];
        }
        monthForCalculation = monthsBack;
        chronologicalDataValues = [[NSMutableArray alloc] init];
        chronologicalDataDates = [[NSMutableArray alloc] init];
        chronologicalDataValues = [[[dataValues reverseObjectEnumerator] allObjects] mutableCopy];
        chronologicalDataDates = [[[dataDates reverseObjectEnumerator] allObjects] mutableCopy];          
        //dispatch_async(dispatch_get_main_queue(), ^{
            if(dataDates.count == 0){
                ViewController *commonClass =[[ViewController alloc] init];
                [commonClass receiveCalculationData:[[NSMutableArray alloc] init] array:[[NSMutableArray alloc] init] daysToDisplay:[[NSMutableArray alloc] init] chosenMonth:monthForCalculation];
            }
            else{
                NSLog(@"%@", [dataDates objectAtIndex:dataDates.count-1]);
                NSLog(@"%@", [dataDates objectAtIndex:0]);
                [self calculateDayStringsFromData];
            }

            completionBlock();
        //});
    }];
    NSLog(@"HKSampleQuery Requested For Heart Rate Data");
    [healthStoreFive executeQuery:query];

// } }

Answer 1

使用block

[commonClassTwo calculateData:0 withCompletionBlock:^{
    [commonClassTwo calculateData:-1 withCompletionBlock:^{
        [commonClassTwo calculateData:-2 withCompletionBlock:^{
            NSLog(@"All 3 calculation done");
        }];
    }];
}];

- (void)calculateData:(NSInteger)monthsBack withCompletionBlock:(void(^)())completionBlock {
    //Some other stuff
    HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:heartRate predicate:monthPeriodPredicate limit:200000 sortDescriptors:@[timeSortDescriptor] resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) {
        //Finish Calculations, call other functions (ie. [self doThis];) and then return
        completionBlock();
    }
    [healthStoreFive executeQuery:query];
}

更新

对于异步调用，有一个计数器 integer。初始值将是您想要的异步调用的数量。（此处 3）
在每次调用的 completionBlock 中，递减计数器并检查所有调用是否完成。
如果完成更新 UI。

[commonClassTwo calculateData:0 withCompletionBlock:^{
    // counter--;
    // [self updateUI];
}];

[commonClassTwo calculateData:-1 withCompletionBlock:^{
    // counter--;
    // [self updateUI];
}];

[commonClassTwo calculateData:-2 withCompletionBlock:^{
    // counter--;
    // [self updateUI];
}];

- (void)updateUI {
    // if counter == 0 {
    //     dispatch_async(dispatch_get_main_queue(), ^{
    //         update UI
    //     });
    // }
}

Answer 2

您可以制作单独的 class 并同时运行它们。

HeartRateCalculator *commonClassOne =[[HeartRateCalculator alloc] init];
HeartRateCalculator *commonClassTwo =[[HeartRateCalculator alloc] init];
HeartRateCalculator *commonClassThree =[[HeartRateCalculator alloc] init];
[commonClassOne calculateData:0];
[commonClassTwo calculateData:-1];
[commonClassThree calculateData:-2];

这样您就不必复制代码，但它们不会覆盖相同 class 中的值。

Answer 3

您可以使用 dispatch_group 来安排一个块在您完成所有任务后触发。

您只需修改 calculateData: 方法以接受 dispatch_group_t 参数（如果需要，您也可以随时添加完成块）：

- (void)calculateData:(NSInteger)monthsBack group:(dispatch_group_t)group {

    dispatch_group_enter(group); // increment group task count

    //Some other stuff

    HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:heartRate predicate:monthPeriodPredicate limit:200000 sortDescriptors:@[timeSortDescriptor] resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) {

        //Finish Calculations, call other functions (ie. [self doThis];) and then return

        dispatch_group_leave(group); // decrement task count
    }];

    [healthStoreFive executeQuery:query];

}

那你就可以这样称呼它了:

HeartRateCalculator *commonClassTwo =[[HeartRateCalculator alloc] init];

dispatch_group_t group = dispatch_group_create();

[commonClassTwo calculateData:0 group:group];
[commonClassTwo calculateData:-1 group:group];
[commonClassTwo calculateData:-2 group:group];

dispatch_group_notify(group, dispatch_get_main_queue(), ^{ // called when all tasks are finished.
    // update UI
});

与的原理相同，但dispatch_groups比使用您自己的变量来跟踪执行的任务数更优雅。

虽然我不太清楚你说的要让任务异步执行是什么意思。来自 Apple docs on HKSampleQuery:

Queries run on an anonymous background queue.

因此您的任务已经异步。

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