iOS 未从返回的 block 中看到预期值

Question

我有以下代码，但我从未看到 runStepCountTotal 最后返回。总增量，但最后一个 NSLog 行实际上是在 block 完成之前返回的。

我意识到我错误地使用了该 block ，但想知道是否有人愿意向我解释如何实现这一目标？

非常感谢。

- (NSInteger)getRunSteps
{
__block NSInteger runstepCountTotal = 0;

if([CMMotionActivityManager isActivityAvailable])
{
    CMMotionActivityManager *cm = [[CMMotionActivityManager alloc] init];
    CMStepCounter *sc = [[CMStepCounter alloc] init];
    NSDate *today = [NSDate date];
    [cm queryActivityStartingFromDate:[self startDateOf6DayAgo] toDate:today toQueue:[NSOperationQueue mainQueue] withHandler:^(NSArray *activities, NSError *error){

        for(int i=0;i<[activities count]-1;i++)
        {
            CMMotionActivity *a = [activities objectAtIndex:i];
            if (a.running)
            {
                [sc queryStepCountStartingFrom:a.startDate to:[[activities objectAtIndex:i+1] startDate] toQueue:[NSOperationQueue mainQueue] withHandler:^(NSInteger numberOfSteps, NSError *error)
                {
                    runstepCountTotal = runstepCountTotal+numberOfSteps;
                    NSLog(@"Current Total is %ld",(long)runstepCountTotal);
                }];
            }
        }
    }];
}
NSLog(@"Final Total is %ld",(long)runstepCountTotal);
return runstepCountTotal;
}

Answer 1

阅读有关 queryActivityStartingFromDate:toDate:toQueue:withHandler: 方法的文档。

Discussion
This method runs asynchronously, returning immediately and delivering the results to the specified handler block.

您的方法在调用和完成处理程序 block 之前很久就返回了。