How to Wait for Asynchronous Function Swift

Question

I have a function that gathers step data, but I need a way to make it wait for its query to finish before it loops. I realize there are other questions about this problem, but I can't figure out how to fix it. The function is below:

func stepsAllTime(completion: (Double, NSError?) -> () ) {
    var stopStart = true
    while stopStart {

        x += -1
        // The type of data we are requesting
        let sampleType = HKSampleType.quantityTypeForIdentifier(HKQuantityTypeIdentifierStepCount)
        var daysAgo = x
        var daysSince = x + 1
        var daysSinceNow = -1 * daysAgo
        checker = allTimeSteps.count

        // Our search predicate which will fetch data from now until a day ago
        let samplePredicate = HKQuery.predicateForSamplesWithStartDate(NSCalendar.currentCalendar().dateByAddingUnit(.CalendarUnitDay, value: daysAgo, toDate: NSDate(), options: nil), endDate: NSCalendar.currentCalendar().dateByAddingUnit(.CalendarUnitDay, value: daysSince, toDate: NSDate(), options: nil), options: .None)

        // The actual HealthKit Query which will fetch all of the steps and sub them up for us.
        let stepQuery = HKSampleQuery(sampleType: sampleType, predicate: samplePredicate, limit: 0, sortDescriptors: nil) { query, results, error in
            var steps: Double = 0


            if results?.count > 0 {
                for result in results as! [HKQuantitySample] {
                    steps += result.quantity.doubleValueForUnit(HKUnit.countUnit())
                }
            }

            completion(steps, error)
            self.allTimeStepsSum += steps
            self.allTimeSteps.append(steps)
            println("New Sum:")
            println(self.allTimeStepsSum)
            println("Days Since Today:")
            println(daysSinceNow)
            if !(self.allTimeStepsTotal > self.allTimeStepsSum) {
                stopStart = false
            }
        }
        if allTimeStepsTotal > allTimeStepsSum {

            self.healthKitStore.executeQuery(stepQuery)

        }

    }

}

How can this be done? Is there some sort of "On Complete" function in Swift?

Just to be clear... you want your stepQuery completion closure to be called before your next while stopStart pass executes? — bsarrazin
– bsarrazin, Commented Jul 21, 2015 at 23:39

bsarrazin · Accepted Answer · 2015-07-22 00:13:31Z

1

I'm assuming that my comment was accurate. You'd probably want to take a look at a recursive pattern, something like this:

import HealthKit

class Person {

    var nbSteps: Double = 0

    func fetchInfo() -> Void {
        let sampleType = HKSampleType()
        let samplePredicate: NSPredicate? = nil // Your predicate
        let stepQuery = HKSampleQuery(
            sampleType: sampleType,
            predicate: samplePredicate,
            limit: 0,
            sortDescriptors: nil) { (sampleQuery, object, error) -> Void in
                self.nbSteps += 1 // or the value you're looking to add

                dispatch_async(dispatch_get_main_queue(), { () -> Void in // Dispatch in order to keep things clean
                    self.fetchInfo()
                })
        }
    }

}

answered Jul 22, 2015 at 0:13

bsarrazin

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Comments

Shibu Thannikkunnath · Accepted Answer · 2015-07-21 23:34:42Z

1

You can make the program to wait till the query finishes by implementing callbacks.

You can read more about it in the following blog post http://www.charles-socrates-chandler.com/blog/2015/2/10/callbacks-in-swift

answered Jul 21, 2015 at 23:34

Shibu Thannikkunnath

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1 Comment

ButtonMasterBot Over a year ago

In case you haven't noticed, I already have this in my function, and it hasn't helped.

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