CODEWITHSUNDEEP
iosswifthealthkit
Eric
Eric

Reputation: 5215

Data from HealthKit is initially missing, then comes in when I try again - how to fix?

I have an iOS app that I'm developing in Swift, and as part of the app it gathers the step count for the current day.

The first time I run the app, the count is "0", but if I click a button in the interface to re-run this function that queries HK, then the correct number appears.

I am guessing this is because HK needs some time to gather the data, or something, but I'm not sure how to fix it. Maybe HK can fire an event when the data is ready, and then I can update the UI?

Here's the routine that gathers the data from HK. This function executes immediately when the app start (and it shows "0 steps today"), and then as I describe above, I can tap a button to execute the function again (and then I get the right number).

    func queryStepsSum() {
        // prepare HK for the data
        let endDate = NSDate()          // right now
        let startDate = NSCalendar.currentCalendar().dateBySettingHour(0, minute: 0, second: 0, ofDate: endDate, options: NSCalendarOptions())
        let predicate = HKQuery.predicateForSamplesWithStartDate(startDate, endDate: endDate, options: .None)
        let sumOption = HKStatisticsOptions.CumulativeSum
        let statisticsSumQuery = HKStatisticsQuery( quantityType: self.stepsCount!, quantitySamplePredicate: predicate,
                                                    options: sumOption)
        { [unowned self] (query, result, error) in
            if let sumQuantity = result?.sumQuantity() {
                self.numberOfSteps = Int(sumQuantity.doubleValueForUnit(HKUnit.countUnit()))
            }
        }

        // run the HK query
        self.healthStore?.executeQuery(statisticsSumQuery)

        // update the UI with the result
        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            self.stepsLabel.text = "\(self.numberOfSteps) steps today";
        });
    }

Upvotes: 2

Views: 374

Answers (2)

Allan
Allan

Reputation: 7343

Your code doesn't wait for the query to finish before displaying the result (the query happens asynchronously). You should update your UI from the query's result handler, like this: 

    let statisticsSumQuery = HKStatisticsQuery( quantityType: self.stepsCount!, quantitySamplePredicate: predicate,
                                                options: sumOption)
    { [unowned self] (query, result, error) in
        dispatch_async(dispatch_get_main_queue()) {
            if let sumQuantity = result?.sumQuantity() {
                self.numberOfSteps = Int(sumQuantity.doubleValueForUnit(HKUnit.countUnit()))
                self.stepsLabel.text = "\(self.numberOfSteps) steps today";
            }
        }
    }

Also note that I've included a dispatch back to the main thread since the query results handler runs on a background thread and it's not safe to manipulate UI in that context.

Upvotes: 2

Preston Price
Preston Price

Reputation: 325

Are you calling your function in viewDidLoad? You might try calling it in viewDidAppear instead. If that doesn't work maybe there is some sort of delegate method that can update you when the data is ready like you said. I've never worked with HealthKit but I'll check to see if I can find anything.

EDIT: This might set the UI component off the background thread. Try:

var numberOfSteps: Int! {
    didSet {
        self.stepsLabel.text = "\(self.numberOfSteps) steps today"
    }
}

That should get rid of the error that you're updating the UI on the background thread. Also make sure to remove your call in the closure that I told you to put.

Upvotes: 0

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