Introduction to HealthKit: Reading Steps, Weight, Height, and More

Project Objectives

I was instructed to integrate HealthKit information — specifically pulling steps data — into Breathometer's upcoming app. I'm realitively new to Swift having only started a month ago, so this project was a way for me to get more familiar with the language and IDE. My task was to pull the data from HealhtKit then populate a table within a page of the app. This data could then be used for visualizations, analysis, etc. Here are my main learning goals for this project:

• Learn how to integrate with HealthKit and pull data from a “3rd party” source (not really a 3rd party but it's an API all the same)
• Learn the fundamentals of table views, populating views, etc. so that I can develop a better understanding of Swift frontend see next post

Authorizing and Integrating with HealthKit

Nested within the authorizeHealthKit function:

1func authorizeHealthKit(completion: ((success:Bool, error:NSError!) -> Void)!) {
2}
3

Get Healthkit information to read

1let healthKitTypesToRead = NSSet(objects:
2  HKObjectType.characteristicTypeForIdentifier(HKCharacteristicTypeIdentifierDateOfBirth)!, HKObjectType.characteristicTypeForIdentifier(HKCharacteristicTypeIdentifierBiologicalSex)!,
3  HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierHeight)!,
4  HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierBodyMass)!
5)
6

Healthkit information to write

1let healthKitTypesToWrite = NSSet(objects:
2            HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierBodyMass)!
3        )
4

To actually get data from healthkit, create a function within the class. This one, for example, gets your birthdate from health kit:

1func getBirthdateFromHealthKit() -> AnyObject {
2        var birthdate: AnyObject!
3        do {
4            birthdate = try healthKitStore.dateOfBirth()
5        } catch {
6            print("No birthday listed, or permission denied")
7            birthdate = "Not Set"
8        }
9
10        return birthdate
11    }
12

More complex example

Pulls steps from Healthkit (x number of days) and show it in a table view by creating a new function within the HealthKitManager class.

Returning steps by per day for x number of days:

1func readStepsByDay(sinceDaysAgo: Int, completion: (([HKQuantitySample]!, NSError!) -> Void)!) {
2        let type: HKQuantityType = HKQuantityType.quantityTypeForIdentifier(HKQuantityTypeIdentifierStepCount)!
3        let currentDate = NSDate().dateWithoutTime() // Get current date
4
5        var stepData: [HKQuantitySample] = []
6
7        for daysAgo in 1...sinceDaysAgo {
8            let startDate: NSDate = currentDate.daysAgo(daysAgo) // Set start date
9            let endDate: NSDate = currentDate.daysAgo(daysAgo - 1) // Next day
10            let predicate = HKQuery.predicateForSamplesWithStartDate(startDate, endDate: endDate, options: .None) // Set parameters
11            // Getting all step counts within that day
12            let sampleQuery = HKStatisticsQuery(quantityType: type, quantitySamplePredicate: predicate, options: [.CumulativeSum], completionHandler: { (sampleQuery, result, error ) -> Void in
13
14                if let queryError = error {
15                    completion(nil, queryError) // End the master function
16                    print("Completion nil")
17                    return
18                }
19                if completion != nil {
20                    // Create KHQuantitySample for this day
21                    let units = HKUnit.countUnit()
22                    var quantity: HKQuantity = HKQuantity(unit: units, doubleValue: 0.0)
23                    if let value = result?.sumQuantity()?.doubleValueForUnit(HKUnit.countUnit()) {
24                        quantity = HKQuantity(unit: units, doubleValue: value)
25                    }
26                    let currentData = HKQuantitySample(type: HKQuantityType.quantityTypeForIdentifier(HKQuantityTypeIdentifierStepCount)!, quantity: quantity, startDate: startDate, endDate: endDate) // Initiate HKQuantitySample
27                    stepData.append(currentData) // Add data to array
28
29                    if stepData.count == sinceDaysAgo { // If got all data
30                        // If all days are properly fetched -> return [HKQuanitity] sample to master function
31                        stepData.sortInPlace({ // Sort by time
32                            $0.0.startDate.timeIntervalSinceNow > $0.1.startDate.timeIntervalSinceNow
33                        })
34                        completion(stepData, nil) // Return error free
35                    }
36                }
37            })
38
39            self.healthKitStore.executeQuery(sampleQuery) // Fire the call
40        }
41    }
42

Extensions Used

1extension NSDate {
2    func daysAgo(daysAgo: Int) -> NSDate {
3        let result = -24 *60* 60 * Double(daysAgo)
4        return self.dateByAddingTimeInterval(result)
5    }
6
7    func dateWithoutTime() -> NSDate {
8        let dateFormatter = NSDateFormatter()
9        dateFormatter.dateStyle = .MediumStyle // Doesn't include time component
10        let dateToPrint: NSString = dateFormatter.stringFromDate(self) as NSString // Format into medium style string
11        let dateNoTime = dateFormatter.dateFromString(dateToPrint as String) // Get a date from midnight that day
12        return dateNoTime!
13    }
14}
15

Usage

1HealthKitManager().readStepsByDay(100, completion: { (mostRecentSteps, error) in
2
3            // Catch error
4            if( error != nil ) {
5                print("Error reading weight from HealthKit Store: \(error.localizedDescription)") // Feedback
6                return // End function
7            }
8
9            for dayCount in mostRecentSteps {
10                print(dayCount.quantity.doubleValueForUnit(HKUnit.countUnit()))
11            }
12        })
13