CODEWITHSUNDEEP
swiftuicombine
Bjorn Morrhaye
Bjorn Morrhaye

Reputation: 731

Combine asynchronous return values in SwiftUI

I have 2 asynchronous return values from 2 different classes, one from HealthKit, the other from MotionManager. My goal is to combine these values and output them in a swiftui View, where it refreshes every second. I know I have to look at the combine framework here, but I don't know where to start. I can't find a lot of tutorials which describe Swiftui + Combine. I know I have to look at .combineLatest but do I have to write my own Publisher and Subscriber, or can I use @Published property wrapper I have here (@Published var motionData = MotionData() and @Published var heartRateValue: Double = 0.0) ?

My MotionManager Class:

struct MotionValues {
    var rotationX: Double = 0.0
    var rotationY: Double = 0.0
    var rotationZ: Double = 0.0
    var pitch: Double = 0.0
    var roll: Double = 0.0
    var yaw: Double = 0.0
}


class MotionManager: ObservableObject {

    @Published var motionValues = MotionValues()

    private let manager = CMMotionManager()

    func startMotionUpdates() {
        manager.deviceMotionUpdateInterval = 1.0
        manager.startDeviceMotionUpdates(to: .main) { (data, error) in

            guard let data = data, error == nil else {
                print(error!)
                return
            }

            self.motionValues.rotationX = data.rotationRate.x
            self.motionValues.rotationY = data.rotationRate.y
            self.motionValues.rotationZ = data.rotationRate.z

            self.motionValues.pitch = data.attitude.pitch
            self.motionValues.roll = data.attitude.roll
            self.motionValues.yaw = data.attitude.yaw
        }
    }

    func stopMotionUpdates() {
        manager.stopDeviceMotionUpdates()
        resetAllMotionData()
    }

    func resetAllMotionData() {
        self.motionValues.rotationX = 0.0
        self.motionValues.rotationY = 0.0
        self.motionValues.rotationZ = 0.0
        self.motionValues.pitch = 0.0
        self.motionValues.roll = 0.0
        self.motionValues.yaw = 0.0
    }
}

My HealthKitManager Class:

class HealthKitManager: ObservableObject {

    private var healthStore = HKHealthStore()
    private var heartRateQuantity = HKUnit(from: "count/min")
    private var activeQueries = [HKQuery]()

    @Published var heartRateValue: Double  = 0.0

    func autorizeHealthKit() {

        let heartRate = HKObjectType.quantityType(forIdentifier: .heartRate)!
        let heartRateVariability = HKObjectType.quantityType(forIdentifier: .heartRateVariabilitySDNN)!

        let HKreadTypes: Set = [heartRate, heartRateVariability]

        healthStore.requestAuthorization(toShare: nil, read: HKreadTypes) { (success, error) in
            if let error = error {
                print("Error requesting health kit authorization: \(error)")
            }
        }
    }

    func fetchHeartRateData(quantityTypeIdentifier: HKQuantityTypeIdentifier ) {

        let devicePredicate = HKQuery.predicateForObjects(from: [HKDevice.local()])
        let updateHandler: (HKAnchoredObjectQuery, [HKSample]?, [HKDeletedObject]?, HKQueryAnchor?, Error?) -> Void = {
        query, samples, deletedObjects, queryAnchor, error in
            guard let samples = samples as? [HKQuantitySample] else {
                return
            }
            self.process(samples, type: quantityTypeIdentifier)
        }
        let query = HKAnchoredObjectQuery(type: HKObjectType.quantityType(forIdentifier: quantityTypeIdentifier)!, predicate: devicePredicate, anchor: nil, limit: HKObjectQueryNoLimit, resultsHandler: updateHandler)
        query.updateHandler = updateHandler
        healthStore.execute(query)
        activeQueries.append(query)
    }

    private func process(_ samples: [HKQuantitySample], type: HKQuantityTypeIdentifier) {
        for sample in samples {
            if type == .heartRate {
                DispatchQueue.main.async {
                    self.heartRateValue = sample.quantity.doubleValue(for: self.heartRateQuantity)
                }
            }
        }
    }

    func stopFetchingHeartRateData() {
        activeQueries.forEach { healthStore.stop($0) }
        activeQueries.removeAll()
        DispatchQueue.main.async {
            self.heartRateValue = 0.0
        }

    }  
}

I started with creating a combinedViewModel but I'm stuck here and don't know if this is the way to go: 

class CombinedViewModel: ObservableObject {

    @Published var motionManager: MotionManager = MotionManager()
    @Published var healthManager: HealthKitManager = HealthKitManager()

    var anyCancellable: AnyCancellable?

    init() {
        anyCancellable = Publishers
            .CombineLatest(motionManager.$motionValues,healthManager.$heartRateValue)
            .sink(receiveValue: {
                // Do something
            }
        })
    }
}

Where do I need to focus ? Do I need to learn the combine framework completely to write my own publishers and subscribers, or is there something available with @Published that can do the job ? Or do I need to go for another approach with my CombinedViewModel?

added contentView for reference:

struct ContentView: View {

    @State var isActive: Bool = false

    private var motion = MotionManager()
    private var health = HealthKitManager()

    @ObservedObject var combinedViewModel = CombinedViewModel(managerOne: motion, managerTwo: health)

    private var motionValues: MotionValues {
        return combinedViewModel.combinedValues.0
    }

    private var heartRateValue: Double {
        return combinedViewModel.combinedValues.1
    }


    var body: some View {
        ScrollView {
            VStack(alignment: .leading) {
                Indicator(title: "X:", value: motionValues.rotationX)
                Indicator(title: "Y:", value: motionValues.rotationY)
                Indicator(title: "Z:", value: motionValues.rotationZ)
                Divider()
                Indicator(title: "Pitch:", value: motionValues.pitch)
                Indicator(title: "Roll:", value: motionValues.roll)
                Indicator(title: "Yaw:", value: motionValues.yaw)
                Divider()
                Indicator(title: "HR:", value: heartRateValue)
            }
            .padding(.horizontal, 10)
            Button(action: {
                self.isActive.toggle()
                self.isActive ? self.start() : self.stop()
            }) {
                Text(isActive ? "Stop" : "Start")
            }
            .background(isActive ? Color.green : Color.blue)
            .cornerRadius(10)
            .padding(.horizontal, 5)
        }.onAppear {
            self.health.autorizeHealthKit()
        }
    }

    private func start() {
        self.motion.startMotionUpdates()
        self.health.fetchHeartRateData(quantityTypeIdentifier: .heartRate)
    }

    private func stop() {
        self.motion.stopMotionUpdates()
        self.health.stopFetchingHeartRateData()
    }

}

Upvotes: 0

Views: 775

Answers (1)

donnywals
donnywals

Reputation: 7591

You can create a new publisher (I would recommend an AnyPublisher) in your CombinedViewModel that combines the output from both. Here's a simplified version of your code with a CombinedViewModel:

class ManagerOne {
  @Published var someValue = "Some Value"
}

class ManagerTwo {
  @Published var otherValue = "Other Value"
}

class CombinedViewModel {
  var combinedPublisher: AnyPublisher<(String, String), Never>

  init(managerOne: ManagerOne, managerTwo: ManagerTwo) {
    combinedPublisher = managerOne.$someValue
      .combineLatest(managerTwo.$otherValue)
      .eraseToAnyPublisher()
  }
}

If you need CombinedViewModel to be an observed object you would adapt the code to be more like this:

class CombinedViewModel: ObservableObject {
  @Published var combinedValue: (String, String) = ("", "")

  var cancellables = Set<AnyCancellable>()

  init(managerOne: ManagerOne, managerTwo: ManagerTwo) {
    managerOne.$someValue
      .combineLatest(managerTwo.$otherValue)
      .sink(receiveValue: { [weak self] combined  in
        self?.combinedValue = combined
      })
      .store(in: &cancellables)
  }
}

A side note about this:

@Published var motionManager: MotionManager = MotionManager()
@Published var healthManager: HealthKitManager = HealthKitManager()

Since both of these managers are classes, $motionManager and $healthManager will only emit values when you assign a new instance of MotionManager or HealthKitManager to them. Not when a property of either manager changes.

Upvotes: 1

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