---
title: "startMirroringToCompanionDevice(completion:)"
framework: healthkit
role: symbol
role_heading: Instance Method
path: "healthkit/hkworkoutsession/startmirroringtocompaniondevice(completion:)"
---

# startMirroringToCompanionDevice(completion:)

Starts mirroring the workout session to the companion iOS device.

## Declaration

```swift
func startMirroringToCompanionDevice(completion: @escaping @Sendable (Bool, (any Error)?) -> Void)
```

```swift
func startMirroringToCompanionDevice() async throws
```

## Parameters

- `completion`: A block that the system calls when the start request is complete. The system sets the following parameters:

## Discussion

Discussion Call this method in your watchOS app to start a mirrored workout session on the companion iOS app. If your iOS app isn’t running, the system launches it in the background. The iOS companion app must assign a completion handler to its HealthKit Store’s workoutSessionMirroringStartHandler property to process the incoming session. important: This method fails if you call it on a workout session that ended. let configuration = HKWorkoutConfiguration() configuration.activityType = .running configuration.locationType = .outdoor

let session: HKWorkoutSession do {     session = try HKWorkoutSession(healthStore: store,                                    configuration: configuration) } catch {     // Handle failure here.     fatalError("*** An error occurred: \(error.localizedDescription) ***") }

let builder = session.associatedWorkoutBuilder()

let source = HKLiveWorkoutDataSource(healthStore: store,                                      workoutConfiguration: configuration)

source.enableCollection(for: HKQuantityType(.stepCount), predicate: nil) builder.dataSource = source

session.delegate = self builder.delegate = self

self.session = session self.builder = builder

let start = Date()

// Start the mirrored session on the companion iPhone. do {     try await session.startMirroringToCompanionDevice() } catch {     fatalError("*** Unable to start the mirrored workout: \(error.localizedDescription) ***") }

// Start the workout session. session.startActivity(with: start)

do {     try await builder.beginCollection(at: start) } catch {     fatalError("*** An error occurred while starting the workout: \(error.localizedDescription) ***") }

## See Also

### Working with remote workout sessions

- [stopMirroringToCompanionDevice(completion:)](healthkit/hkworkoutsession/stopmirroringtocompaniondevice(completion:).md)
- [sendToRemoteWorkoutSession(data:completion:)](healthkit/hkworkoutsession/sendtoremoteworkoutsession(data:completion:).md)