In IOS 11, DeviceMotion in background stopped working

Question

My app reports and records location, altitude, rotation and accelerometer data (DeviceMotion) while in the background. This works fine on ios 10.3.3. On IOS 11, I no longer

Answer 1

Also came across this problem.

Our solution was to ensure we have another background mode enabled and running (in our case location updates + audio) and restart core motion updates when switching background/foreground.

Code sample:

import UIKit
import CoreMotion

final class MotionDetector {
    private let motionManager = CMMotionManager()
    private let opQueue: OperationQueue = {
        let o = OperationQueue()
        o.name = "core-motion-updates"
        return o
    }()

    private var shouldRestartMotionUpdates = false

    init() {
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(appDidEnterBackground),
                                               name: .UIApplicationDidEnterBackground,
                                               object: nil)
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(appDidBecomeActive),
                                               name: .UIApplicationDidBecomeActive,
                                               object: nil)
    }

    deinit {
        NotificationCenter.default.removeObserver(self,
                                                  name: .UIApplicationDidEnterBackground,
                                                  object: nil)
        NotificationCenter.default.removeObserver(self,
                                                  name: .UIApplicationDidBecomeActive,
                                                  object: nil)
    }

    func start() {
        self.shouldRestartMotionUpdates = true
        self.restartMotionUpdates()
    }

    func stop() {
        self.shouldRestartMotionUpdates = false
        self.motionManager.stopDeviceMotionUpdates()
    }

    @objc private func appDidEnterBackground() {
        self.restartMotionUpdates()
    }

    @objc private func appDidBecomeActive() {
        self.restartMotionUpdates()
    }

    private func restartMotionUpdates() {
        guard self.shouldRestartMotionUpdates else { return }

        self.motionManager.stopDeviceMotionUpdates()
        self.motionManager.startDeviceMotionUpdates(using: .xArbitraryZVertical, to: self.opQueue) { deviceMotion, error in
            guard let deviceMotion = deviceMotion else { return }
            print(deviceMotion)
        }
    }
}