In the class method case, the scope of your `manager` object is local the the
class method and it is deallocated immediately as function returns (before the
closure gets a chance to be called).
> On Jul 24, 2017, at 12:22 PM, Nate Birkholz via swift-users
> <swift-users@swift.org> wrote:
>
> If I use these two classes:
>
> class MotionManager {
>
> class func doTheThing(completionHandler: @escaping (CMDeviceMotion?)->()
> ) {
> print("in")
> let manager = CMMotionManager()
> manager.deviceMotionUpdateInterval = 0.01
>
> manager.startDeviceMotionUpdates(to: .main) { (motion, error) in
> print("out")
> completionHandler(motion)
> }
> }
> }
>
> class OtherManager {
> let manager: CMMotionManager
>
> init() {
> manager = CMMotionManager()
> manager.deviceMotionUpdateInterval = 0.01
> }
>
> func doTheThing(completionHandler: @escaping (CMDeviceMotion?)->() ) {
> print("in 2")
> manager.startDeviceMotionUpdates(to: .main) { (motion , error) in
> completionHandler(motion)
> print("out 2")
> self.manager.stopDeviceMotionUpdates()
> }
> }
> }
>
> let other = OtherManager()
>
> other.doTheThing { (motion) in
> print(motion)
> }
>
> MotionManager.doTheThing { (motion) in
> print(motion)
> }
>
> The class method on MotionManager prints "in" but never prints "out". The
> instance method version on. OtherManager works just fine, printing "in 2" and
> "out 2". Clearly the CMMotionManager doesn't survive long enough to finish
> its call, but I would have thought it would.
>
> Is this a bug? Or am I just misunderstanding how the class method should work?
>
> --
> Nate Birkholz
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> swift-users@swift.org
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