Using startDeviceMotionUpdates under Swift 3

Question

Yes, I have seen a previous question on this, but I still can't get this to work. My previous Swift2 code was...

motionMgr.startDeviceMotionUpdatesToQueue(NSOperationQueue(), withHandler: handleMove)

which called:

func handleMove(motion: CMDeviceMotion?, error: NSError?) {
    ...
}

This has changed under Swift3, and now the startDeviceMotionUpdatesToQueue uses a closure. I can't for the life of me figure out how to call my existing method. I realize the NSError became Error and other minor changes, but the syntax of the call from the closure has me very confused.

Answer 1

This should work for you, there are just a few re-namings in Swift 3.

motionMgr.startDeviceMotionUpdates(to: OperationQueue(), withHandler: handleMove)

func handleMove(motion: CMDeviceMotion?, error: Error?) {
    // ...
}

The handler is of type CMDeviceMotionHandler which is defined as a typealias to a closure:

typealias CMDeviceMotionHandler = (CMDeviceMotion?, Error?) -> Void

We just need to provide a closure (or a function, since a function is a closure), that takes in two parameters (a CMDeviceMotion? and Error?) and returns nothing (Void).

Alternatively, you could provide a closure instead of a function like so:

motionMgr.startDeviceMotionUpdates(to: OperationQueue(), withHandler: { deviceMotion, error in
    // ...
})

or use the new trailing closure syntax:

motionMgr.startDeviceMotionUpdates(to: OperationQueue()) { deviceMotion, error in
    // ...
}