Core Motion Swift Closure issue - ios

Question

I'm trying to convert an old game application built in obj-c to the new swift code. i'm having some issues understanding swift closures and how to use them for example in the"startAccelerometerUpdatesToQueue" method.
i have initialized the motion manager in this way
motionManager!.accelerometerUpdateInterval = (1/40)
then in the viewdidload of my view controller
var queue:NSOperationQueue
motionManager?.startAccelerometerUpdatesToQueue(queue, withHandler: {(accelerometerData : CMAccelerometerData, error : NSError) in
})
the "startAccelerometerUpdatesToQueue" is giving me an error and i'm pretty sure i didn't understand the correct closure syntax.
Any ideas?

Answer 1

Actually, you just got the signature wrong – the arguments to your closure need to be optionals (since they are passed from Objective-C, they could be nil). Because of that, the arguments you provide don't match an existing method signature, and because of that you get an error.
Take a look at the iOS 8 API docs, they also provide Swift signatures:
func startAccelerometerUpdatesToQueue(_ queue: NSOperationQueue!,
withHandler handler: CMAccelerometerHandler!)
and CMAccelerometerHandler is defined as
typealias CMAccelerometerHandler = (CMAccelerometerData!, NSError!) -> Void
Thus, your call should be:
motionManager?.startAccelerometerUpdatesToQueue(queue, withHandler: {(accelerometerData : CMAccelerometerData!, error : NSError!) in
})
And as with any function/method that takes a closure as it's last argument, you can leave it out of the argument list and write it after the call (trailing closure syntax – this example also leaves out the types, as they can be inferred, but that is optional):
motionManager?.startAccelerometerUpdatesToQueue(queue) { accelerometerData, error in
}

Answer 2

CMMotionManager
object is the gateway to the motion services provided by iOS. These services provide an app with accelerometer data, rotation-rate data, magnetometer data, and other device-motion data such as attitude. These types of data originate with a device’s accelerometers and (on some models) its magnetometer and gyroscope.
Handling Motion Updates at Specified Intervals
To receive motion data at specific intervals, the app calls a “start” method that takes an operation queue (instance of NSOperationQueue) and a block handler of a specific type for processing those updates. The motion data is passed into the block handler. The frequency of updates is determined by the value of an “interval” property.
Accelerometer.
Set the accelerometerUpdateInterval property to specify an update interval. Call the startAccelerometerUpdatesToQueue:withHandler: method, passing in a block of type CMAccelerometerHandler. Accelerometer data is passed into the block as CMAccelerometerData objects.
Gyroscope.
Magnetometer.
Device motion.
The interval, in seconds, for providing accelerometer updates to the block handler.
Declaration
SWIFT
var accelerometerUpdateInterval: NSTimeInterval
Discussion
The system supplies accelerometer updates to the block handler specified in startAccelerometerUpdatesToQueue:withHandler: at regular intervals determined by the value of this property.
The interval units are in seconds. The value of this property is capped to minimum and maximum values; the maximum value is determined by the maximum frequency supported by the hardware. If your app is sensitive to the intervals of acceleration data, it should always check the timestamps of the delivered CMAccelerometerData instances to determine the true update interval.
Availability
Available in iOS 4.0 and later.

Answer 3

import UIKit
import CoreMotion
class ViewController: UIViewController {
let motionManager = CMMotionManager()
var timer: Timer!
override func viewDidLoad() {
super.viewDidLoad()
motionManager.startAccelerometerUpdates()
motionManager.startGyroUpdates()
motionManager.startMagnetometerUpdates()
motionManager.startDeviceMotionUpdates()
timer = Timer.scheduledTimer(timeInterval: 3.0, target: self, selector: #selector(ViewController.update), userInfo: nil, repeats: true)
}
#objc func update() {
if let accelerometerData = motionManager.accelerometerData {
print(accelerometerData)
}
if let gyroData = motionManager.gyroData {
print(gyroData)
}
if let magnetometerData = motionManager.magnetometerData {
print(magnetometerData)
}
if let deviceMotion = motionManager.deviceMotion {
print(deviceMotion)
}
}
}