Apple Swift - Unable to retrieve data from CMPedometer's handler - ios

Question

I am trying out Swift with some of the new iOS 8 API's and have tried the best part of the day to get the CMPedometer queryPedometerDataFromDate API to return any data within the handler. I believe its an error on my part, getting a little confused with the syntax.
Here is my code, with comments on what prints out:
var ped = CMPedometer()
var stepsTaken = NSNumber(int: 0)
println(dateNow) // 2014-06-07 21:23:55 +0000
println(dateMidnight) // 2014-06-07 00:00:00 +0000
ped.queryPedometerDataFromDate(dateMidnight, toDate: dateNow, withHandler:{
data, error in
println("Test1") // Does not print
println(error) // Does not print
stepsTaken = data.numberOfSteps
})
println("My Int Value \(stepsTaken)") // My Int Value 0

Answer 1

It works for me with CMPedometer queryPedometerDataFromDate, if i define the CMPedometer as a class wide constant:
let pedometer = CMPedometer()
and then in a func i'm using:
self.pedometer.queryPedometerDataFromDate(today, toDate: now, withHandler: ...

Answer 2

A code sample from Hipster.
import CoreMotion
let lengthFormatter = NSLengthFormatter()
let pedometer = CMPedometer()
pedometer.startPedometerUpdatesFromDate(NSDate(), withHandler: { data, error in
if !error {
println("Steps Taken: \(data.numberOfSteps)")
var distance = data.distance.doubleValue
println("Distance: \(lengthFormatter.stringFromMeters(distance))")
var time = data.endDate.timeIntervalSinceDate(data.startDate)
var speed = distance / time
println("Speed: \(lengthFormatter.stringFromMeters(speed)) / s")
}
})

Answer 3

After many hours playing around with the syntax, thinking I have made a rookie error, I tried alternative API's and found that the following works to grab pedometer data:
var ped2 = CMStepCounter()
ped2.queryStepCountStartingFrom(dateMidnight, to: dateNow, toQueue: NSOperationQueue(), withHandler:{data, error in
println("Test 2") // "Test 2"
println(data) // 491 (I really should go for a walk!)
println(error) // nil
})
I will file a radar with Apple as it looks like a bug in the new API. Also the CMStepCounter class is due to be deprecated for CMPedometer. From CMStepCounter.h:
NS_CLASS_DEPRECATED_IOS(7_0,8_0,"Use CMPedometer instead")

Answer 4

You're querying the data, which goes onto another thread. The execution continues after your call, and your NSNumber is still at 0. By the time you've come back you've printed the message a long time ago, and have no way of recovering the stepsTaken.

Answer 5

You need to keep a reference to your ped variable. Something like:
self.ped = CMPedometer();
Currently your ped variable is going out of scope before the handler is even called.