We covered retrieving step counts for a user using CMPedometer back in Bite #41. Today we're going to look at some interesting additions to CMPedometer in iOS 9. They involve determining at what rate the user is moving, as well as what kind of "cadence" their movement has. Let's dive in:

First let's look at what pace and cadence are referring to. In Core Motion's world. "Pace" represents the amount of time (in seconds) it takes a user to go one meter. "Cadence" on the other hand describes the number of steps the user is current taking each second.

Now that we know what we're working with, let's wire up a simple view controller to display our current pace and cadence. We'll start by adding two functions to start and stop pedometer updates. We'll star them in viewWillAppear: and stop them in viewWillDisappear:.

We'll make sure cadence and pace are supported on this device then start updates just like we did in Bite #41. Since we're looking for real-time data instead of historical data, we'll pass in a new NSDate (essentially "now"). Then, we'll make sure we've gotten back valid data and set the text of our labels. To test it out, we can install the app on our phone, and walk

around a bit. Success! It's fun to imagine the possibilities here: A music app that plays different songs depending on how fast a user is jogging, or an app that estimates your arrival time based on your current pace, neat!

func startUpdatingPaceAndCadence() {
  guard CMPedometer.isCadenceAvailable() && CMPedometer.isPaceAvailable() else {
    showPaceAndCadenceUnsupportedAlert(); return
  }

  pedometer.startPedometerUpdatesFromDate(NSDate()) { data, error in
    guard let data = data where error == nil else {
      self.showErrorRetrievingDataAlert()
      return
    }

    if let pace = data.currentPace, let cadence = data.currentCadence {
      self.paceLabel.text = pace.stringValue
      self.cadenceLabel.text = cadence.stringValue
    }
  }
}

Download the example we built here at j.mp/bite117 to try it out on your own device.

CMPedometer is part of the Core Motion framework. One of the features it provides is the ability to retrieve the number of steps a user has taken during a given time period. Let’s take a look at how to do it:

import Timepiece

let pedometer = CMPedometer()

if CMPedometer.isStepCountingAvailable() {
    // NSDate.beginningOfDay comes from the Timepiece library

    pedometer.queryPedometerDataFromDate(NSDate.beginningOfDay, toDate: NSDate()) { data, error in
      guard let data = data else { return }

      print("The user has taken \(data.numberOfSteps) so far today, that's \(data.distance) meters!")
    }
}

We first import the Timepiece library (covered in Bite #3) and create a pedometer object. Then we check if the device supports step counting, and then we ask for the pedometer data since the beginning of today. The call hands back a CMPedometerData object which has properties representing the number of steps taken and the distance traveled.