Bluetooth Low Energy in the Background - iOS8 Followup

I posted about the results of some experiments I had done using the iOS background modes for Bluetooth. At the time I hadn't updated any devices to iOS8 (and they would have been betas anyway). This is a quick update to confirm that there are no changes in these areas that I can see in iOS8.

If you do know of any iOS8 changes or workarounds to the issues described please let me know

Basic Findings (repeated from earlier article)

  1. Apps on BLE capable iOS devices can be woken from the background when a device with the correct UUID is detected even when they have been completely removed from memory due to other apps needing the memory.
  2. This background listening/advertising state is stopped if the app is deliberately closed by the user swiping it up from the task switcher.
  3. The background listening/advertising state is stopped if the device is switched off or runs out of battery. It isn't restarted until the App is run again. (I haven't actually retested running out of battery but am guessing it is the same as manually powering off I will try to test again when the battery on something is getting low)


Please see the previous article for discussion of the impact on on app design and some potential workarounds.

London Swift Presentation - Swifter Swift

This is the Swifter Swift presentation I gave at the London Swift Meetup in Clapham today (15th September 2014). Apologies for the stock photos/standard template, I focussed on the content.

I also showed the optimisation levels as described in this blog post.

Things I Forgot To Mention

Use constants - declare with let unless avoidable, allows extra optimisation. Test before changing to mutable state within a function for performance reasons.

Currently the optimiser can do better within a particular file although this will be fixed at some point.

Github Repos

https://github.com/josephlord/GrayScott - Optimised version of Simon Gladwell's Cellular Automata project.

Async.legacy - My iOS7 / OS X 10.9 compatible fork.

Async - Original by Tobias Duemunk




Async.legacy - Swift wrapper for Grand Central Dispatch (iOS7 and OS X 10.9 compatible)

While GCD is a fairly simple API enabling blocks to be dispatched asynchronously on different threads or on particular queues that doesn't mean that the API can't be cleaned up a little to make it really nice to use with Swift.

Tobias Due Monk released the Async library that does just that. I saw the announcement probably on iOSDevWeekly and I liked what I saw except there was one fatal issue for me in that the library required iOS 8 or OS X 10.10 and I haven't updated my devices yet let alone moved my target up to that version yet. I actually just left it and ignored it but having done the optimisation of the GrayScott code presented at the last Swift London meetup I felt comfortable enough with GCD that I could implement most of the fuctionality to work with iOS 7 (and OS X 10.9 Mavericks but just take that as read every time I mention iOS 7 in this article). The result was Async.Legacy

How to Use Async (or Async.legacy)

All you need to do is to drop in the Async.swift (or AsyncLegacy.swift if you are using iOS7) into your project and then you can call the methods. There is full API documentation in the Readme files and that are easily viewable on the Github pages but essentially what Async allows you to do is chain a series of Asyncronous calls rather than to nest them. The result looks like:

Instead of having to nest the calls like this: