Whilst using the public version of iOS 5.1 I’ve noticed an interesting bug with one of my apps. WallaBee uses Location Services but as all good apps should it makes a point of stopping location monitoring after a certain amount of inactivity (to save battery) and also when the app goes into the background. Location monitoring starts up again as soon as you go back to the foreground or navigate to a page that will require more precise location monitoring.
On iOS 5.0.*, closing the app would lead to the Location Services indicator disappearing immediately. On iOS 5.1, Location Services stays active for ~10 seconds after it’s been told explicitly to stop monitoring. Initially I thought this might be a problem with the code I’d written but, after some testing on multiple devices and with multiple apps, it turns out this is an issue that affects all location based apps on iOS 5.1.
It isn’t really a big issue but it is fairly annoying, particularly as some apps do keep monitoring your location in the background so you end up trying to work out what is still running only to realise it’s the OS not giving up when it should do. It’s particularly annoying as an app developer - v1.0.3 of WallaBee came out on the day iOS 5.1 was released and I’ve now had 3 enquries as to why Location Services is less efficient in the new version (whereas it’s actually much more efficient in the app).
In terms of why iOS 5.1 is doing this, I can only assume that Location Services is told to turn off after the full amount of background task allowance has been used. If an app doesn’t ask to run in the background, it has around 10 seconds after being closed to do any tidying up (i.e. saving documents, closing network connections) before the OS forcably terminates it. This seems to be the case with Location Services as if you close the app and then force quit, the service is stopped (suggesting ownership is with the app, not the OS).
It’s probably an oversight on Apple’s part (as I can’t think of a good reason why this would be built-in) but I thought I’d put up a post on the issue for any other developers who run into the problem and for anyone using my apps and wondering why Location Services is still active once the app is closed.