10

I'm writing a iOS/Swift application which reads data from a REST service each X minutes and updates the UI accordingly.

Now I would like that when the app is put in the background, a task keeps being invoked at X minutes intervals reading from the REST service and, in case the data just read satisfies a given condition, show a notification prompting the user to bring the app back to the foreground.

In my searches I've read that during applicationDidEnterBackground event, I should start a task with beginBackgroundTaskWithExpirationHandler.

The problem is that, if I've understood correctly, this allows a maximum of 10/15 minutes after which the app is terminated if the task is not stopped with endBackgroundUpdateTask, while I want the task to keep polling the service indefinitely (at least until the user disable it from the app's settings)

My question is:

How is this kind of functionality performed normally? Do some common solutions or best practices exist for the solution of such a problem?

Dan Beaulieu
  • 19,406
  • 19
  • 101
  • 135
chrx
  • 2,169
  • 5
  • 24
  • 45

3 Answers3

6

Use iOS Background Fetch feature where you can specify minimum background fetch interval. But actual interval between successive invocation of your code will be determined by iOS framework. For details checkout this link: http://code.tutsplus.com/tutorials/ios-7-sdk-working-with-background-fetch--mobile-20520

I use this approach in my app and I think it is a preferred way of doing.

Suresh
  • 225
  • 2
  • 7
  • thank you very much, this seems to address exactly the kind of problem I have – chrx Dec 19 '14 at 14:19
  • Even with my screen on it takes several minutes to the next "performFetchWithCompletionHandler" (and I return .newData each time). That kind of sucks. – Makalele Jan 03 '17 at 23:41
1

  1. You can use a local notification that can be presented from the background in case your condition is met.

  2. Correct, iOS will eventually shut down the background process, you can't enforce continuous background activity. Use the backgroundTimeRemaining property to check how much time your application has left and try to handle it as gracefully as possible by calling endBackgroundTask so that iOS does not force kill your app.

As a solution, you could think about using remote notifications with with content-available : YES, which runs the didReceiveRemoteNotification

MarkHim
  • 5,686
  • 5
  • 32
  • 64
  • Thanks for your reply. With remote notifications you mean push notifications, right? The problem is that if I'm not wrong, to implement these I should be able to change things on the server side, while I was looking for a more lightweight solution just allowing to continue the allotted time for the background task indefinitely. For instance, I was now investigating the possibility to have the task run for, say, 1 minute, then terminate the task and immediately run a new one, but I don't know if this is feasible/allowed. – chrx Dec 18 '14 at 15:45
1

Have a look at the Parse.com Their local datastore is an abstraction for what you are trying to acheive. By the way, is it really necessary to refresh in the background. If call is relatively quick, there is no need to refresh until the user open's the app. Background processes like that, using the net can be quite battery consuming when the user are not on a Wifi. So consider the use case carefully!

Lars Christoffersen
  • 1,719
  • 13
  • 24