延迟后在iOS上执行后台任务

Question

Is it possible to run a background task with a delay of about 5 minutes, with the ability to cancel it if the app comes into foreground before the task is executed?

To explain the context of this, the app I am working on has a fairly lengthy set up time when it's opening up. Ideally it needs to clean up all the resources when going into background, and recreate them from scratch when coming into foreground. This is partly for security, partly to reduce device energy use (network, BLE).

This creates an awkward user experience if the user switches to another app for a brief time and comes back to mine. They are stuck waiting for a few seconds for everything to reinitialize.

As a compromise, I want to add a delay to the clean up procedure, say 5 minutes. So that if the user comes back in less than 5 minutes, everything is still there, available immediately. Otherwise it does take a bit of time to reinitialize. How could I implement it?

Answer 1

In iOS, an app can have up to 3 minutes of background processing time when a user exists the app. So if you are willing to use a 3 minute timer, you could use beginBackgroundTaskWithExpirationHandler: on UIApplication.sharedApplication . The background task could then use dispatch_after with a time of 2 minutes, 55 seconds or something close to 3 minutes and do the cleanup. When the user comes back in the app, if the time hasn't expired, you could set a flag or reset the timer so that the dispatch_after does nothing.