iOS how to execute a task with beginBackgroundTaskWithExpirationHandler - ios

Question

I am trying to do two things for a simple test app.
I am stuck at trying to learn how to use beginBackgroundTaskWithExpirationHandler
I want to execute a backgroundTask when the user presses the home button (nothing fancy). In 9 minutes, I'd like to alert the user that the time is about to expire (if possible) and allow the user to switch back into the app to renew the 10 minutes.
I don't need backward compatibility with iOS 3, or 4.

Answer 1

If you want your code to continue in the background, then you'll need to wrap it in a background task. It's also very important that you call endBackgroundTask when you're finished - otherwise the app will be killed after it's allotted time has expired
- (IBAction) buttonPressed: (id) sender
[self beingBackgroundUpdateTask];
// Do your long running background thing here
[self endBackgroundUpdateTask];
});
}
- (void) beingBackgroundUpdateTask
{
self.backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[self endBackgroundUpdateTask];
}];
}
- (void) endBackgroundUpdateTask
{
[[UIApplication sharedApplication] endBackgroundTask: self.backgroundUpdateTask];
self.backgroundUpdateTask = UIBackgroundTaskInvalid;
}

Answer 2

Put the code in the applicationDidEnterBackground function in your UIApplicationDelegate. You will need to set up a UILocalNotification and schedule it. You should also probably disable it in applicationWillEnterForeground so it doesn't fire off the user goes back to the app before it expires.
- (void)applicationDidEnterBackground:(UIApplication *)application
{
UILocalNotification *timerNotification = [[UILocalNotification alloc] init];
//set up notification with proper time and attributes
[[UIApplication sharedApplication] scheduleLocalNotification:timerNotification];
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
[[UIApplication sharedApplication] cancelAllLocalNotifications];
}
The cancelling code I gave there will actually cancel all notifications. If you have multiple notifications and only want to cancel a specific one, you should give the userInfo property of your notification a key/value when you set it up. Then, when the application enters the foreground, get the list of all active notifications by doing
NSArray *notifications = [[UIApplication sharedApplication] scheduledLocalNotifications];
and loop through them, checking userInfo until you get to the one you want and then just cancelling that one with
[[UIApplication sharedApplication] cancelLocalNotification:whateverNotification];