How to sync async with server once pressed the home button? - ios

Question

- (void)applicationDidEnterBackground:(UIApplication *)application
{
[_dataStore saveChanges];
[_sync syncWithServerWithDate:[NSDate dateWithTimeIntervalSince1970:timestamp]];
}
-(void)syncWithServerWithDate:(NSDate *)date
{
void(^postCompletionBlock)(FTjsonEvents *obj, NSError *error) = ^(FTjsonEvents *serverEvents, NSError *error) {
...
NSLog(#"Post Completion block finished!");
};
void(^completionBlock)(FTjsonEvents *obj, NSError *error) = ^(FTjsonEvents *serverEvents, NSError *error) {
....
NSLog(#"Fetch finished!");
[self postRecordsSinceLastServerSyncTimestamp:[date timeIntervalSince1970] WithCompletion:postCompletionBlock];
};
NSLog(#"Syncing data...");
[self fetchRecordsByDate:date WithCompletion:completionBlock];
}
I would like to sync with the server to fetch and post the latest data to.
Since this is happening via async completion blocks, it seems that my classes get garbage collected once I press home button. The sync never reaches the server.
However the local coredata is easily saved when doing this: [_dataStore saveChanges];
Is there a way to keep the async sync alive in the background until its completed?

Answer 1

Your implementation of applicationDidEnterBackground: has approximately five seconds to perform any tasks and return. If you need additional time to perform any final tasks, you can request additional execution time from the system by calling beginBackgroundTaskWithExpirationHandler:. In practice, you should return from applicationDidEnterBackground: as quickly as possible. If the method does not return before time runs out your app is terminated and purged from memory.
You should perform any tasks relating to adjusting your user interface before this method exits but other tasks (such as saving state) should be moved to a concurrent dispatch queue or secondary thread as needed. Because it's likely any background tasks you start in applicationDidEnterBackground: will not run until after that method exits, you should request additional background execution time before starting those tasks. In other words, first call beginBackgroundTaskWithExpirationHandler: and then run the task on a dispatch queue or secondary thread.
Here's an example implementation:
#interface XXAppDelegate (BackgroundStuff)
#property (nonatomic, assign) UIBackgroundTaskIdentifier backgroundTask;
#end
#implementation
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Request additional background time.
self.backgroundTask = [application beginBackgroundTaskWithExpirationHandler:^{
[application endBackgroundTask:self.backgroundTask];
}];
// Start background task.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//Background code goes here
//Cleanup background task id
[application endBackgroundTask:self.backgroundTask];
self.backgroundTask = UIBackgroundTaskInvalid;
});
}
#end