Fetching data using NsoperationQueue in sleep mode - ios

Question

I have added data fetching operations to NSOperationQueue .During the process, I just put the device to sleep mode and the process gets stopped. I surfed stack overflow an get some basic ideas.I need help to continue my fetching process without any interruption when device moves to sleep mode.Help appreciated !!
NSManagedObjectContext *managedObjectContext=((AppDelegate *)[[UIApplication sharedApplication] delegate]).managedObjectContext;
NSOperationQueue *downLoadQueue=((AppDelegate *)[[UIApplication sharedApplication] delegate]).downloadqueue;
//Fetch operation
if([fetchqueue count]>0)
{
Queue *queue=[fetchqueue objectAtIndex:0];
queue.status=#"INP";
[managedObjectContext performBlockAndWait:^{
NSError * error = nil;
if (![managedObjectContext save:&error]){
NSLog(#"Unresolved error while loading3");
}
}];
DownloadOperation *downloadOp=[[DownloadOperation alloc]init];
downloadOp.queue=queue;
[downLoadQueue addOperation:downloadOp];
}
}
The downLoadQueue started its execution. It is fetching data from server meanwhile the device goes to sleep and the execution stops. I don't know how to continue in this block applicationDidEnterBackground. How can I get my lengthy downloading process during sleep mode?
Also tried this one..But the operation was not resumed.
//code follows
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSOperationQueue *downLoadQueue;
downLoadQueue=((AppDelegate *)[[UIApplication sharedApplication] delegate]).downloadqueue;
[downLoadQueue waitUntilAllOperationsAreFinished];
});
}
Please suggest any ideas.

Answer 1

I think the only way to do this is background task. Take a look at apple docs about this. There are also a lot of answers on stackowerflow how to implemet such feature.
I think in your case you can try next code to execute NSOperations a in backgraund task:
- (void)applicationDidEnterBackground:(UIApplication *)application
{
bgTask = [application beginBackgroundTaskWithName:#"MyTask" expirationHandler:^{
// Clean up any unfinished task business by marking where you
// stopped or ending the task outright.
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
// Start the long-running task and return immediately.
//Start your NSOperationQueue if it's not executing
//Lock current thread while operations are executing
[queue waitUntilAllOperationsAreFinished];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Do the work associated with the task, preferably in chunks.
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
});
}