IOS - Executing a Finite-Length Task in the Background

Question

I am writing an iOS app which sync data. I need sync service to run when app is in background as well. So I've written this piece of code in the place where I am uploading data.

 - (void)startAsyncUpload {
UIApplication *thisApplication = [UIApplication sharedApplication];

if([thisApplication respondsToSelector:@selector(beginBackgroundTaskWithExpirationHandler:)]) {
    bgTaskIdentifier_ = [thisApplication beginBackgroundTaskWithExpirationHandler:^(void)
                         {
                             [thisApplication endBackgroundTask:bgTaskIdentifier_];
                             bgTaskIdentifier_ = UIBackgroundTaskInvalid;
                         }];
}

[self multipartUpload];}

It works fine and run in background. But I've a problem here. I was uploading a video file and when my background time expired the handler was called and it ended the task. Now when I came to foreground again uploading resumed, fine. But now when I went to background again it's not resuming the background task.

I know why, basically because I ended the task before. But is there any way to resume the task again, something like registering the task again for background running?

Answer 1

Are you sure you are calling beginBackgroundTaskWithExpirationHandler: for the second time?

Create one ivar/property for bgTaskIdentifier and one for a BOOL isUploading. Then you could write a method like this

- (void)resumeOrStartAsyncLoad 
{
   if(!self.isUploading) 
   {
      [self multipartUpload];
      self.isUploading = TRUE;
   }

   if(self.isUploading && self.bgTaskIdentifier == UIBackgroundTaskInvalid) 
   {
      UIApplication *thisApplication = [UIApplication sharedApplication];
      self.bgTaskIdentifier = [thisApplication beginBackgroundTaskWithExpirationHandler:^(void) {
         [thisApplication endBackgroundTask:bgTaskIdentifier_];
         bgTaskIdentifier_ = UIBackgroundTaskInvalid;
      }];
   }
}