Multiple File Upload using uploadTaskWithRequest fromFile in background - ios

Question

I am trying to upload multiple images using NSURLSession .It works fine when application is running in foreground.When application enter background,uploading process stop after uploading current task.I would like to upload all the files when application is in background. Any help would be greatly appreciated. Here is my code.
//background task configuration
-(void) uploadOneByOne:(NSString *)individualpath{
NSMutableURLRequest *request=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:mutableUrlString]];
NSString *requestURL = [NSString stringWithFormat:#"http://myservice/Service.svc/UploadOrdersToDrive?orderFolder=%#",OrderFolderID];
NSMutableURLRequest *request=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:requestURL]];
[request setHTTPMethod:#"POST"];
NSURL *filePath =[NSURL fileURLWithPath:individualpath];
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfiguration:kSessionIdentifier];
defaultSession= [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
NSURLSessionUploadTask *uploadTask =
[defaultSession uploadTaskWithRequest:request
fromFile:filePath];
[uploadTask resume];
}
NSURLSession Delegate
receive first request response
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data
{
NSString * str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(#"Received String %#",str);
NSDictionary *jsonResponseData = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
//FolderID to create next image in same folder.
OrderFolderID =[jsonResponseData
objectForKey:#"OrderFolderID"];
}
create next request
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
if(error == nil)
{
//Remove DetailFist
[orderDetailarray removeObjectAtIndex:0];
if (orderDetailarray.count >0){
ChosenImages *item = [orderDetailarray objectAtIndex:0];
[self uploadOneByOne:item.path ];
}
}
//Update progress bar
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didSendBodyData:(int64_t)bytesSent
totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend{
//update progress bar
}

Answer 1

Probably you didn't wait enough for next task to start. Depending from different things like WiFi and battery status, user activity etc. your next task queued in background could start in few minutes.. or few hours.
Btw I don't see code related with completionHandler implementation.
Do not forgot to implement
- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler
in the App delegate and appropriate session delegate.