ios - Crash with NSURLSessionUploadTask when trying to upload in background -

in app try upload data server when app enters background. code using:

session

self.session = [self backgroundsession]; 

this how session set up

- (nsurlsession *)backgroundsession {     static nsurlsession *session = nil;     static dispatch_once_t oncetoken;     dispatch_once(&oncetoken, ^{         nsurlsessionconfiguration *configuration = [nsurlsessionconfiguration backgroundsessionconfiguration:@"com.uploadsession"];         configuration.httpmaximumconnectionsperhost = 1;         session = [nsurlsession sessionwithconfiguration:configuration delegate:self delegatequeue:nil];     });     return session; } 

initiate upload

- (void)applicationdidenterbackground:(uiapplication *)application {     [self uploadpossibledrives]; } 

upload

// start uploading remaing gps log in th right order:  nsoperationqueue *queue = [[nsoperationqueue alloc] init]; [queue setmaxconcurrentoperationcount:1];  (int = 0; < arrayofgpslogchunks.count; i++) {      // ensure chunks sent in right order     // add operation block queue:      [queue addoperationwithblock: ^ {          nsdata *requestdata;         nsmutableurlrequest *request;          if (i == 0)         {             nslog(@"initial drive upload %i",id.integervalue);              requestdata = [nsjsonserialization datawithjsonobject:historytoupload options:nsjsonwritingprettyprinted error:nil];             request = [[nsmutableurlrequest alloc] initwithurl:[nsurl urlwithstring:kinitialuploaddriveurl];             [request sethttpmethod:@"post"];             [request setvalue:@"application/json" forhttpheaderfield:@"content-type"];             [request setvalue:[nsstring stringwithformat:@"%d", [requestdata length]] forhttpheaderfield:@"content-length"];          }         else         {             nslog(@"chunk %i",i);              nsmutabledictionary *chunk = [[nsmutabledictionary alloc] init];             [chunk setobject:driveid forkey:@"driveid"];             [chunk setobject:[arrayofgpslogchunks objectatindex:i] forkey:@"gpslog"];              requestdata = [nsjsonserialization datawithjsonobject:chunk options:nsjsonwritingprettyprinted error:nil];             request = [[nsmutableurlrequest alloc] initwithurl:[nsurl urlwithstring:kuploaddriveschunkurl]];             [request sethttpmethod:@"post"];             [request setvalue:@"application/json" forhttpheaderfield:@"content-type"];             [request setvalue:[nsstring stringwithformat:@"%d", [requestdata length]] forhttpheaderfield:@"content-length"];           }          nslog(@"_session: %@",self.session);         nslog(@"request: %@",request);         nslog(@"requestdata: %lu",(unsigned long)requestdata.length);         nslog(@"uploadtask: %@",self.uploadtask);          self.uploadtask = [self.session uploadtaskwithrequest:request fromdata:requestdata];         [self.uploadtask resume];          if (i == arrayofgpslogchunks.count-1)         {             // gps logs uploaded save state 'uploaded server':             nslog(@"finished sending server!");             [self setsenttoserverfordriveid:id];         }      }];  } 

error

now here error get:

i hope can me out. have looked know cant seem figure out ist going wrong. tried uploading without using blocks result same.

any appreciated!

for nsurlsession created backgroundsessionconfiguration, have use uploadtaskwithrequest:fromfile:.

see question: nsurlsession , stream upload in background