ios - background request cases a CATransaction error -

i trying download image in background. when trying download it, receive next error:

+[catransaction synchronize] called within transaction

i trying download in cellforrowatindexpath of uitableview. have first encountered such problem. in advance. here code that, located in separate file:

- (id) initwithimageid: (nsstring*) imageid {     self = [super init];      if (self)     {         self.receiveddata = [nsmutabledata data];         self.imageid = imageid;          notedpreferences* np = [notedpreferences sharedpreferences];         nsstring* url = [[np apiurl] stringbyappendingformat: @"/thumbs/%@.jpg", imageid];         nsurl* imageurl = [nsurl urlwithstring: url];          nsmutableurlrequest *therequest = (nsmutableurlrequest*)[nsmutableurlrequest requestwithurl:imageurl cachepolicy:nsurlrequestuseprotocolcachepolicy timeoutinterval:timeout60];         [self basicauthforrequest:therequest withusername:@"app" andpassword:@"123"];         self.theconnection = [[nsurlconnection alloc] initwithrequest:therequest delegate:self];         cfrunlooprun();     }      return self; }  - (void)basicauthforrequest:(nsmutableurlrequest *)request withusername:(nsstring *)username andpassword:(nsstring *)password {     cfstringref usernameref = (__bridge cfstringref)username;     cfstringref passwordref = (__bridge cfstringref)password;      cfhttpmessageref authoriztionmessageref = cfhttpmessagecreaterequest(kcfallocatordefault,    (__bridge cfstringref)[request httpmethod], (__bridge cfurlref)[request url], kcfhttpversion1_1);      cfhttpmessageaddauthentication(authoriztionmessageref, nil, usernameref, passwordref, kcfhttpauthenticationschemebasic, false);      cfstringref authorizationstringref = cfhttpmessagecopyheaderfieldvalue(authoriztionmessageref, cfstr("authorization"));      [request setvalue:(__bridge nsstring *)authorizationstringref forhttpheaderfield:@"authorization"];      cfrelease(authorizationstringref);     cfrelease(authoriztionmessageref); }  - (void)connection: (nsurlconnection *) connection didreceivedata: (nsdata *) data {     [self.receiveddata appenddata: data]; }  - (void)connectiondidfinishloading:(nsurlconnection *)connection {     if (self.receiveddata != nil)     {         uiimage* image = [uiimage imagewithdata: self.receiveddata];          if ([self.delegate respondstoselector:@selector(requesthavefinishedwithimage:imageid:success:)])             [self.delegate requesthavefinishedwithimage:image imageid:self.imageid success: true];     }      cfrunloopstop(cfrunloopgetcurrent()); }  - (void)connection: (nsurlconnection *) connection didfailwitherror: (nserror *) error {     if ([self.delegate respondstoselector:@selector(requesthavefinishedwithimage:imageid:success:)])         [self.delegate requesthavefinishedwithimage:nil imageid:self.imageid success: false];      cfrunloopstop(cfrunloopgetcurrent()); }  - (void) dealloc {     nslog(@"dealloc of downloadimageobject"); }