objective c - Downloading files in serial order using NSURLConnection in iOS -

i want download 3 files in serial order. 2 of them txt files , 1 .gz file. using nsurlconnection download above files.

i new ios programming. have seen in other question in , google can use serial dispatch queue operation serially.

but don't know how nsurlconnection. tried below did not work.

 dispatch_queue_t serialqueue = dispatch_queue_create("com.clc.propqueue", dispatch_queue_serial); dispatch_async(serialqueue, ^{     [self downloadprop]; }); dispatch_async(serialqueue, ^{     [self downloaddatabase]; }); dispatch_async(serialqueue, ^{     [self downloadtxt]; }); 

above code not executing connectiondidfinishloading of nsurlconnection. has idea how achieve this?

nsurlsession provides queue download each task in order in created.

nsurlsession *session = [nsurlsession sharedsession];  nsurlsessiontask *task1 = [session datataskwithurl:[nsurl urlwithstring:@"http://yahoo.com"] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {     nslog(@"complete 1"); }]; nsurlsessiontask *task2 = [session datataskwithurl:[nsurl urlwithstring:@"http://msn.com"] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {     nslog(@"complete 2"); }]; nsurlsessiontask *task3 = [session datataskwithurl:[nsurl urlwithstring:@"http://google.com"] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {     nslog(@"complete 3"); }];  // regardless of order tasks "resumed" (aka started) execute synchronously in order added, above. [task3 resume]; [task1 resume]; [task2 resume]; 

update based on comments & chat:

to more deterministic on ordering & execution of tasks...

nsurlsession *session = [nsurlsession sharedsession];  __block nsurlsessiontask *task1 = nil; __block nsurlsessiontask *task2 = nil; __block nsurlsessiontask *task3 = nil;  task1 = [session datataskwithurl:urltofirstfile completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {     // check error     nslog(@"first file completed downloading");     [task2 resume]; }]; task2 = [session datataskwithurl:urltosecondfile completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {     // check error     nslog(@"second file completed downloading");     [task3 resume]; }]; task3 = [session datataskwithurl:[nsurl urlwithstring:@"http://google.com"] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {     // check error     nslog(@"third file completed downloading"); }];  [task1 resume];