ios - Is this the right way of using NSOperation (AFXMLRequestOperation)? -

in app have series of background tasks performed 1 after other (say tasks : a, b , c). each of these tasks talk different web services (xml). using afxmlrequestoperation of afnetworking library initiate request web service , handling parsing logic @ success block.

each following task dependent on successful completion of previous task. also, want following task called after delay of few seconds after successful completion of previous. once task c completes successfully, i'm done.

all of happening in background thread, , hence ui thread responsive throughout (my uiactivityindicator keeps moving throughout each tasks separately).

here's pseudo code snippet:

-(void)viewdidload {     _operationqueue = [[nsoperationqueue alloc]init];      [_operationqueue setmaxconcurrentoperationcount:1];           [self taska]; }  - taska {      nsmutableurlrequest *request = urla;      afxmlrequestoperation *operationa = [afxmlrequestoperation xmlparserrequestoperationwithrequest:request success:^(nsurlrequest *request, nshttpurlresponse *response, nsxmlparser *xmlparser) {         xmlparser.delegate = someclass;         [xmlparser parse];          // since operation successful, start task b after delay of 5 seconds         [self performselector:@selector(taskb) withobject:nil afterdelay:5];        failure:^(nsurlrequest *request, nshttpurlresponse *response, nserror *error, nsxmlparser *xmlparser) {         nslog(@"nserror: %@",error);      }];      [_operationqueue addoperation: operationa]; }  - taskb {      nsmutableurlrequest *request = urlb;      afxmlrequestoperation *operationb = [afxmlrequestoperation xmlparserrequestoperationwithrequest:request success:^(nsurlrequest *request, nshttpurlresponse *response, nsxmlparser *xmlparser) {         xmlparser.delegate = someotherclass;         [xmlparser parse];          // since operation successful, start task c after 10 seconds         [self performselector:@selector(taskc) withobject:nil afterdelay:10];        failure:^(nsurlrequest *request, nshttpurlresponse *response, nserror *error, nsxmlparser *xmlparser) {     }];       [_operationqueue addoperation: operationb];     [operationb adddependency:operationa]; // code seems produce no result , hence seems redundant }  - taskc {     nsmutableurlrequest *request = urlb;     afxmlrequestoperation *operationc = [afxmlrequestoperation xmlparserrequestoperationwithrequest:request success:^(nsurlrequest *request, nshttpurlresponse *response, nsxmlparser *xmlparser) {        xmlparser.delegate = yetanotherclass;        [xmlparser parse];      // since operation successful, mission accomplished!     nslog(@"mission accomplished!");         failure:^(nsurlrequest *request, nshttpurlresponse *response, nserror *error, nsxmlparser *xmlparser) {     }];      [_operationqueue addoperation: operationb];     [operationc adddependency:operationb]; // code seems produce no result , hence seems redundant } 

questions:

1. i'm able achieve wanted app implementation, i'm not sure if i'm making right use of nsoperation , nsoperationqueue. of read apple docs , tutorials, 1 of strengths of nsoperation using dependency establishment between different operations. however, in example how can ensure operationb gets executed after 'successful' completion of task , leverage "adddependency" feature of nsoperation?

2. i want ensure 'taskb' gets called after delay after successful completion of 'taska' , on. [self performselector:@selector(taskb) withobject:nil afterdelay:5];

   the way it? or there alternative ways, use elements of nsoperation/nsoperationqueues? or maybe use "dispatch_after"??

overall, how can redesign code better same tasks accomplished using nsoperation?