ios - Return value in NSURLSession Error -

i below error while trying return responsestring

incompatible block pointer types sending 'nsstring *(^)(nsdata *__strong, nsurlresponse *__strong, nserror *__strong)' parameter of type 'void (^)(nsdata *__strong, nsurlresponse *__strong, nserror *__strong)'

where call suppose aviewcontroller class

nsstring *responsestring=[self callapi]; 

and below code in bviewmodel class:

-(nsstring* )callapi {     nsurlsessionconfiguration *configuration = [nsurlsessionconfiguration defaultsessionconfiguration];     nsurlsession *session = [nsurlsession sessionwithconfiguration:configuration delegate:self delegatequeue:nil];     nsurl *url = [nsurl urlwithstring:@"http://appersgroup.com/talkawalk/login.php?email=twalknet@gmail.com&password=123456&latitude=52.486245&longitude=13.327496&device_token=show"];     nsmutableurlrequest *request = [nsmutableurlrequest requestwithurl:url                                                            cachepolicy:nsurlrequestuseprotocolcachepolicy                                                        timeoutinterval:60.0];      [request addvalue:@"application/json" forhttpheaderfield:@"content-type"];     [request addvalue:@"application/json" forhttpheaderfield:@"accept"];      [request sethttpmethod:@"post"];     /* nsdictionary *mapdata = [[nsdictionary alloc] initwithobjectsandkeys: @"test ios", @"name",      @"ios type", @"typemap",      nil];      nsdata *postdata = [nsjsonserialization datawithjsonobject:mapdata options:0 error:&error];      [request sethttpbody:postdata];      */      nsurlsessiondatatask *postdatatask = [session datataskwithrequest:request completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {          nsstring* responsestring = [[nsstring alloc] initwithdata:data encoding:nsutf8stringencoding];          if([responsestring rangeofstring:@"nil"].location != nsnotfound)         {             nsstring * newresponse =  [[nsstring alloc] initwithdata:data encoding:nsasciistringencoding];              responsestring = newresponse;         }          nslog(@"%@",responsestring);         nslog(@"response %@",response);         nslog(@"error %@",error);          return responsestring;//adding line give me error ? how return value        }];      [postdatatask resume]; } 

you can use method block :

-(void)callapiwithcompletionhandler : (void (^) (nsstring * strresponse)) completionhandler {     nsurlsessionconfiguration *configuration = [nsurlsessionconfiguration defaultsessionconfiguration];     nsurlsession *session = [nsurlsession sessionwithconfiguration:configuration delegate:self delegatequeue:nil];     nsurl *url = [nsurl urlwithstring:@"http://appersgroup.com/talkawalk/login.php?email=twalknet@gmail.com&password=123456&latitude=52.486245&longitude=13.327496&device_token=show"];     nsmutableurlrequest *request = [nsmutableurlrequest requestwithurl:url                                                            cachepolicy:nsurlrequestuseprotocolcachepolicy                                                        timeoutinterval:60.0];      [request addvalue:@"application/json" forhttpheaderfield:@"content-type"];     [request addvalue:@"application/json" forhttpheaderfield:@"accept"];      [request sethttpmethod:@"post"];     /* nsdictionary *mapdata = [[nsdictionary alloc] initwithobjectsandkeys: @"test ios", @"name",      @"ios type", @"typemap",      nil];      nsdata *postdata = [nsjsonserialization datawithjsonobject:mapdata options:0 error:&error];      [request sethttpbody:postdata];      */      nsurlsessiondatatask *postdatatask = [session datataskwithrequest:request completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {          nsstring* responsestring = [[nsstring alloc] initwithdata:data encoding:nsutf8stringencoding];          if([responsestring rangeofstring:@"nil"].location != nsnotfound)         {             nsstring * newresponse =  [[nsstring alloc] initwithdata:data encoding:nsasciistringencoding];              responsestring = newresponse;         }          nslog(@"%@",responsestring);         nslog(@"response %@",response);         nslog(@"error %@",error);          completionhandler(responsestring);      }];      [postdatatask resume]; } 

call method , return response below :

[self callapiwithcompletionhandler:^(nsstring *strresponse) {          nsstring *responsestring = strresponse; }]; 

suppose method implemented in viewcontrollera, , want call viewcontrollerb.

then import viewcontrollera in viewcontrollerb , make instance of viewcontrollera in viewcontrollerb.

viewcontrollera *vca = [[viewcontrollera alloc] init]; [vca callapiwithcompletionhandler:^(nsstring *strresponse) {          nsstring *responsestring = strresponse; }];