ios - method returns before completionhandler -

i developing networkutil project, need method gets url , returns json received url using nsurlsessiondatatask json server. method following:

+ (nsdictionary*) getjsondatafromurl:(nsstring *)urlstring{     __block nsdictionary* jsonresponse;     nsurlsession *session = [nsurlsession sharedsession];     nsurlsessiondatatask *datatask = [session datataskwithurl:[nsurl urlwithstring:urlstring] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {         jsonresponse = [nsjsonserialization jsonobjectwithdata:data options:0 error:nil];         nslog(@"%@", jsonresponse);     }];      [datatask resume];      return jsonresponse; } 

the problem completionhandler inside method , method itself run on different threads , in last line jsonresponse nil

how should set jsonresponse returned json urlstring?
best practice issue?

block running in nsurlsession running on different thread - method doesn't wait block finish.

you have 2 options here

first one. send nsnotification

+ (void) getjsondatafromurl:(nsstring *)urlstring{        nsurlsession *session = [nsurlsession sharedsession];        nsurlsessiondatatask *datatask = [session datataskwithurl:[nsurl urlwithstring:urlstring] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {            nsdictionary* jsonresponse = [nsjsonserialization jsonobjectwithdata:data options:0 error:nil];            nslog(@"%@", jsonresponse);             [[nsnotificationcenter defaultcenter] postnotificationname:@"jsonresponse" object:nil userinfo:@{@"response" : jsonresponse}];        }];         [datatask resume]; } 

second one. past completion block utility method

+ (void) getjsondatafromurl:(nsstring *)urlstring             completionblock:(void(^)(nsdictionary* response))completion {        nsurlsession *session = [nsurlsession sharedsession];        nsurlsessiondatatask *datatask = [session datataskwithurl:[nsurl urlwithstring:urlstring] completionhandler:^(nsdata *data, nsurlresponse *response, nserror *error) {            nsdictionary* jsonresponse = [nsjsonserialization jsonobjectwithdata:data options:0 error:nil];            nslog(@"%@", jsonresponse);             completion(jsonresponse);        }];         [datatask resume]; }