In my app , we have to make 3 server calls when we click on the login button.
1) will make a server call to get an OAuth token for user credentials
2) with the token from (1) we will get user privileges
3) with the token from (1) and with the valid privilege from (2) we will get the data to be displayed on the page after login in a tableview.
you can use
NSURLSession tasks. first call first api method and you will get response in completion handler(block). now store it in any public property (as you want to use it again) within completion handler. From that completion handler call second api method and from the completion handler of that second method, call third api method by passing response and using public property which have first api method's object stored.
Completion handler or blocks getting called only when response is arrived so by this way you can manage your api calls.
Hope this will help :)