Using a while loop to stall until I get some data back

I have a class which I am using to interact with Facebook in Objective C for my iPhone application.


@interface GWFacebook : Facebook <FBRequestDelegate>
   bool query_running;
   NSArray* query_result;
- (void)request:(FBRequest *)request didFailWithError:(NSError *)error;
- (void)request:(FBRequest *)request didLoad:(id)result;
- (void)LogIn;
- (NSArray*)getAllFriends;



#import "GWFacebook.h"

@implementation GWFacebook
- (void)request:(FBRequest *)request didLoad:(id)result
 query_result = result;
 query_running = false;

- (NSArray*)getAllFriends
    NSMutableDictionary * params = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                @"SELECT first_name, last_name, uid, pic_big FROM user WHERE uid IN (SELECT uid2 FROM friend WHERE uid1 = me()) ORDER BY mutual_friend_count desc",@"query",nil];   
    query_running = true;
    bool localbool = true;
    [self requestWithMethodName: @"fql.query" andParams: params andHttpMethod: @"POST" andDelegate: self];
      localbool = query_running;

    return query_result;

Basically the function getAllFriends makes a fb request and sets this object as the facebook request delegate. The function request didLoad of the delegate (self) is then called and uses a variable to pass the data back to the getAllFriends function, which then returns it to whatever called it.

The long and short of it is that im trying to use a while loop to stall the function until it receives a response. In debugging, its clear that the request didload function is never called by the facebook object. It is called when I remove the while loop ... thus the data request is successful and the while loop is the problem.

Im wondering if there is a way to stall a function until the data is received...Im probably doing something very silly so I need some help!



The Facebook request will perform the delegate callback on your thread, which you block in the while loop. That is what is causing your problem.

As a matter of design, you have an API which works rather asyncronously, but you created a syncronous wrapper over it. Do you need to do it that way? I would recommend that you change your GWFacebook class to use a delegate or a block for returning the NSArray of friends.

- (void)getAllFriends:(void (^)(NSArray *))callbackBlock

This way you do not block your UI and you may find it easier to provide any kind of waiting indicators in your UI.

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