Getting error while fetching picture of facebook friends with Graph API in iOS Social Framework

Question

I'm using below code to get facebook friends list, and its working fine. But there is a need of friends profile picture too.

NSString  *fbPermissions =  @[ @"user_about_me",@"email",@"user_friends"];
NSString  *apiIdKey = @"App_Key";

ACAccountStore *accountStore = [[ACAccountStore alloc] init];
id options = @{
                   ACFacebookAppIdKey: apiIdKey,
                   ACFacebookPermissionsKey: fbPermissions,
                   ACFacebookAudienceKey: ACFacebookAudienceFriends,
              };

ACAccountType *accountType = [accountStore accountTypeWithAccountTypeIdentifier:    ACAccountTypeIdentifierFacebook];
[accountStore requestAccessToAccountsWithType:accountType options:options completion:^(BOOL granted, NSError *error)
{
     if (granted == YES)
     {
         NSArray *arrayOfAccounts = [accountStore accountsWithAccountType:accountType];

         ACAccount *tempAccount = [arrayOfAccounts lastObject];
         NSString *string =  [NSString stringWithFormat:@"https://graph.facebook.com/me/friends"];

         NSURL *fbURL = [NSURL URLWithString:string];

         SLRequest *fbRequest = [SLRequest requestForServiceType:SLServiceTypeFacebook
                                                          requestMethod:SLRequestMethodGET
                                                                    URL:fbURL
                                                             parameters:nil];

             [fbRequest setAccount:tempAccount];

             [fbRequest performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error) {

                 if (!error)
                 {

                     NSError *jsonError = nil;
                     NSDictionary *data = [NSJSONSerialization JSONObjectWithData:responseData
                                                                          options:NSJSONReadingAllowFragments
                                                                            error:&jsonError];

                     NSMutableArray *array = [data valueForKey:@"data"];
                     NSLog(@"Friends array:- %@",array);



                 }
                 else
                 {
                     [[[UIAlertView alloc]initWithTitle:@"Error"
                                                message:[error description]
                                               delegate:nil
                                      cancelButtonTitle:@"OK"
                                      otherButtonTitles:nil, nil] show];
                 }
             }];
         }
     }];

To get profile picture I have changed request url with:-

NSString *string =  [NSString stringWithFormat:@"https://graph.facebook.com/me/friends?fields=picture,name"];

I got following response :-

{
error =     {
    code = 2500;
    message = "An active access token must be used to query information about the current user.";
    type = OAuthException;
};
}

I'm not sure its access token expiration error because to revert back request Url to previous one, code works fine.

Answer 1

Finally it worked with:-

NSString *string =  [NSString stringWithFormat:@"https://graph.facebook.com/me/friends"];

NSURL *requestURL = [NSURL URLWithString:@"https://graph.facebook.com/me/friends"];

SLRequest *fbRequest = [SLRequest requestForServiceType:SLServiceTypeFacebook
                                                   requestMethod:SLRequestMethodGET URL:requestURL parameters:@{@"fields":@"id,name,picture,first_name,last_name,gender"}];