Call Completion Handler Method In for Loop

Question

I Have albumIds of FB users in one array, I want to get images for each Album for that I have to call following method with albumId, But I cant call this method in For Loop, I want all albums Images, Problem is that For loop executes without calling "FBRequestConnection startWithGraphPath:graphPath" Function so I am not getting Response The Problem Is Completion Handler Please tell me how to call method with completion Handler in For Loop

 arrAlbumIds=(11523252,11523245,11523278)

 for (int i=0; i<arrAlbumIds.count; i++) {



        NSString * graphPath=[NSString stringWithFormat:@"/%@/photos",[arrAlbumIds objectAtIndex:i]];

        [FBRequestConnection startWithGraphPath:graphPath
                                     parameters:nil
                                     HTTPMethod:@"GET"
                              completionHandler:^(
                                                  FBRequestConnection *connection,
                                                  id result,
                                                  NSError *error
                                                  ) {
                                  /* handle the result */

                                  NSLog(@"album images:%@",result);

                                  FBGraphObject * response=[[FBGraphObject alloc]init];
                                  response=result;

                                  NSMutableDictionary * dictImagesData=[[NSMutableDictionary alloc]init];
                                  dictImagesData=response;


                                  NSMutableArray * arrImagesData=[[NSMutableArray alloc]init];
                                  arrImagesData=[dictImagesData valueForKey:@"data"];


                                  FBGraphObject * fbGraphImages=[[FBGraphObject alloc]init];
                                  fbGraphImages=[arrImagesData valueForKey:@"images"];

                                  NSDictionary * dictImages=[[NSDictionary alloc]init];
                                  dictImages=fbGraphImages;

                                  NSMutableArray * arrImages=[[NSMutableArray alloc]init];
                                  arrImages=[arrImagesData valueForKey:@"images"];



                                  //Get Url of Each Image
                                  //self.arrFbAlbumImages=[[NSMutableArray alloc]init];

                                  [arrFacebookAlbumThumbnail addObject:[arrImages valueForKey:@"source"]];

                                  NSLog(@"arrFacebookAlbumThumbnail=%@",arrFacebookAlbumThumbnail);
                              }];
}

It is unclear exactly what you are asking. There is no recursion in this code — Paulw11, May 25 '14 at 09:04
FBRequestConnetion startWithGrapPath: This Method is being called in for loop but for loop execution is not waiting for completion handler thats why completion handler method is not called — user3673300, May 25 '14 at 09:07
This is just iteration. It is not recursion http://en.wikipedia.org/wiki/Recursion_(computer_science) The method is asynchronous as network operations take time. Your completion handler will be called when the task completes but you can expect `startWithGraphPath` to return immediately — Paulw11, May 25 '14 at 09:09
yes but how to call this method in for loop ? can you help me? — user3673300, May 25 '14 at 09:10
What isn't working with what you have now? It looks like you could have some issues with multi-threaded access to `arrFacebookAlbumThumbnail` — Paulw11, May 25 '14 at 09:23
For loop is executing but completion Handler block is not executed — user3673300, May 25 '14 at 09:27
I suggest you simplify - Try with just one element in the array, or remove the loop and just call for the first element of the array - does your completion handler get called then? — Paulw11, May 25 '14 at 09:29
Also - see this - http://stackoverflow.com/questions/18137976/facebook-ios-sdk-3-6-startwithgraphpath-completion-block-not-executed you may have a threading issue inside the FB API — Paulw11, May 25 '14 at 09:30
It works fine with one object without loop, But want to get data for all albums so I have to call this method for every albumId exist in array So I have only one way to do that is for loop — user3673300, May 25 '14 at 09:35

Paulw11 · Answer 1 · 2014-05-25T11:05:50.163

From your comments, it looks like the Facebook API doesn't like concurrent operations.

This code eliminates the for loop and invokes the next Facebook call in the completion handler

int i=0;

if (arrAlbumIds.count > 1)
{


  NSString * graphPath=[NSString stringWithFormat:@"/%@/photos",[arrAlbumIds objectAtIndex:i]];

  void (^completionBlock)(FBRequestConnection *connection,id result,NSError *error)= ^( FBRequestConnection *connection,
                         id result,
                         NSError *error) {
    NSLog(@"album images:%@",result);

    FBGraphObject * response=[[FBGraphObject alloc]init];
    response=result;

    NSMutableDictionary * dictImagesData=[[NSMutableDictionary alloc]init];
    dictImagesData=response;


    NSMutableArray * arrImagesData=[[NSMutableArray alloc]init];
    arrImagesData=[dictImagesData valueForKey:@"data"];


    FBGraphObject * fbGraphImages=[[FBGraphObject alloc]init];
    fbGraphImages=[arrImagesData valueForKey:@"images"];

     NSDictionary * dictImages=[[NSDictionary alloc]init];
     dictImages=fbGraphImages;

     NSMutableArray * arrImages=[[NSMutableArray alloc]init];
     arrImages=[arrImagesData valueForKey:@"images"];


     //Get Url of Each Image
     //self.arrFbAlbumImages=[[NSMutableArray alloc]init];

    [arrFacebookAlbumThumbnail addObject:[arrImages valueForKey:@"source"]];

    NSLog(@"arrFacebookAlbumThumbnail=%@",arrFacebookAlbumThumbnail);

    if (++i<arrAlbumIds.count) {
       NSString * graphPath=[NSString stringWithFormat:@"/%@/photos",[arrAlbumIds objectAtIndex:i]];
    [FBRequestConnection startWithGraphPath:graphPath
                                     parameters:nil
                                     HTTPMethod:@"GET"
                              completionHandler:completionBlock];
    }
  };

    [FBRequestConnection startWithGraphPath:graphPath
                                     parameters:nil
                                     HTTPMethod:@"GET"
                              completionHandler:completionBlock];

}

Does Not work for me, still [FBRequestConnection startWithGraphPath:graphPath parameters:nil HTTPMethod:@"GET" is never executed — user3673300, May 25 '14 at 10:33
If you put an NSLog in the dispatch block before the call to startWithGraphPath do you get that printed to the log? — Paulw11, May 25 '14 at 10:40
NSlog out side the fb completion handler is printed but FB compeletion handler log is not getting printed — user3673300, May 25 '14 at 10:46
I realise now that the because `startWithGraphPath` is asynchronous you will still have the same problem. I will revise my answer. — Paulw11, May 25 '14 at 10:51

Call Completion Handler Method In for Loop

1 Answers1