Question

Not sure if this is the right title for this question or not..anyways,
I have an array of dictionaries and I am iterating through the dictionaries, passing in a block that gets executed sometimes in the future (asynchronous) and saving the result in a dictionary. Here’s my method:

- (void)elcImagePickerController:(ELCImagePickerController *)picker didFinishPickingMediaWithInfo:(NSArray *)info {

    NSLog(@"%@", info);
    NSMutableDictionary *images = [NSMutableDictionary dictionaryWithCapacity:[info count]];

    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    for (NSDictionary *dict in info) {
        NSURL *assetURL = [dict objectForKey:UIImagePickerControllerReferenceURL];

        [library assetForURL:assetURL
                 resultBlock:^(ALAsset *asset)  {
                     NSString *filename = asset.defaultRepresentation.filename;
                     UIImage *image = [dict objectForKey:UIImagePickerControllerOriginalImage];
                     [images setObject:filename forKey:image];
                 }
                failureBlock:^(NSError *error) {
                    [SVProgressHUD dismissWithError:@"Error occured."];
                }
         ];
    }

    NSLog(@"%@", images);

    [library autorelease];
    [self dismissImagePickerVC];
}

Ofcourse, at the end of this method, images is empty, but my question is, how can I get a call back when all the blocks for each iteration has been executed?
Thansk

Answer 1

From Apple’s documentation:

When the enumeration is done, enumerationBlock is invoked with group set to nil.

When enumeration is done, your first block will see asset == nil.