Updating images in application coming from photo gallery using ALAssetsLibrary
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    if (!assetsLibrary) {
        assetsLibrary = [[ALAssetsLibrary alloc] init];
    }
    if (!groups) {
        groups = [[NSMutableArray alloc] init];
    }
        else {
            [groups removeAllObjects];
        }

    ALAssetsLibraryGroupsEnumerationResultsBlock listGroupBlock = ^(ALAssetsGroup *group, BOOL *stop) {

        if (group) {
            [groups addObject:group];
        } else {
            [self displayImages];
        }
    };

    ALAssetsLibraryAccessFailureBlock failureBlock = ^(NSError *error) {
        NSString *errorMessage = nil;
        switch ([error code]) {
            case ALAssetsLibraryAccessUserDeniedError:
            case ALAssetsLibraryAccessGloballyDeniedError:
                errorMessage = @"The user has declined access to it.";
                break;
            default:
                errorMessage = @"Reason unknown.";
                break;
        }
    };
    [assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:listGroupBlock failureBlock:failureBlock];
}
- (void)displayImages{
    for (int i = 0 ; i< [groups count]; i++) {
        assetsGroup = [groups objectAtIndex:i];
        if (!assets) {
            assets = [[NSMutableArray alloc] init];
        }
            else {
                [assets removeAllObjects];
            }

        ALAssetsGroupEnumerationResultsBlock assetsEnumerationBlock = ^(ALAsset *result, NSUInteger index, BOOL *stop) {

            if (result) {
                [assets addObject:result];
            }
        };
        ALAssetsFilter *onlyPhotosFilter = [ALAssetsFilter allPhotos];
        [assetsGroup setAssetsFilter:onlyPhotosFilter];
        [assetsGroup enumerateAssetsUsingBlock:assetsEnumerationBlock];

           }
    [gridView reloadData];

}