Correct way for to scroll after of reloadData completion

// correct way for to scroll, or execute a block of code, only after of reloadData completion
[self.collectionView reloadData];
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
    // scroll to item
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:3 inSection:0];
    [self.collectionView selectItemAtIndexPath:indexPath animated:YES scrollPosition:UICollectionViewScrollPositionLeft];
}];