I want to add some animation to the *imageView* with the `SDWebImage`.and my *collectionView* delegate function is here

```
- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath
{    
    Cell *cell = (Cell *)[cv dequeueReusableCellWithReuseIdentifier:@"identifier" forIndexPath:indexPath];

    [cell.imageView sd_setImageWithURL:[NSURL URLWithString:URL] completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {   
        cell.imageView.alpha = 0;
        [UIView animateWithDuration:0.5 animations:^{
            cell.imageView.alpha = 1;
        }];    
    }];
}

```

It's OK during the *SDWebImage* download the image and set the image of the *imageView*.
But when I call the `[collection reloadData]` method,these *imageViews* dissolve again.

I know the reason but I do not have a solution of it.