Ios – Resize UICollectionView cells after image inside has been downloaded

iosuicollectionviewuicollectionviewcell

I'm building a UICollectionView and my custom cells will contain two labels and one image.

Each image is downloaded asynchronously so I don't know it's size until the download it's complete.
Once is downloaded, I want to adapt each cell to re-layout it's content and frame to fit in height the image just downloaded.

As UICollectionViewLayout, I'm using CHTCollectionViewWaterfallLayout

To download the image asynchronously I'm using SDWebImage, like this:

    [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                   placeholderImage:[UIImage imageNamed:@"placeholder.png"]
                          completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType) 
                                {... some completion code here ...}];

QUESTION:

What is the right approach to resize each UICollectionViewCell right after the image is downloaded?

Best Answer

You should just be able to invalidate your collection view layout in an animation block when the image comes back. Things might get a little complicated if more than one image finishes completion at once, but this should work: 

[cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
               placeholderImage:[UIImage imageNamed:@"placeholder.png"]
                      completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType)^{
                          [UIView animateWithDuration:0.3f animations:^{
                              [self.collectionView.collectionViewLayout invalidateLayout];
                          }];
                      }];

Then just return a different size in the appropriate delegate method. 

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    return /* a different size if the image is done downloading yet */;
}
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