Resize UICollectionView cells after image inside has been downloaded
Solution 1
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 */;
}
Solution 2
To resize collection view cells, you could reload the collection view and return the size of you collection view cells dynamically in the method:
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [collectionView cellForItemAtIndexPath:indexPath];
return [cell size];
}
In cases when the cell's size is dynamic, get the cell from the index path and return its size based on the size of the image. I usually create a method for the cell to return a dynamic size, like in the example above. You can use UIImage's size property to help return the size based on the image.
Fmessina
Updated on June 15, 2022Comments
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Fmessina about 2 years
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 CHTCollectionViewWaterfallLayoutTo 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? -
Fmessina about 10 yearsWhen should I reload the collection view, after all the images are downloaded? Or it's better to reload each cell with reloadItemsAtIndexPaths?
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Fmessina about 10 yearsThanks! I'm getting a perfect result the first time the UICollectionView is loaded, but when it's loaded for the second time (i.e. moving to another view and coming back) I get weird cell frame sizes (smaller than expected, with content overlapping). If I scroll a bit, everything is displayed properly again. Do I have to change the cell frame size (and where) after the image is downloaded?
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Fmessina about 10 yearsSolved. Actually there was nothing do nothing with the cell frame. I just had to set the cell.imageView frame just before the animateWithDuration block.
[cell.imageView setFrame:CGRectMake(2,2,image.size.width,image.size.height])]; [UIView animateWithDuration:0.3f animations:^{ [self.collectionView.collectionViewLayout invalidateLayout]; }];
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Chris about 10 yearsDoing it in this way you would have to reload the collection view after downloading all of the images.
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Fmessina about 10 years+1 because even if your answer didn't solve my issue, I used the idea of a [cell size] method. However @Ash solution was what I was looking for.
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Lion789 about 10 yearsShould I be calling it this way with a callback because if I do I have an issue since it expects a return expression, since I have it called on each cell? stackoverflow.com/questions/23316634/… That is how I wrote it, and was actually trying the resize but it does not keep the aspect ratio and instead cuts out a piece of the image?
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Matt over 9 yearsYou should not call dequeueReusableCellWithReuseIdentifier: multiple times without returning the cell to the collection, e.g. in cellForItemAtIndexPath:. The collection will have hundreds of dequeued cells sitting around that are never returned to be reused.
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Chris over 9 years@Matt, thanks for pointing that out! I updated the answer to use
cellForItemAtIndexPath:
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Waqar Khalid almost 6 yearsWhat did you return in size sizeForItemAtIndexPath method?