iOS UICollectionView prototype cell size property ignored

Question

I'm using a UICollectionView with two prototype cells. The prototype cells have different widths and contain different controls (image view and web view). I'm definitely returning the correct prototype cell for a given index (all the cells display the correct content), but the prototype cell size is ignored and the collection view's item size is used instead. It's not like I'm manually setting the size. What's the point of allowing the prototype cell to be sized in storyboard if the property is just ignored when it's actually displayed?

Answer 1

The size of the cell in the storyboard editor is just to help you design the cell. Since each prototype cell can be a different size, UICollectionView doesn't know which cell's size to pick for all the cells. That's why you set the actual size you want to use for your cells separately. You can do it in the designer by selecting the collection view and setting its Cell Size Width and Height in the Size inspector, under the "Collection View Size" heading.

Or, you can override the following method and return a CGSize object that specifies the size you want to use for each cell. Using this method, you can actually have each cell be a different size:

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath

Example:

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    return CGSizeMake(100, 100);
}

Your view controller needs to be a delegate of UICollectionViewDelegateFlowLayout in order for this method to be called. So don't forget to add that delegate declaration to your view controller's .h file, such as:

@interface MyViewController () <UICollectionViewDelegateFlowLayout>

Swift

extension MyViewController : UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: 100, height: 100)
    }
}

Answer 2

If all the cells are the same size and you can set the itemSize on the UICollectionViewFlowLayout

Example:

((UICollectionViewFlowLayout *) self.collectionViewLayout).itemSize = CGSizeMake(100, 100);

Answer 3

Swift, working for latest iOS.

(collectionView.collectionViewLayout as! UICollectionViewFlowLayout).itemSize = cellSize

I don't have enough points to reply to Sam, but the key is that it's not UICollectionViewLayout but UICollectionViewFlowLayout.

Answer 4

I had a Similar Issue, I set a breakpoint on the sizeForItemAt and it was being called for every cell I had on my collection, however, the size set in code was never being reflected on the device.

While looking at other collections in my project I noticed the Collection View Flow Layout was slightly different in the collection with the issue.

By Selecting the Flow Layout in the Storyboard

And then Setting the Cell Size & Estimate Size in the Size Inspector

This helped me solve my issue.

However the size of the cell will not be dynamic with what is in your sizeForItemAt