How do I define the size of a CollectionView on rotate

Question

I have a viewcontroller with 2 CollectionView Controllers.

I would like on rotation that only one of the collection views resize to a custom size while the other re

Answer 1

I've handled this by detecting the orientation change in the setBounds: method. We subclass the UICollectionView and override the setBounds: method (see below). In flowLayoutForGallerySize we create a new UICollectionViewFlowLayout with different spacing and itemSize depending on the size of the collection view.

- (void)setBounds:(CGRect)bounds
{
    // detect orientation changes and update itemSize in the flow layout
    CGSize oldSize = self.bounds.size;

    [super setBounds:bounds];

    BOOL wasLandscape = (oldSize.width > oldSize.height);
    BOOL nowLandscape = (bounds.size.width > bounds.size.height);

    if (wasLandscape != nowLandscape) {
        // create a new flow layout object for the new gallery size
        self.flowLayout = [self flowLayoutForGallerySize:bounds.size];

        // change to the new flow layout
        [self setCollectionViewLayout:self.flowLayout animated:NO];

        DLog(@"orientation change to %@", NSStringFromCGSize(bounds.size));
    }
}