Change UICollectionViewCell size on different device orientations

1) You could maintain and swap out multiple layout objects, but there's a simpler way. Just add the following to your UICollectionViewController subclass and adjust the sizes as required:

- (CGSize)collectionView:(UICollectionView *)collectionView                  layout:(UICollectionViewLayout *)collectionViewLayout  sizeForItemAtIndexPath:(NSIndexPath *)indexPath{        // Adjust cell size for orientation    if (UIDeviceOrientationIsLandscape([[UIApplication sharedApplication] statusBarOrientation])) {        return CGSizeMake(170.f, 170.f);    }    return CGSizeMake(192.f, 192.f);}- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation{    [self.collectionView performBatchUpdates:nil completion:nil];}

Calling -performBatchUpdates:completion: will invalidate the layout and resize the cells with animation (you can just pass nil to both block params if you've no extra adjustments to perform).

2) Instead of hardcoding the item sizes in -collectionView:layout:sizeForItemAtIndexPath, just divide the height or width of the collectionView's bounds by the number of cells you want to fit on screen. Use the height if your collectionView scrolls horizontally or the width if it scrolls vertically.

If you don't want additional animations brought by performBatchUpdates:completion:, just use invalidateLayout to force the collectionViewLayout to reload.

- (void)viewWillLayoutSubviews{    [super viewWillLayoutSubviews];    [self.collectionView.collectionViewLayout invalidateLayout];}

I solved using two UICollectionViewFlowLayout. One for portrait and one for landscape. I assign them to my collectionView dinamically in -viewDidLoad

self.portraitLayout = [[UICollectionViewFlowLayout alloc] init];self.landscapeLayout = [[UICollectionViewFlowLayout alloc] init];UIInterfaceOrientation orientationOnLunch = [[UIApplication sharedApplication] statusBarOrientation];if (UIInterfaceOrientationIsPortrait(orientationOnLunch)) {    [self.menuCollectionView setCollectionViewLayout:self.portraitLayout];} else {    [self.menuCollectionView setCollectionViewLayout:self.landscapeLayout];}

Then I simply modified my collectionViewFlowLayoutDelgate Methods like this

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath{    CGSize returnSize = CGSizeZero;    if (collectionViewLayout == self.portraitLayout) {        returnSize = CGSizeMake(230.0, 120.0);    } else {        returnSize = CGSizeMake(315.0, 120.0);    }    return returnSize;}

Last I switch from a layout to one other on rotation

- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation{    if (UIInterfaceOrientationIsPortrait(fromInterfaceOrientation)) {        [self.menuCollectionView setCollectionViewLayout:self.landscapeLayout animated:YES];    } else {        [self.menuCollectionView setCollectionViewLayout:self.portraitLayout animated:YES];    }}