Change UICollectionViewCell size on different device orientations

Question

I am using an UICollectionView with UICollectionViewFlowLayout.

I set the size of each cell through the

collectionView:layout:sizeForItemAtIndexPath:

When switching from portrait to landscape, I would like to adjust the size of each cell to completely fit the size of the CollectionView, without leaving padding space between cells.

Questions:

1) How to change the size of a cell after a rotation event?

2) And, even better, how to make the layout where the cells always fit the entire size of the screen?

Answer 1

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.