Animating UICollectionView on orientation changes

Question

Consider a UICollectionView that has a different number of items and a different layout (ie: spacing) on landscape and portrait orientation.

What needs to be done for these changes to be animated when the device is rotated? I couldn't find any mention of how to handle rotations on the Collection View Programming Guide.

Answer 1

It's not necessary to reload the collection view's data — invoking [collectionView.collectionViewLayout invalidateLayout] will cause the collection view to update its layout.

Overriding shouldInvalidateLayoutForBoundsChange: to return YES in a UICollectionViewLayout subclass will result in invalidateLayout being called automatically whenever the collection view's bounds change (including when its size changes and when the user scrolls its contents).

Answer 2

I had different number of sections based on the orientation, and the auto rotation didn't change it. I had to add a call to the collectionView to reload the data. I'm using a UICollectionViewController, adjust to your own collection view property if you have something else:

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(    NSTimeInterval)duration {
    [super willRotateToInterfaceOrientation:toInterfaceOrientation duration:duration];
    [self.collectionView reloadData];
}

Answer 3

The quickest way is a mix of all other answers.

just add the following lines in your ViewController :

override func willRotateToInterfaceOrientation(toInterfaceOrientation: UIInterfaceOrientation, duration: NSTimeInterval) {
    self.mCollectionView.collectionViewLayout.invalidateLayout()
}

You do not need to reloadData.