the behavior of the UICollectionViewFlowLayout is not defined, because the cell width is greater than collectionView width

Question

2015-08-18 16:07:51.523 Example[16070:269647] the behavior of the UICollectionViewFlowLayout is not defined because: 2015-08-18 16:07:51.523
Example

Answer 1

I've been struggling with this problem for some hours, too.

My UICollectionViewController is embedded in a container view, when rotating the iPad from landscape to portrait it showed the error. The cells did resize though.

I solved the error by calling the following in the UICollectionViewController:

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
    self.collectionView.collectionViewLayout.invalidateLayout()

    super.viewWillTransition(to: size, with: coordinator)
}

The "super" has to be called after invalidating the layout.

Additionally I needed to call the following in the view where the container view is embedded in:

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
    super.viewWillTransition(to: size, with: coordinator)

    DispatchQueue.main.async {
        self.collectionViewController.collectionView.reloadData()
    }
}

This way, the cells are updated after the screen rotation is done.