How to set UICollectionViewDelegateFlowLayout?

Question

A UIViewController maintains a reference to a UICollectionView. The controller should modify the built-in flow layout using the UICollectionViewDelegateFlowLayout.

I

Answer 1

My two cents for macOS Mojave - Swift

(I've fallen here searching for NSCollectionView... I do know question was about UICollectionView..)

All said above (specifying delegate implies cell size, too) is correct for macOS, too.

NOTE: If You write:

class MyViewController:
    NSCollectionViewDelegate,
    NSCollectionViewDataSource,
    **NSCollectionViewDelegateFlowLayout** 
{

the method:

func collectionView(_ collectionView: NSCollectionView, 
                      layout collectionViewLayout: NSCollectionViewLayout, 
               sizeForItemAt indexPath: IndexPath) -> NSSize

will be called.

If removed, no delegate method will be called. (as class does not obey to the protocol).