I've been trying to replicate a specific type collection view using compositional layouts, and am not fully understanding how to use background items correctly.
The effect I am trying to recreate is the 'favorites' section of the initial Maps sheet:
As the user pans the orthogonal section, the background moves along with the items, even if the number of items grows past the width of the view.
However in my code, although I attach a NSCollectionLayoutDecorationItem.background to the decorationItems of the enclosing section, the background doesn't scroll with the items.
Do I need to instead create NSCollectionLayoutSupplementaryItems and attach them to the group for this effect? If so I am not understanding the correct process - if I create the layout group with NSCollectionLayoutGroup(layoutSize: layoutGroupSize, supplementaryItems: [item]) I can't add subitems later and if I use NSCollectionLayoutGroup.horizontal(layoutSize: layoutGroupSize, subitems: [items]) then I can't add supplementary items?