Error: UICollectionView must be initialized with a non-nil layout parameter

Question

I am trying to create a Facebook messenger like application from a youtube tutorial. I have a home page where the user click BarButton to open the chats. The Home page works

Answer 1

Probably when you present your ChatViewController you have something like:

let chatVC = ChatViewController()

But according to Apple doc:

class UICollectionViewController

When you initialize the controller, using the init(collectionViewLayout:) method, you specify the layout the collection view should have.

So you need:

 let chatVC = ChatViewController(collectionViewLayout: UICollectionViewFlowLayout())

Answer 2

Seems like you skipped steps in a tutorial which is using Interface Builder.

The problem is, that in your ChatViewController there is a missing connection between your "collectionView?" and the corresponding UICollectionView (so called referencing outlet) in the Interface Builder.

This is a very basic task in iOS development. Please have a look at the official Apple documentation under the topic "Create Outlets for UI Elements": Connect UI to Code