NSCollectionView crashes when creating items

Question

My NSCollectionView crashes when calling makeItem(withIdentifier identifier: String, for indexPath: IndexPath). numberOfItemsInSection returns the correct value. If I call makeItem... in viewDidLoad rather than in itemForRepresentedObject I see an error indicating that the indexPath is out of bounds. How can this be?

The collection view loads like this:

class TagCollectionViewController: NSViewController, NSCollectionViewDataSource {

  fileprivate static let itemIdentifier = "TagItem"

  @IBOutlet var collectionView: NSCollectionView!
  fileprivate var tags = List<Tag>.init()

  override func viewDidLoad() {
    super.viewDidLoad()

    let nib = NSNib(nibNamed: "TagCollectionViewItem", bundle: nil)
    collectionView.register(nib, forItemWithIdentifier: TagCollectionViewController.itemIdentifier)

    collectionView.dataSource = self
}

(The List collection is a Realm class)

During viewWillAppear() the tags collection is populated from a ReSwift state:

override func viewWillAppear() {
  for image in mainStore.state.selectedImages {
    for tag in image.tags {
      tags.append(tag)
    }
  }

  super.viewWillAppear()
}

Answer 1

Solved it.

When I created the .xib for the item I added an NSCollectionViewItem object but didn't wire up the view to my custom view.

To recap, for anyone who gets caught out by this, the steps to creating a NSCollectionViewItem are:

1. Create the nib and configure your views
2. Add an NSCollectionViewItem object to your nib
3. Wire up your view (and any other views) to the object
4. Register the nib with the collectionView in your view controller