Focus on iPad keyboard navigation

override var canBecomeFocused: Bool { true }

class MyViewController: UICollectionViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        self.collectionView.allowsFocus = true
    }
}

class MyCollectionViewDelegate: NSObject, UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView,
                canFocusItemAt indexPath: IndexPath) -> Bool {
        return true
    }
}

po UIFocusDebugger.checkFocusability(for:)

let focusEffect = UIFocusHaloEffect(roundedRect: self.bounds, cornerRadius: self.layer.cornerRadius, curve: .continuous)
self.focusEffect = focusEffect

let focusEffect = UIFocusHaloEffect(roundedRect: self.bounds, cornerRadius: self.layer.cornerRadius, curve: .continuous)

// make sure the effect is added right above the image view
focusEffect.referenceView = self.imageView

// make sure the effect is added to our scroll view
focusEffect.containerView = self.scrollView

self.focusEffect = focusEffect

init(frame: CGRect) {
   super.init(frame: frame)
   self.focusEffect = nil
}

func didUpdateFocus(in context: UIFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
    if context.nextFocusedItem == self {
        // This view is focused. Customize its appearance.
    }
    else if context.previouslyFocusedItem == self {
        // This view was focused.
    }
}

var selectionFollowsFocus: Bool

func collectionView(_ collectionView: UICollectionView, selectionFollowsFocusForItemAt indexPath: IndexPath) -> Bool {
    return self.action(for: indexPath).type != .showAlert
}

self.focusGroupIdentifier = "com.myapp.groups.sidebar"

extension UIFocusGroupPriority {
    public static let ignored: UIFocusGroupPriority // 0
    public static let previouslyFocused: UIFocusGroupPriority // 1000
    public static let prioritized: UIFocusGroupPriority // 2000
    public static let currentlyFocused: UIFocusGroupPriority // NSIntegerMax
}

// Customizing an item’s focus group priority

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = ...
    if self.isCallToActionCell(at: indexPath) {
        // This cell is not as important as a selected cell but should
        // be chosen over the last focused cell in this group.
        cell.focusGroupPriority = .previouslyFocused + 10
    }
    return cell
}

po UIFocusDebugger.checkFocusGroupTree(for:)

keyCommand.wantsPriorityOverSystemBehavior = true

override func pressesBegan(_ presses: Set<UIPress>, with event: UIPressesEvent?) {
    if (/* check presses of interest */) {
        // handle the press
    }
    else {
        super.pressesBegan(presses, with: event)
    }
}