uicollectionview - indexPathForPreferredFocusedView is not being Called

Question

I need to specify which cell should receive focus.

According to Apple Documentation the indexPathForPreferredFocusedView delegate method should be called if the remembersLastFocusedIndexPath property is false, or if there is no saved index path because no cell was previously focused.

In my case I am using a collection view in a UIViewController and setting remembersLastFocusedIndexPath to false but indexPathForPreferredFocusedView is not being called.

How explain this behaviour?

Answer 1

The function indexPathForPreferredFocusedView is part of UICollectionViewDelegate, so it might be that the delegate was not assigned to your collectionView.

Or, the problem might also be on the focus environment, not taking into account your UICollectionView.

As a reference, here you have an example of a simple collectionView with 5 cells, having the one in the center initially selected by default

import UIKit

class ViewController: UIViewController {

    private var collectionView: UICollectionView!
    private var items = ["One", "Two", "Three", "Four", "Five"]

    override var preferredFocusEnvironments: [UIFocusEnvironment] {
        return [collectionView]
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: UICollectionViewFlowLayout())
        collectionView.remembersLastFocusedIndexPath = false
        MyCell.register(in: collectionView)
        view.addSubview(collectionView)

        collectionView.dataSource = self
        collectionView.delegate = self
    }
}

extension ViewController: UICollectionViewDataSource {

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return items.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MyCell.reuseIdentifier, for: indexPath) as! MyCell
        cell.titleLabel.text = items[indexPath.row]
        return cell
    }
}

extension ViewController: UICollectionViewDelegate {

    func indexPathForPreferredFocusedView(in collectionView: UICollectionView) -> IndexPath? {
            return IndexPath(row: 2, section: 0)
    }
}

class MyCell: UICollectionViewCell {

    static var reuseIdentifier: String { return String(describing: self) + "ReuseIdentifier" }

    var titleLabel: UILabel!

    public static func register(in collectionView: UICollectionView) {
        collectionView.register(MyCell.self, forCellWithReuseIdentifier: MyCell.reuseIdentifier)
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        titleLabel = UILabel(frame: bounds)
        backgroundColor = .blue
        contentView.addSubview(titleLabel)
    }

    override func didUpdateFocus(in context: UIFocusUpdateContext, with coordinator: UIFocusAnimationCoordinator) {
        backgroundColor = isFocused ? .red : .blue
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}