Mac 上 collectionview 单元格中的 UITextView 尖峰 cpu

Question

I have a simple UIKit application that has a UITextView in a UICollectionViewCell . The app is designed for iOS/iPadOS and works just fine on those platforms. However, when run on Mac (Designed for iPad) as soon as I start scrolling the collectionview, the cpu usage spikes to ~85% and stays there indefinitely. The only way to lower the cpu is to click outside of the application window, but once it comes to the foreground again, the cpu usage jumps right back up. I've tried running on Mac in Catalyst mode too, but the same problem occurs with slightly less cpu usage (~45%).

Additionally the debugger constantly spits out [API] cannot add handler to 3 from 3 - dropping while scrolling.

Does anyone have an explanation or solutions for this?

I'm using Xcode Version 14.1 (14B47b) on macOS Ventura 13.0 (22A380).

class ViewController: UIViewController {
    var dataSource: UICollectionViewDiffableDataSource<Section, String>! = nil
    var collectionView: UICollectionView! = nil
    var items = Array(0...100).map{"Item \($0)"}
    
    enum Section: String {
        case main
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        navigationItem.title = "List"
        configureCollectionView()
        configureDataSource()
        applyInitialSnapshot()
    }
    
    private func createLayout() -> UICollectionViewLayout {
        return UICollectionViewCompositionalLayout { sectionIndex, layoutEnvironment in
            let size = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .estimated(100))
            let item = NSCollectionLayoutItem(layoutSize: size)
            let group = NSCollectionLayoutGroup.horizontal(layoutSize: size, subitems: [item])
            
            return NSCollectionLayoutSection(group: group)
        }
    }
    
    private func configureCollectionView() {
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: createLayout())
        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        collectionView.backgroundColor = .systemBackground
        view.addSubview(collectionView)
    }
    
    private func configureDataSource() {
        let cellRegistration = UICollectionView.CellRegistration<TestCell, String> { (cell, indexPath, item) in
            cell.configure(title: item, row: indexPath.item)
        }
        
        dataSource = UICollectionViewDiffableDataSource<Section, String>(collectionView: collectionView) {
            (collectionView, indexPath, identifier) -> UICollectionViewCell? in
            
            return collectionView.dequeueConfiguredReusableCell(using: cellRegistration, for: indexPath, item: identifier)
        }
    }
    
    private func applyInitialSnapshot() {
        var snapshot = NSDiffableDataSourceSnapshot<Section, String>()
        snapshot.appendSections([.main])
        snapshot.appendItems(items)
        
        dataSource.apply(snapshot, animatingDifferences: false)
    }
}

class TestCell: UICollectionViewCell {
    private let annotationsTextView = UITextView()

    override init(frame: CGRect) {
        super.init(frame: frame)
        addViews()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func configure(title: String, row: Int) {
        annotationsTextView.attributedText = .init(string: "Row: \(row) Item: \(title)", attributes: [.font: UIFont.preferredFont(forTextStyle: .title1)])
    }
    
    private func addViews() {
        annotationsTextView.isScrollEnabled = false
        annotationsTextView.isEditable = false
        annotationsTextView.translatesAutoresizingMaskIntoConstraints = false
        
        contentView.addSubview(annotationsTextView)
        
        NSLayoutConstraint.activate([
            annotationsTextView.topAnchor.constraint(equalTo: contentView.topAnchor),
            annotationsTextView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
            annotationsTextView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
            annotationsTextView.trailingAnchor.constraint(equalTo:  contentView.trailingAnchor),
        ])
    }
}

Answer 1

I'm experiencing this exact behavior in Ventura whenever there is a UITextView anywhere in the view hierarchy with either isSelectable or isEditable set to true, but only while the UITextView is NOT first responder. This occurs whether the UITextView is visible or hidden.

The excess CPU usage can be prevented by any of the following:

• Remove the UITextView from the view hierarchy.
• Set isSelectable AND isEditable to false.
• Make the UITextView first responder.

I'm still investigating and will update here if I find more. We should all probably report the issue to Apple as I imagine they will need to fix this at the system level.

2022-12-01: Update

This issue appears to have been resolved as of macOS 13.1 beta 4 (22C5059b). Hallelujah!

Answer 2

I am still on 13.0.1 and had the same problem (tons of [API] cannot add handler to 3 from 3 - dropping). Was able to narrow it down to a call to UITableView.scrollToNearestSelectedRow with animated = true.

Setting animated to false stops the logging. I guess I'll have to check out 13.1