Mac端iPad适配App中UICollectionViewCell内嵌UITextView致CPU飙升

问题描述 #

我开发了一个简单的UIKit应用，在UICollectionViewCell中内嵌了UITextView，该应用在iOS/iPadOS平台运行正常，但在Mac（iPad适配模式）下，滚动UICollectionView时CPU占用率会飙升至约85%并持续居高不下，仅当点击应用窗口外部切换到后台时CPU占用才会下降，切回前台后又立刻回升。我也尝试了Catalyst模式，同样存在该问题，只是CPU占用率略低（约45%）。

此外，滚动时调试器持续输出日志：[API] cannot add handler to 3 from 3 - dropping

请问有人能解释该问题或提供解决方案吗？

环境信息 #

• Xcode Version 14.1 (14B47b)
• macOS Ventura 13.0 (22A380)

代码示例 #

ViewController代码 #

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)
    }
}

TestCell代码 #

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),
        ])
    }
}

问题原因与解决方案 #

问题原因 #

这个问题源于UITextView在Mac的iPad适配/Catalyst模式下的底层交互逻辑冗余：即使禁用了滚动和编辑功能，UITextView仍会保留文本选择、富文本编辑等相关的后台处理逻辑，当CollectionView滚动复用单元格时，这些逻辑会被频繁触发，导致大量不必要的计算，进而引发CPU占用飙升。调试日志[API] cannot add handler to 3 from 3 - dropping也反映了UITextView在Mac平台上的交互处理存在内部冲突。

解决方案 #

方案1：替换UITextView为UILabel（推荐）

由于你的场景仅需展示文本，无需编辑或滚动功能，UILabel是更轻量、性能更稳定的替代方案，完全支持富文本展示。修改后的TestCell代码如下：

class TestCell: UICollectionViewCell {
    private let annotationsLabel = UILabel()

    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) {
        annotationsLabel.attributedText = .init(string: "Row: \(row) Item: \(title)", attributes: [.font: UIFont.preferredFont(forTextStyle: .title1)])
    }
    
    private func addViews() {
        annotationsLabel.numberOfLines = 0 // 支持多行文本换行
        annotationsLabel.translatesAutoresizingMaskIntoConstraints = false
        
        contentView.addSubview(annotationsLabel)
        
        NSLayoutConstraint.activate([
            annotationsLabel.topAnchor.constraint(equalTo: contentView.topAnchor),
            annotationsLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
            annotationsLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
            annotationsLabel.trailingAnchor.constraint(equalTo:  contentView.trailingAnchor),
        ])
    }
}

方案2：优化UITextView配置（需保留UITextView时使用）

若因业务需求必须使用UITextView，可通过禁用更多不必要的交互功能来降低CPU占用：

private func addViews() {
    annotationsTextView.isScrollEnabled = false
    annotationsTextView.isEditable = false
    annotationsTextView.isSelectable = false // 禁用文本选择
    annotationsTextView.allowsEditingTextAttributes = false // 禁用富文本编辑
    annotationsTextView.textContainerInset = .zero // 重置内边距，减少布局计算
    annotationsTextView.textContainer.lineFragmentPadding = 0 // 重置行内边距
    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),
    ])
}

这些设置能减少UITextView的后台计算量，一定程度缓解CPU占用问题，但效果不如替换为UILabel显著。

内容的提问来源于stack exchange，提问作者Richard Witherspoon