快速连续多次调用 scrollToItem（at：at：animated：） 会导致 UICollectionView 中出现滚动故障

在没有看到完整代码的情况下，问题可能是由您反复调用.reloadItems(...)

如果这样做只是为了更改所选单元格的外观，则没有必要。

相反，让集合视图跟踪所选单元格（默认情况下会这样做），并让单元格根据其所选状态修改自己的外观。

例如，如果我们以这样的典型方式创建一个带有单个标签的单元格：

class SomeCell: UICollectionViewCell {
    
    static let identifier: String = "SomeCell"
    
    let theLabel: UILabel = {
        let v = UILabel()
        v.textAlignment = .center
        return v
    }()
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    func commonInit() -> Void {
        theLabel.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(theLabel)
        let g = contentView.layoutMarginsGuide
        NSLayoutConstraint.activate([
            theLabel.topAnchor.constraint(equalTo: g.topAnchor, constant: 4.0),
            theLabel.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 8.0),
            theLabel.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -8.0),
            theLabel.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -4.0),
        ])


        // default "un-selected" appearance
        contentView.layer.borderColor = UIColor(white: 0.9, alpha: 1.0).cgColor
        contentView.layer.borderWidth = 1.0
    }

    override func layoutSubviews() {
        contentView.layer.cornerRadius = contentView.bounds.height * 0.5
    }

    // the collection view will tell us whether the cell is selected or not
    //  so update the cell appearance here
    override var isSelected: Bool {
        didSet {
            contentView.backgroundColor = isSelected ? UIColor(red: 0.5, green: 1.0, blue: 0.5, alpha: 1.0) : .systemBackground
            contentView.layer.borderWidth = isSelected ? 0.0 : 1.0
        }
    }
}

我们已经覆盖了......集合视图将在需要时设置该属性，现在我们的单元格会自动更新其“已选择/未选择”外观。var isSelected: Bool

无需致电.reloadItems

使用上述单元格的水平集合视图的示例视图控制器 - 请注意，我正在创建 4 个示例标签的“重复集”（前缀为 1-4），因此我们有足够的单元格可供滚动：

class SomeViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {
    
    var collectionView: UICollectionView!
    
    var sampleTags: [String] = [
        "Pomogranate",
        "Banana, Guava, Sapota",
        "Oranges, Mosambi",
        "Apple",
        "Blueberry",
        "Pineapple",
        "Strawberry",
    ]
    var tagsData: [String] = []

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // let's create several sets of the sample tags
        //  so we have plenty of cells to scroll
        for i in 1...4 {
            sampleTags.forEach { s in
                tagsData.append("\(i): \(s)")
            }
        }
        
        let fl = UICollectionViewFlowLayout()
        fl.scrollDirection = .horizontal
        fl.estimatedItemSize = .init(width: 80.0, height: 40.0)
        
        collectionView = UICollectionView(frame: .zero, collectionViewLayout: fl)
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(collectionView)
        
        let g = view.safeAreaLayoutGuide
        NSLayoutConstraint.activate([
            collectionView.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
            collectionView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 20.0),
            collectionView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -20.0),
            collectionView.heightAnchor.constraint(equalToConstant: 50.0),
        ])
        
        collectionView.register(SomeCell.self, forCellWithReuseIdentifier: SomeCell.identifier)
        collectionView.dataSource = self
        collectionView.delegate = self
        
        collectionView.layer.borderColor = UIColor.red.cgColor
        collectionView.layer.borderWidth = 1.0
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return tagsData.count
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let c = collectionView.dequeueReusableCell(withReuseIdentifier: SomeCell.identifier, for: indexPath) as! SomeCell
        c.theLabel.text = tagsData[indexPath.item]
        return c
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        
        // scroll the selected cell to the center
        collectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: true)
        
        DispatchQueue.main.async {
            self.viewModel.fetchProductData(forPositon: indexPath)
        }
        
    }
}

编辑 - 附加要求：选择时单元格字体更改为粗体，而不会导致单元格大小更改...

最简单的方法是向单元格添加两个标签 - 一个使用粗体字体，另一个使用常规字体。

设置约束条件，使“粗体”标签控制宽度，而“常规”标签的宽度将略高于所需宽度。

选中时显示粗体标签，选中时显示常规标签。

因此，从上面略微修改了单元格类：

class SomeCell: UICollectionViewCell {
    
    static let identifier: String = "SomeCell"
    
    public var title: String = "" {
        didSet {
            theLabel.text = title
            theBoldLabel.text = title
        }
    }
    
    private let theLabel = UILabel()
    private let theBoldLabel = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    private func commonInit() -> Void {
        [theLabel, theBoldLabel].forEach { v in
            v.textAlignment = .center
            v.translatesAutoresizingMaskIntoConstraints = false
            contentView.addSubview(v)
        }
        let g = contentView.layoutMarginsGuide
        NSLayoutConstraint.activate([
            theBoldLabel.topAnchor.constraint(equalTo: g.topAnchor, constant: 4.0),
            theBoldLabel.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 8.0),
            theBoldLabel.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -8.0),
            theBoldLabel.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -4.0),

            theLabel.topAnchor.constraint(equalTo: theBoldLabel.topAnchor, constant: 0.0),
            theLabel.leadingAnchor.constraint(equalTo: theBoldLabel.leadingAnchor, constant: 0.0),
            theLabel.trailingAnchor.constraint(equalTo: theBoldLabel.trailingAnchor, constant: 0.0),
            theLabel.bottomAnchor.constraint(equalTo: theBoldLabel.bottomAnchor, constant: 0.0),
        ])
        
        theLabel.font = .systemFont(ofSize: 17.0, weight: .regular)
        theBoldLabel.font = .systemFont(ofSize: 17.0, weight: .bold)

        // not strictly necessary, but the bold label controls the sizing
        // so let's make sure it sizes correctly
        theBoldLabel.setContentHuggingPriority(.required, for: .horizontal)
        theBoldLabel.setContentCompressionResistancePriority(.required, for: .horizontal)
        
        // default "un-selected" appearance
        contentView.layer.borderColor = UIColor(white: 0.9, alpha: 1.0).cgColor
        contentView.layer.borderWidth = 1.0
        theBoldLabel.isHidden = true
    }
    
    // the collection view will tell us whether the cell is selected or not
    //  so update the cell appearance here
    override var isSelected: Bool {
        didSet {
            contentView.backgroundColor = isSelected ? UIColor(red: 0.5, green: 1.0, blue: 0.5, alpha: 1.0) : .systemBackground
            contentView.layer.borderWidth = isSelected ? 0.0 : 1.0
            theLabel.isHidden = isSelected
            theBoldLabel.isHidden = !isSelected
        }
    }
    override func layoutSubviews() {
        contentView.layer.cornerRadius = contentView.bounds.height * 0.5
    }
}

然后在控制器的 中，我们将设置单元格的属性，而不是设置“单个”标签的文本，这将在两个标签中设置相同的文本：cellForItemAttitle

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let c = collectionView.dequeueReusableCell(withReuseIdentifier: SomeCell.identifier, for: indexPath) as! SomeCell
    //c.theLabel.text = tagsData[indexPath.item]
    c.title = tagsData[indexPath.item]
    return c
}

编辑 2 - 回应有关以编程方式选择的评论...

首先，不要调用：

cell.isSelected = true

这并不能告诉集合视图单元格已被选中。

这是以编程方式选择单元格的正确方法（在本例中，我们想要选择单元格/项目并使其滚动到中心）：5

collectionView.selectItem(at: IndexPath(item: 5, section: 0), animated: true, scrollPosition: .centeredHorizontally)

请注意，以编程方式选择单元格不会调用委托函数。调用它是为了让您知道用户选择了一个单元格。didSelectItemAt

因此，如果您想以编程方式选择一个单元格，并且希望发生一些事情，请使用“执行某项操作”代码来跟进它。

例如：

let idxPath: IndexPath = IndexPath(item: 5, section: 0)
collectionView.selectItem(at: idxPath, animated: true, scrollPosition: .centeredHorizontally)
DispatchQueue.main.async {
    self.viewModel.fetchProductData(forPositon: idxPath)
}