swift-将数据传递给UICollectionViewCell的正确方法

Question

我正在尝试创建自己的Book应用，并使用UICollectionView列出所有图书。每个单元格的数据都来自.plist文件，我正在使用自定义flowLayout（稍后再进行一些更改）。

所以现在我在滚动时会陷入延迟和滞后。我想我在将数据传递到单元格或单元格初始化时犯了错误。

.xib和自定义类创建的单元格，只有一些布局和UI：

class BookCoverCell: UICollectionViewCell {
    @IBOutlet weak var view1: UIView!
    @IBOutlet weak var view2: UIView!
    @IBOutlet weak var imageView: UIImageView!
    @IBOutlet weak var darkRedView: UIView!
    @IBOutlet weak var lightRedView: UIView!
    @IBOutlet weak var readButton: UIButton!
    @IBOutlet weak var pageLabel: UILabel!    


    override func awakeFromNib() {
        super.awakeFromNib()
        clipsToBounds = true
        self.backgroundColor = UIColor(white: 1, alpha: 0.0)
        view1.layer.cornerRadius = 10
        view2.layer.cornerRadius = 10
        darkRedView.layer.cornerRadius = 10
        lightRedView.layer.cornerRadius = 10
    }    
} 

在ViewController的课程：

class MainVC: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UIScrollViewDelegate {


    @IBOutlet weak var collectionContainerView: UIView!
    @IBOutlet weak var collectionView: UICollectionView!

    var books: Array<Book>? {
        didSet {
            collectionView.reloadData()
        }
    }
    var flowLayout = UICollectionViewFlowLayout()
    override func viewDidLayoutSubviews() {        
        flowLayout = ZoomAndSnapFlowLayout()
        collectionView.collectionViewLayout = flowLayout
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionContainerView.backgroundColor = UIColor(white: 1, alpha: 0.0)
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.register(UINib(nibName: "BookCoverCell", bundle: nil), forCellWithReuseIdentifier: "BookCoverCell");
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(true)
        books = BookStore.sharedInstance.loadBooks(plist: "Books")        
    }

//MARK: UICollectionViewDelegate

    func numberOfSections(in collectionView: UICollectionView) -> Int {
      return 1
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        if let books = books {
            return books.count
        }
        return 0
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "BookCoverCell", for: indexPath) as! BookCoverCell
        let book = books![indexPath.row]
        let cover = book.coverImage()!
        let color = book.getDominantColor()
        cell.view1.backgroundColor = color
        cell.imageView.image = cover
        cell.pageLabel.text = "Pages: 29"
        cell.readButton.setTitle("Read", for: .normal)
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let book = books?[indexPath.row]
        print ("open")
    }

}

我的布局现在看起来像：

class ZoomAndSnapFlowLayout: UICollectionViewFlowLayout {


    var cellWidth = CGFloat()
    var cellHeight = CGFloat()
    var minLineSpacing = CGFloat()

    override init() {
        super.init()
        self.scrollDirection = .horizontal
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func prepare() {
        guard let collectionView = collectionView else { fatalError() }

        cellHeight = collectionView.frame.height * 0.8
        minLineSpacing = 200
        cellWidth = cellHeight

        itemSize = CGSize(width: cellWidth, height: cellHeight)

        let verticalInsets = (collectionView.frame.height - collectionView.adjustedContentInset.top - collectionView.adjustedContentInset.bottom - itemSize.height) / 2
        let horizontalInsets = (collectionView.frame.width - collectionView.adjustedContentInset.right - collectionView.adjustedContentInset.left - itemSize.width) / 2

        sectionInset = UIEdgeInsets(top: verticalInsets, left: horizontalInsets, bottom: verticalInsets, right: horizontalInsets)

        super.prepare()
    }
}

所以我很确定代码中有一些错误，但是找不到它们（（任何建议对我都会有帮助！

UPDATE：首先，谢谢！我已经更改了代码，并用最小的图像替换了一个很大的图像，并且现在可以将主导颜色简单地变为白色，并且功能已经变得更好了！

BUT第一次滚动开始时，只有一个第一和第二个单元格，当它们滚动到屏幕的左边缘时，延迟或延迟很小。然后，所有单元都在两个方向（左/右）上滚动，没有滞后，甚至前两个也没有滞后。

现在我的代码如下：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "BookCoverCell", for: indexPath) as! BookCoverCell
        let book = books![indexPath.row]
        let cover = UIImage(named: "flag.png")
        let color = #colorLiteral(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
        cell.view1.backgroundColor = color
        cell.imageView.image = cover
        cell.pageLabel.text = "Pages: 29"
        cell.readButton.setTitle("Read", for: .normal)
        return cell
    }

和UPDATE＃2删除

flowLayout = ZoomAndSnapFlowLayout()
collectionView.collectionViewLayout = flowLayout

为了viewWillAppear()也解决这些小延迟！！万岁！）

Answer 1

阅读有关时间剖析和收集视图的本文：https://voxels.github.io/eliminating-collection-view-tearing-with-xcode-time-profiler-instrument

由于您的实现非常简单，所以不会有很多错误的事情，但是您可能会遇到与本文作者相同的问题-图像本身非常大，需要阅读和调整大小。

他们通过制作适当尺寸的图像解决了这个问题。

在您的情况下，getDominantColor在大图像上也会变慢（我假设它读取像素来获得主要颜色。您还应该考虑缓存该颜色，而不是每次都重新计算（如果您尚未这样做） ）。