在 reloadData() 之后重绘 UICollectionViewCell 失败

Question

我有一个 UICollectionViewCell：

"Gradient View" 是一个具有渐变的 UIView:

数据来源是CoreData。在集合视图中，我有对 CoreData 进行排序的按钮：

@IBAction func allMealsBtn(_ sender: Any) {
    let fetchRequest: NSFetchRequest<Meal> = Meal.fetchRequest()
    let dateSort = NSSortDescriptor(key: "created", ascending: false)
    fetchRequest.sortDescriptors = [dateSort]

    let controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)

    controller.delegate = self
    self.controller = controller

    do {
        try controller.performFetch()
    } catch {
        let error = error as NSError
        print("Couldn't fetch data from CoreData with error: \(error.debugDescription)")
    }
    collectionView.reloadData()

}

按下排序按钮后，集合视图会重新加载并显示正确的数据。但是，渐变视图成倍增加，就好像单元格没有被破坏一样。这是我多次排序数据后看到的：

如何确保我的单元格是从头开始重新绘制的？

编辑：

我的自定义单元格class。所以在configureCell中我要检查我的gradientView是否添加到视图中，如果是，则添加渐变，如果没有，添加，并添加渐变。我该如何做这项检查？

class 集合单元格：UICollectionViewCell {

@IBOutlet weak var mealImg: UIImageView!
@IBOutlet weak var mealTitleLbl: UILabel!
@IBOutlet weak var gradientView: UIView!

func configureCell(meal: Meal) {
    mealTitleLbl.text = meal.title

    let img = meal.getMealImage()
    mealImg.image = img

    gradientView.addGradientWithColor(color: UIColor.clear)

    // How can I check if my gradientView is added to the view, if yes, then add gradient, if not, add it, and only then add gradient.

}

override func prepareForReuse() {
    super.prepareForReuse()

    gradientView.removeFromSuperview()
}
}

extension UIView {
func addGradientWithColor(color: UIColor) {
    let gradient = CAGradientLayer()
    gradient.frame = self.bounds
    let topColor = UIColor(red:0.07, green:0.07, blue:0.07, alpha:1)
    gradient.colors = [topColor.cgColor, color.cgColor]

    self.layer.insertSublayer(gradient, at: 0)
}
}

编辑： 我放弃了扩展并实现了标志逻辑。但是，删除视图后，它在执行搜索后永远不会重新出现在单元格中。有什么想法吗？

class CollectionCell: UICollectionViewCell {

@IBOutlet weak var mealImg: UIImageView!
@IBOutlet weak var mealTitleLbl: UILabel!
@IBOutlet weak var gradientView: UIView!

var isGradientAdded = false

func configureCell(meal: Meal) {
    mealTitleLbl.text = meal.title

    let img = meal.getMealImage()
    mealImg.image = img

    if isGradientAdded == false {
        addGradient()
        isGradientAdded = true
    }
}

override func prepareForReuse() {
    super.prepareForReuse()

    gradientView.removeFromSuperview()
}

  func addGradient () {
    let gradient = CAGradientLayer()
    gradient.frame = gradientView.bounds
    let topColor = UIColor(red:0.07, green:0.07, blue:0.07, alpha:1)
    let botomColor = UIColor.clear
    gradient.colors = [topColor.cgColor, botomColor.cgColor]
    gradientView.layer.insertSublayer(gradient, at: 0)
}
}

Answer 1

在 UICollectionViewCell subclass (Cell) 中，您应该覆盖 prepeareForReuse 函数 - 将单元格转换为默认模式。

如果您没有 Cell 的自定义 class - 之前创建它并在界面生成器中将其分配为 class 用于您的 Cell 单元格（以及当然不要忘记奥特莱斯）

override func prepareForReuse() {
    super.prepareForReuse()

    //set cell to initial state here 
    //e.g try to remove you gradient view  
    yourGradientView.removeFromSuperview()
}

在 reloadData() 之后重绘 UICollectionViewCell 失败

Fail to redraw UICollectionViewCell after reloadData()

core-data

ios

uicollectionview

uicollectionviewcell

swift