ios - 如何使用 reloadItems 淡出项目(位于 : [indexPath])

Question

我有一个包含 uicollectionview 的 View Controller 。每个 CollectionView 单元格都包含一个按钮，单击该按钮会在单元格内添加一个新标签。为了扩展每个单元格的高度，我调用 reloadItems(at: [indexPath])。

不幸的是，调用 reloadItems(at: [indexPath]) 会淡出旧标签并淡入新标签，如何防止任何标签淡出？

每次我单击 addLabel 按钮时，该错误都会变得更加明显:一个新标签淡入，但以前不可见的任何标签突然再次出现，并且以前可见的任何标签都神奇地变成了又看不见了。

reloadItems(at: [indexPath]) 似乎以不同的方式切换每个新标签的 alpha。我想调整单元格大小并向单元格添加新标签，而不会让任何标签消失。

这是我的代码:

View Controller

class ViewController: UIViewController {

weak var collectionView: UICollectionView!
var expandedCellIdentifier = "ExpandableCell"

var cellWidth:CGFloat{
    return collectionView.frame.size.width
}
var expandedHeight : CGFloat = 200
var notExpandedHeight : CGFloat = 50    

//the first Int gives the row, the second Int gives the amount of labels in the row
var isExpanded = [Int:Int]()

override func viewDidLoad() {
    super.viewDidLoad()
    for i in 0..<4 {
        isExpanded[i] = 1
    }
  }
}


extension ViewController:UICollectionViewDataSource{
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return isExpanded.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: expandedCellIdentifier, for: indexPath) as! ExpandableCell
    cell.indexPath = indexPath
    cell.delegate = self
    cell.setupCell = "true"
    return cell

}
}

extension ViewController:UICollectionViewDelegateFlowLayout{
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    if isExpanded[indexPath.row]! > 1{

        let height = (collectionView.frame.width/10)
        let newHeight = height * CGFloat(isExpanded[indexPath.row]!)
        return CGSize(width: cellWidth, height: newHeight)

    }else{
        return CGSize(width: cellWidth, height: collectionView.frame.width/6 )
    }

  }

}

extension ViewController:ExpandedCellDeleg{
func topButtonTouched(indexPath: IndexPath) {
    isExpanded[indexPath.row] = isExpanded[indexPath.row]! + 1

    UIView.animate(withDuration: 0.8, delay: 0.0, usingSpringWithDamping: 0.9, initialSpringVelocity: 0.9, options: UIView.AnimationOptions.curveEaseInOut, animations: {
        self.collectionView.reloadItems(at: [indexPath])
    }, completion: { success in
        print("success")
    })
  }
}

协议(protocol)

protocol ExpandedCellDeleg:NSObjectProtocol{
func topButtonTouched(indexPath:IndexPath)
}

可扩展单元格

class ExpandableCell: UICollectionViewCell {

weak var delegate:ExpandedCellDeleg?
public var amountOfIntervals:Int = 1

public var indexPath:IndexPath!

var setupCell: String? {
    didSet {
        print("cell should be setup!!")
    }
}

let ivAddLabel: UIImageView = {
    let imageView = UIImageView()
    imageView.translatesAutoresizingMaskIntoConstraints = false
    imageView.image = #imageLiteral(resourceName: "plus")
    imageView.tintColor = .black
    imageView.contentMode = .scaleToFill
    imageView.backgroundColor = UIColor.clear
    return imageView
}()

override init(frame: CGRect) {
    super.init(frame: .zero)

    contentView.addSubview(ivAddLabel)

    let name = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 18))
    name.center = CGPoint(x: Int(frame.width)/2 , y: 20)
    name.textAlignment = .center
    name.font = UIFont.systemFont(ofSize: 16)
    name.textColor = UIColor.black
    name.text = "Fred"
    contentView.addSubview(name)

    ivAddLabel.rightAnchor.constraint(equalTo: self.rightAnchor, constant: -14).isActive = true
    ivAddLabel.topAnchor.constraint(equalTo: self.topAnchor, constant: 10).isActive = true
    ivAddLabel.widthAnchor.constraint(equalToConstant: 20).isActive = true
    ivAddLabel.heightAnchor.constraint(equalToConstant: 20).isActive = true
    ivAddLabel.layer.masksToBounds = true
    ivAddLabel.isUserInteractionEnabled = true
    let addGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(ivAddLabelSelected))
    ivAddLabel.addGestureRecognizer(addGestureRecognizer)
}
required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}
@objc func ivAddLabelSelected(){
    print("add button was tapped!")
    if let delegate = self.delegate{

        amountOfIntervals = amountOfIntervals + 1
        let height = (20*amountOfIntervals)

        let name = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 18))
        name.center = CGPoint(x: Int(frame.width)/2, y: height)
        name.textAlignment = .center
        name.font = UIFont.systemFont(ofSize: 16)
        name.textColor = UIColor.black
        name.text = "newFred"
        name.alpha = 0.0
        contentView.addSubview(name)
        UIView.animate(withDuration: 0.2, animations: { name.alpha = 1.0 })

        delegate.topButtonTouched(indexPath: indexPath)
    }
  }
}

Answer 1

这是因为您为新标签设置了动画

UIView.animate(withDuration: 0.2, animations: { name.alpha = 1.0 })

并行地重新加载单元格，该单元格创建一个新单元格/重用现有单元格并显示它，而且您还将重新加载包装到动画 block 中，这看起来很奇怪且无用:

UIView.animate(withDuration: 0.8, delay: 0.0, usingSpringWithDamping: 0.9, initialSpringVelocity: 0.9, options: UIView.AnimationOptions.curveEaseInOut, animations: {
        self.collectionView.reloadItems(at: [indexPath])
    }, completion: { success in
        print("success")
    })

您需要删除两个动画并重新加载单元格。如果您需要一个漂亮的单元格扩展动画，您需要实现集合布局，它将处理所有状态 - 动画的开始、中间、结束。这个很难(硬。

尝试使用其他答案“UICollectionView Self Sizing Cells with Auto Layout”中的建议，如果没有帮助，那么要么忘记动画的想法，要么实现自定义布局。