根据你的另一个问题，我猜你正在尝试做这样的事情......
显示设备照片中的图像，并允许多个选择按顺序：
并且，当您取消选择一个单元格时 - 例如，取消选择我的第二个选择 - 您想要重新编号剩余的选择：
要做到这一点，您需要跟踪数组中的单元格选择 - 因为它们是被制作的 - 这样您就可以保持编号。
有几种方法可以解决这个问题……这里有一个。
首先，我建议将您的count 属性重命名为index，并在设置值时显示或隐藏overlay：
var index: Int = 0 {
didSet {
overlay.countLabel.text = "\(index)"
// hide if count is Zero, show if not
overlay.isHidden = index == 0
}
}
当您从cellForItemAt 中取出一个单元格时，查看 indexPath 是否在我们的“跟踪”数组中并适当地设置单元格的.index 属性（这也将显示/隐藏覆盖）。
接下来，当您选择一个单元格时：
- 将
indexPath 添加到我们的跟踪数组中
- 我们可以设置
.index 属性 - 使用我们的跟踪数组的计数 - 直接更新单元格的外观，因为它不会影响任何其他单元格
当您取消选择一个单元格时，我们必须做额外的工作：
- 从我们的跟踪数组中删除 indexPath
- 重新加载单元格以便重新编号
这是一个完整的示例 - 代码中有很多 cmets。
圆形视图
class CircleView: UIView {
// simple view subclass that keeps itself "round"
// (assuming it has a 1:1 ratio)
override func layoutSubviews() {
layer.cornerRadius = bounds.width * 0.5
}
}
CustomAssetCellOverlay
class CustomAssetCellOverlay: UIView {
lazy var circleView: CircleView = {
let view = CircleView()
view.backgroundColor = UIColor(red: 0.0, green: 0.5, blue: 1.0, alpha: 1.0)
view.translatesAutoresizingMaskIntoConstraints = false
return view
}()
lazy var countLabel: UILabel = {
let label = UILabel()
let font = UIFont.preferredFont(forTextStyle: .headline)
label.font = UIFont.systemFont(ofSize: font.pointSize, weight: UIFont.Weight.bold)
label.textAlignment = .center
label.textColor = .white
label.adjustsFontSizeToFitWidth = true
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
private func setup(){addSubview(circleView)
addSubview(circleView)
addSubview(countLabel)
NSLayoutConstraint.activate([
// circle view at top-left
circleView.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 4.0),
circleView.topAnchor.constraint(equalTo: topAnchor, constant: 4.0),
// circle view Width: 28 Height: 1:1 ratio
circleView.widthAnchor.constraint(equalToConstant: 28.0),
circleView.heightAnchor.constraint(equalTo: circleView.widthAnchor),
// count label constrained ot circle view
countLabel.leadingAnchor.constraint(equalTo: circleView.leadingAnchor),
countLabel.trailingAnchor.constraint(equalTo: circleView.trailingAnchor),
countLabel.topAnchor.constraint(equalTo: circleView.topAnchor),
countLabel.bottomAnchor.constraint(equalTo: circleView.bottomAnchor),
])
}
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
}
TestCVCell
class TestCVCell: UICollectionViewCell {
var imageView = UIImageView()
var index: Int = 0 {
didSet {
overlay.countLabel.text = "\(index)"
// hide if count is Zero, show if not
overlay.isHidden = index == 0
}
}
let overlay: CustomAssetCellOverlay = {
let view = CustomAssetCellOverlay()
view.backgroundColor = UIColor.black.withAlphaComponent(0.4)
view.isHidden = true
return view
}()
override init(frame: CGRect) {
super.init(frame: frame)
imageView.contentMode = .scaleAspectFill
imageView.clipsToBounds = true
contentView.addSubview(imageView)
contentView.addSubview(overlay)
imageView.translatesAutoresizingMaskIntoConstraints = false
overlay.translatesAutoresizingMaskIntoConstraints = false
// constrain both image view and overlay to full contentView
NSLayoutConstraint.activate([
imageView.topAnchor.constraint(equalTo: contentView.topAnchor),
imageView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
imageView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),
imageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
overlay.topAnchor.constraint(equalTo: imageView.topAnchor),
overlay.bottomAnchor.constraint(equalTo: imageView.bottomAnchor),
overlay.leadingAnchor.constraint(equalTo: imageView.leadingAnchor),
overlay.trailingAnchor.constraint(equalTo: imageView.trailingAnchor),
])
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
TrackSelectionsViewController
class TrackSelectionsViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, UINavigationControllerDelegate {
var myCollectionView: UICollectionView!
// array to track selected cells in the order they are selected
var selectedCells: [IndexPath] = []
// to load assests when needed
let imgManager = PHImageManager.default()
let requestOptions = PHImageRequestOptions()
// will be used to get photos data
var fetchResult: PHFetchResult<PHAsset>!
override func viewDidLoad() {
super.viewDidLoad()
// set main view background color to a nice medium blue
view.backgroundColor = UIColor(red: 0.25, green: 0.5, blue: 1.0, alpha: 1.0)
// request Options to be used in cellForItemAt
requestOptions.isSynchronous = false
requestOptions.deliveryMode = .opportunistic
// vertical stack view for the full screen (safe area)
let mainStack = UIStackView()
mainStack.axis = .vertical
mainStack.spacing = 0
mainStack.translatesAutoresizingMaskIntoConstraints = false
// add it to the view
view.addSubview(mainStack)
let g = view.safeAreaLayoutGuide
NSLayoutConstraint.activate([
mainStack.topAnchor.constraint(equalTo: g.topAnchor, constant:0.0),
mainStack.leadingAnchor.constraint(equalTo: g.leadingAnchor),
mainStack.trailingAnchor.constraint(equalTo: g.trailingAnchor),
mainStack.bottomAnchor.constraint(equalTo: g.bottomAnchor),
])
// create a label
let label = UILabel()
// add the label to the main stack view
mainStack.addArrangedSubview(label)
// label properties
label.textColor = .white
label.textAlignment = .center
label.text = "Select Photos"
label.heightAnchor.constraint(equalToConstant: 48.0).isActive = true
// setup the collection view
setupCollection()
// add it to the main stack view
mainStack.addArrangedSubview(myCollectionView)
// start the async call to get the assets
grabPhotos()
}
func setupCollection() {
let layout = UICollectionViewFlowLayout()
myCollectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
myCollectionView.delegate = self
myCollectionView.dataSource = self
myCollectionView.backgroundColor = UIColor.white
myCollectionView.allowsMultipleSelection = true
myCollectionView.register(TestCVCell.self, forCellWithReuseIdentifier: "cvCell")
}
//MARK: CollectionView
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
if let cell = collectionView.cellForItem(at: indexPath) as? TestCVCell {
// add newly selected cell (index path) to our tracking array
selectedCells.append(indexPath)
// when selecting a cell,
// we can update the appearance of the newly selected cell
// directly, because it won't affect any other cells
cell.index = selectedCells.count
}
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
// when de-selecting a cell,
// we can't update the appearance of the cell directly
// because if it's not the last cell selected, the other
// selected cells need to be re-numbered
// get the index of the deselected cell from our tracking array
guard let idx = selectedCells.firstIndex(of: indexPath) else { return }
// remove from our tracking array
selectedCells.remove(at: idx)
// reloadData() clears the collection view's selected cells, so
// get a copy of currently selected cells
let curSelected: [IndexPath] = collectionView.indexPathsForSelectedItems ?? []
// reload collection view
// we do this to update all cells' appearance,
// including re-numbering the currently selected cells
collectionView.reloadData()
// save current Y scroll offset
let saveY = collectionView.contentOffset.y
collectionView.performBatchUpdates({
// re-select previously selected cells
curSelected.forEach { pth in
collectionView.selectItem(at: pth, animated: false, scrollPosition: .centeredVertically)
}
}, completion: { _ in
// reset Y offset
collectionView.contentOffset.y = saveY
})
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
guard fetchResult != nil else { return 0 }
return fetchResult.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cvCell", for: indexPath) as! TestCVCell
imgManager.requestImage(for: fetchResult.object(at: indexPath.item) as PHAsset, targetSize: CGSize(width:120, height: 120),contentMode: .aspectFill, options: requestOptions, resultHandler: { (image, error) in
cell.imageView.image = image
})
// get the index of this indexPath from our tracking array
// if it's not there (nil), set it to -1
let idx = selectedCells.firstIndex(of: indexPath) ?? -1
// set .count property to index + 1 (arrays are zero-based)
cell.index = idx + 1
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
let width = collectionView.frame.width
return CGSize(width: width/4 - 1, height: width/4 - 1)
}
override func viewWillLayoutSubviews() {
super.viewWillLayoutSubviews()
myCollectionView.collectionViewLayout.invalidateLayout()
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 1.0
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return 1.0
}
//MARK: grab photos
func grabPhotos(){
DispatchQueue.global(qos: .background).async {
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key:"creationDate", ascending: false)]
self.fetchResult = PHAsset.fetchAssets(with: .image, options: fetchOptions)
if self.fetchResult.count == 0 {
print("No photos found.")
}
DispatchQueue.main.async {
self.myCollectionView.reloadData()
}
}
}
}
注意：这只是示例代码！！！不应将其视为“生产就绪”。