UICollectionView didSelectItemAt（）并根据状态添加/删除视图

Question

我想在选定的单元格中添加复选标记。如果随后取消选择该单元格（因此选择了另一个单元格），我想删除复选标记。顶部图像视图独立于集合视图，表示用户相机胶卷中的选定单元格。集合视图的数据源是从PHAssets获取的图像列表。

问题是，如果我不在indexPath重新加载项目，则取消选择的单元格复选标记不会被删除。此外，如果我滚动浏览集合视图，我会看到来自我甚至没有点击的单元格的随机复选标记。我假设它与重复使用细胞有关。有人可以帮帮我吗？

以下是来自视图控制器和单元格的代码片段......

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: photoCellReuseIdentifier, for: indexPath) as? PhotosCell else { fatalError("Couldn't return a photo cell") }
    let requestOptions = PHImageRequestOptions()
    requestOptions.isSynchronous = true
    requestOptions.isNetworkAccessAllowed = true
    requestOptions.deliveryMode = .highQualityFormat

    photoManager.requestImage(for: photoAssets![indexPath.row], targetSize: CGSize(width: 100, height: 100), contentMode: .aspectFill, options: requestOptions, resultHandler: { (image, nil) in
        cell.photoView.image = image
    })

    if cell.isSelected {
        cell.setupCheckmarkBanner()
    }
    else {
        cell.removeCheckmarkBanner()
    }

    if indexPath.row == 0 && self.isFirstLoad {
        self.selectedImageView.image = cell.photoView.image
        collectionView.selectItem(at: indexPath, animated: false, scrollPosition: UICollectionViewScrollPosition.bottom)
        cell.setupCheckmarkBanner()
        self.isFirstLoad = false
    }


    return cell
}

func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
    previousIndexPath = indexPath
    collectionView.reloadItems(at: [indexPath])
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    if previousIndexPath != indexPath {
        collectionView.reloadItems(at: [indexPath])
        guard let cell = collectionView.cellForItem(at: indexPath) as? PhotosCell else { fatalError("Couldn't return a photo cell") }
        selectedImageView.image = cell.photoView.image
    }
}


class PhotosCell: UICollectionViewCell {

let photoView = UIImageView()
var checkmarkBannerImageView: UIImageView? 

override init(frame: CGRect) {
    super.init(frame: frame)
    addSubview(photoView)
    photoView.anchor(top: topAnchor, left: leadingAnchor, bottom: bottomAnchor, right: trailingAnchor, paddingTop: 0, paddingLeft: 0, paddingBottom: 0, paddingRight: 0, width: 0, height: 0)
}

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

func setupCheckmarkBanner() {
    checkmarkBannerImageView = UIImageView(image: #imageLiteral(resourceName: "check").withRenderingMode(.alwaysTemplate))
    checkmarkBannerImageView?.contentMode = .center
    checkmarkBannerImageView?.contentScaleFactor = 4.0
    checkmarkBannerImageView?.tintColor = .white
    checkmarkBannerImageView?.setBottomBorder(for: .white)
    checkmarkBannerImageView?.convertToCircle(value: 12)

    photoView.addSubview(checkmarkBannerImageView!)
    checkmarkBannerImageView?.anchor(top: photoView.topAnchor, left: nil, bottom: nil, right: photoView.trailingAnchor, paddingTop: 4, paddingLeft: 0, paddingBottom: 0, paddingRight: 4, width: 24, height: 24)
}

func removeCheckmarkBanner() {
    checkmarkBannerImageView?.removeFromSuperview()
    checkmarkBannerImageView?.constraints.forEach{$0.isActive = false }
    checkmarkBannerImageView = nil
}
}

Answer 1

你必须保存所选单元格的索引路径（在DidSelect和DidDescelect期间创建一个属性并进行分配，并在cellForRow期间检查索引路径是否相同，如果是，请勾选复选标记，如果不是，则删除复选标记。 这样当重新使用单元格时，ui设置将被刷新。

此外，在取消选择/选择期间，仅对已更改的行执行reloadCellAtIndexPath / reloadItems以避免再次重新加载所有单元格。

编辑：

好吧，我要改变的第一件事是，你在photoManager.requestImage块中的所有逻辑我都会移到外面，因为这可能是异步方法。 其次，你应该在每个单元格中设置或删除复选标记，因为当它被重用时，会调用此方法。

这只是一个例子：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: photoCellReuseIdentifier, for: indexPath) as? PhotosCell else { fatalError("Couldn't return a photo cell") }
    let requestOptions = PHImageRequestOptions()
    requestOptions.isSynchronous = true
    requestOptions.isNetworkAccessAllowed = true
    requestOptions.deliveryMode = .highQualityFormat

    photoManager.requestImage(for: photoAssets![indexPath.row], targetSize: CGSize(width: 100, height: 100), contentMode: .aspectFill, options: requestOptions, resultHandler: { (image, nil) in
        cell.photoView.image = image
        if indexPath.row == 0 && self.isFirstLoad {
            self.selectedImageView.image = image
        }
    })

    if indexPath.row == 0 && self.isFirstLoad {
            collectionView.selectItem(at: indexPath, animated: false, scrollPosition: UICollectionViewScrollPosition.bottom)
            self.isFirstLoad = false
        }

    if cell.isSelected { // dont remember if this is the correct method
        cell.setupCheckmarkBanner()
    } else {
        cell.removeCheckmarkBanner()
    }

    return cell
}

Answer 2

为了避免重用单元格中不需要的内容，您可以覆盖prepareForReuse（）方法，并在那里执行所有设置工作（例如隐藏复选标记）

Answer 3

我明白了！它必须在出列后完成......

import UIKit
import Photos

class PhotosViewController: UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource {

let selectedImageView = UIImageView()
var photoAssets: PHFetchResult<PHAsset>?
let photoManager = PHImageManager.default()
var selectedIndexPath: IndexPath = IndexPath(row: 0, section: 0)

let collectionView: UICollectionView = {
    let collectionViewFlowLayout = UICollectionViewFlowLayout()
    collectionViewFlowLayout.sectionInset = UIEdgeInsetsMake(0, 2, 0, 2)
    collectionViewFlowLayout.minimumInteritemSpacing = 0
    collectionViewFlowLayout.minimumLineSpacing = 2
    let collectionView = UICollectionView(frame: .zero, collectionViewLayout: collectionViewFlowLayout)
    collectionView.backgroundColor = .white
    return collectionView
}()

private let photoCellReuseIdentifier = "photoCell"
var photos = [UIImage]()

override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .white
    view.addSubview(selectedImageView)
    view.addSubview(collectionView)
    collectionView.dataSource = self
    collectionView.delegate = self
    fetchAssets()
    selectedImageView.anchor(top: view.topAnchor, left: view.leadingAnchor, bottom: collectionView.topAnchor, right: view.trailingAnchor, paddingTop: 0, paddingLeft: 2, paddingBottom: 2, paddingRight: 2, width: 0, height: view.bounds.height/1.5)
    collectionView.anchor(top: nil, left: view.leadingAnchor, bottom: view.bottomAnchor, right: view.trailingAnchor, paddingTop: 5, paddingLeft: 0, paddingBottom: 0, paddingRight: 0, width: 0, height: 0)
    collectionView.register(PhotosCell.self, forCellWithReuseIdentifier: photoCellReuseIdentifier)
 }

private func fetchAssets() {
    guard let cameraRollPhotoCollection = PHAssetCollection.fetchAssetCollections(with: .smartAlbum, subtype: .smartAlbumUserLibrary, options: nil).firstObject else { return }
    let assetOptions = PHFetchOptions()
    let sortDescriptor = NSSortDescriptor(key: "creationDate", ascending: false)
    assetOptions.sortDescriptors = [sortDescriptor]
    photoAssets = PHAsset.fetchAssets(in: cameraRollPhotoCollection, options: assetOptions)

    let requestOptions = PHImageRequestOptions()
    requestOptions.isSynchronous = true
    requestOptions.isNetworkAccessAllowed = true
    requestOptions.deliveryMode = .highQualityFormat

    guard let photoAssets = photoAssets else { return }
    let photoAssetsCount = photoAssets.count - 1

    for assetIndex in 0..<photoAssetsCount {
    photoManager.requestImage(for: photoAssets[assetIndex], targetSize: CGSize(width: 100, height: 100), contentMode: .aspectFill, options: requestOptions, resultHandler: { (image, nil) in
        guard let image = image else { return }
        self.photos.append(image)
    })

    }

}

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

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return photos.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: photoCellReuseIdentifier, for: indexPath) as? PhotosCell else { fatalError("Couldn't return a photo cell") }
    cell.photoView.image = photos[indexPath.row]
    if indexPath == selectedIndexPath {
        cell.setupCheckmarkBanner()
    }
    else {
        cell.removeCheckmarkBanner()
    }

    return cell
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let width = view.bounds.size.width/3 - 3
    let height = view.bounds.size.height/5
    return CGSize(width: width, height: height)
}

func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
    if collectionView.indexPathsForVisibleItems.contains(indexPath) {
        guard let deselectedCell = collectionView.cellForItem(at: indexPath) as? PhotosCell else { fatalError("Couldn't return a photo cell") }
        deselectedCell.removeCheckmarkBanner()
    }
    else {
        collectionView.deselectItem(at: indexPath, animated: false)
    }
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    guard let selectedCell = collectionView.cellForItem(at: indexPath) as? PhotosCell else { fatalError("Couldn't return a photo cell") }
    selectedIndexPath = indexPath
    selectedCell.setupCheckmarkBanner()
}

}

扩展名PhotosViewController：ImageDismissalDelegate {     func sendProfilePictureImage（图片：UIImage）{

}

}