swift - 使用 didSelect 方法在 viewDidLoad 后在 Cell 中显示图像

Question

我有一个单元格，其中包含一个空的 UIImageView 和一个嵌套在包含一行图像的 collectionView 中。我创建了一个 didSelect 函数，我想突出显示所选行并在空 UIImageView 中显示它的图像。

我尝试了 reloadData 函数，但应用程序崩溃了。我在没有 reloadData 函数的情况下尝试了它，并且索引路径的项目仅突出显示。

class DisplayImageCell: UICollectionViewCell, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    private let displayCell = "DisplayImageCell"

    let imageContainer: UIImageView = {
        let imageContainer = UIImageView()
        imageContainer.clipsToBounds = true
        imageContainer.backgroundColor = UIColor(patternImage: (UIImage(imageLiteralResourceName: "ic_person_outline_white_2x").withRenderingMode(.alwaysTemplate)))
        imageContainer.isUserInteractionEnabled = true
        imageContainer.translatesAutoresizingMaskIntoConstraints = false
        return imageContainer
    }()

    let pictureCollection: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 5
        layout.minimumInteritemSpacing = 10
        let imageContainer = UICollectionView(frame: .zero, collectionViewLayout: layout)
        imageContainer.showsHorizontalScrollIndicator = false
        imageContainer.clipsToBounds = true
        imageContainer.tintColor = .yellow
        imageContainer.isUserInteractionEnabled = true
        imageContainer.translatesAutoresizingMaskIntoConstraints = false
        return imageContainer
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear

        pictureCollection.dataSource = self
        pictureCollection.delegate = self
        pictureCollection.register(ImageCell.self, forCellWithReuseIdentifier: displayCell)

        addSubview(imageContainer)
        NSLayoutConstraint.activate([
            imageContainer.topAnchor.constraint(equalTo: topAnchor),
            imageContainer.heightAnchor.constraint(equalTo: heightAnchor, multiplier: 0.80),
            imageContainer.widthAnchor.constraint(equalTo: widthAnchor)
            ])

        addSubview(pictureCollection)
        NSLayoutConstraint.activate([
            pictureCollection.topAnchor.constraint(equalTo: imageContainer.bottomAnchor, constant: 10),
            pictureCollection.bottomAnchor.constraint(equalTo: bottomAnchor),
            pictureCollection.widthAnchor.constraint(equalTo: widthAnchor)
            ])

    }

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

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 7
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: displayCell, for: indexPath) as! ImageCell
        let imageOption = ImageOption(rawValue: indexPath.row)
        cell.iconImageView.image = imageOption?.icon()
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: pictureCollection.frame.height, height: pictureCollection.frame.height)
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        updateCell(having: indexPath, selected: true)
    }

    func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
        updateCell(having: indexPath, selected: false)
    }

    func collectionView(_ collectionView: UICollectionView, didHighlightItemAt indexPath: IndexPath) {
        updateCell(having: indexPath, selected: true)
    }

    func collectionView(_ collectionView: UICollectionView, didUnhighlightItemAt indexPath: IndexPath) {
        updateCell(having: indexPath, selected: false)
    }

    private class ImageCell: UICollectionViewCell {

        let iconImageView: UIImageView = {
            let iv = UIImageView()
            iv.contentMode = .scaleAspectFit
            iv.clipsToBounds = true
            iv.translatesAutoresizingMaskIntoConstraints = false
            iv.isUserInteractionEnabled = true
            return iv
        }()

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

            backgroundColor = .blue

            addSubview(iconImageView)
            NSLayoutConstraint.activate([
                iconImageView.heightAnchor.constraint(equalTo: heightAnchor),
                iconImageView.widthAnchor.constraint(equalTo: widthAnchor),
                iconImageView.centerXAnchor.constraint(equalTo: centerXAnchor),
                iconImageView.centerYAnchor.constraint(equalTo: centerYAnchor)
                ])

        }

        required init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
    }
    func updateCell(having indexPath: IndexPath, selected: Bool) {

        let selectedBackgroundColor = UIColor(red: 41/255.0, green: 211/255.0, blue: 241/255.0, alpha: 1.0)
        let defaultBackgroundColor = UIColor.blue
        let imageSlot = DisplayImageCell()
        let ep = EditProfileController()

        if let cell = pictureCollection.cellForItem(at: indexPath) {
            cell.contentView.backgroundColor = selected ? selectedBackgroundColor : defaultBackgroundColor
            imageSlot.imageContainer.image = UIImage(named: "ThumbsUp")
            ep.collectionView.reloadData()
        }
    }
}

预期的结果是空 ImageView 显示所选indexPath.row的图像。当我尝试重新加载 collectionView 时，发现一个 nil 值的 fatal error 。

Answer 1

如果您想在 imageContainer 中显示 Collection View 的数据源中选定的图像，您只需在 didSelectItemAt indexPath 中获取图像，就像在cellForItemAt indexPath:

let imageOption = ImageOption(rawValue: indexPath.item)

然后

imageContainer.image = imageOption?.icon()

实际上没有必要调用reloadData()，因为 Collection View 的数据源尚未更新。