swift - 将 CALayer 作为子层添加到 UIImage 时出现意外行为

Question

我有带有自定义单元格的 tableView。每个单元格都有属性“名称”和“图像”。我想要做的是在图像周围添加边框。这部分有效。但是当我尝试将 backgroundColor 添加到 CALayer 时，我在 tableView 中看到的只是没有 UIImage 的 CALayer。

这里是用于更好理解的代码和设置背景颜色的示例。

 @IBOutlet weak var channelImage: UIImageView! {
        didSet {
            let borderLayer = CALayer()
            let borderFrame = CGRect(x: -4, y: -4, width: channelImage.frame.size.width+8, height: channelImage.frame.size.width+8)
            borderLayer.frame = borderFrame
            borderLayer.cornerRadius = 4
            borderLayer.borderWidth = 0.5
            borderLayer.borderColor = UIColor.lightGray.cgColor
            channelImage.layer.insertSublayer(borderLayer, at: 0)
            channelImage.layer.masksToBounds = false
            borderLayer.backgroundColor = UIColor.lightGray.cgColor
            self.channelImage.layoutIfNeeded()
            self.channelImage.layoutSubviews()
        }
    }

没有背景色:

@IBOutlet weak var channelImage: UIImageView! {
    didSet {
        let borderLayer = CALayer()
        let borderFrame = CGRect(x: -4, y: -4, width: channelImage.frame.size.width+8, height: channelImage.frame.size.width+8)
        borderLayer.frame = borderFrame
        borderLayer.cornerRadius = 4
        borderLayer.borderWidth = 0.5
        borderLayer.borderColor = UIColor.lightGray.cgColor
        channelImage.layer.insertSublayer(borderLayer, at: 0)
        channelImage.layer.masksToBounds = false
        self.channelImage.layoutIfNeeded()
        self.channelImage.layoutSubviews()
    }
}

这里还有引用第一个和第二个例子的图片:

我做了很多搜索，但没有找到适合我的情况的答案。

这里是这个Cell的完整代码

class ChannelCell: UITableViewCell, ChannelSettable {

    static let reusableID = "channelCell"

    var channel: Channel? = nil {
        didSet {
            self.channelName.text = channel?.channelName ?? ""
            self.channelImage.image = UIImage(named: channel?.channel ?? "") ?? UIImage(named: "TV")
            self.channelCategory.text = channel?.chCategory ?? ""
        }
    }

    @IBOutlet weak var channelName: UILabel!
    @IBOutlet weak var channelCategory: UILabel!
    @IBOutlet weak var channelImage: UIImageView! {
        didSet {
            let borderLayer = CALayer()
            let borderFrame = CGRect(x: -4, y: -4, width: channelImage.frame.size.width+8, height: channelImage.frame.size.width+8)
            borderLayer.frame = borderFrame
            borderLayer.cornerRadius = 4
            borderLayer.borderWidth = 0.5
            borderLayer.borderColor = UIColor.lightGray.cgColor
            borderLayer.backgroundColor = UIColor.lightGray.cgColor
            channelImage.layer.insertSublayer(borderLayer, at: 0)
            channelImage.layer.masksToBounds = false
        }
    }

    override func awakeFromNib() {
        super.awakeFromNib()
        self.channelName.font = DesignHelper.channelNameFont
        self.channelCategory.font = DesignHelper.channelCategoryFont
        self.layoutIfNeeded()
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)
    }
}

Answer 1

您可以像这样直接向 UIImageView 的图层添加边框:

channelImage.layer.borderWidth = 0.5
channelImage.layer.borderColor = UIColor.lightGray.cgColor

您不必费心使用额外的层来做到这一点。

但是，如果您仍然需要添加一个额外的 CALayer，请尝试使用这些方法:

func insertSublayer(CALayer, above: CALayer?)
func insertSublayer(CALayer, below: CALayer?)