使用UIImageView在UIView中剪切透明孔

Question

因此，我正在尝试为我的QR摄像机视图创建以下图像。

我有一个用于摄像机覆盖的图像（它是屏幕中间的正方形）。

我查看了关于stackoverflow的类似主题，并了解了如何从黑色背景（0.75％透明）中切出相机覆盖图像，使其在中间留有空白，但是在放置时确实存在一些实际问题，而且我无法找出奇怪的地方。

这里是我用来创建背景黑色图像并在中心切出正方形的代码：

        // Create a view filling the screen.
    let backgroundView = UIView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height))

    // Set a semi-transparent, black background.
    backgroundView.backgroundColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.75)

    // Create the initial layer from the view bounds.
    let maskLayer = CAShapeLayer()
    maskLayer.frame = backgroundView.bounds
    maskLayer.fillColor = UIColor.black.cgColor

    // Create the path.
    let path = UIBezierPath(rect: backgroundView.bounds)
    maskLayer.fillRule = CAShapeLayerFillRule.evenOdd

    // Append the overlay image to the path so that it is subtracted.
    path.append(UIBezierPath(rect: camOverlayImageView.frame))
    maskLayer.path = path.cgPath

    // Set the mask of the view.
    backgroundView.layer.mask = maskLayer

    // Add the view so it is visible.
    self.view.addSubview(backgroundView)

camOverlayImageView是在情节提要中创建的，并且所有在其上使用的im都是将其垂直和水平居中放置在Superview上的约束，如下所示：

但是，当我这样做时，这就是我在设备上得到的：

[如果有人可能知道这是什么原因或如何解决，将不胜感激，因为我似乎找不到它。

我当然可以手动移动框架并像这样偏移它，但这不是正确的方法：

        let overlayFrame = camOverlayImageView.frame
    // Append the overlay image to the path so that it is subtracted.
    path.append(UIBezierPath(rect: CGRect(
        x: overlayFrame.origin.x + 18,
        y: overlayFrame.origin.y - 6,
        width: overlayFrame.size.width,
        height: overlayFrame.size.height))
    )
    maskLayer.path = path.cgPath

而不是做我以前的工作：

    path.append(UIBezierPath(rect: camOverlayImageView.frame))
maskLayer.path = path.cgPath

Answer 1

最有可能...

您创建蒙版还为时过早-在自动布局确定视图大小/放置视图之前。

尝试这样：

class HoleInViewController: UIViewController {

    @IBOutlet var camOverlayImageView: UIView!

    let backgroundView: UIView = {
        let v = UIView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = UIColor.black.withAlphaComponent(0.75)
        return v
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(backgroundView)
        NSLayoutConstraint.activate([
            backgroundView.topAnchor.constraint(equalTo: view.topAnchor),
            backgroundView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            backgroundView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            backgroundView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])

    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        // Create the initial layer from the view bounds.
        let maskLayer = CAShapeLayer()
        maskLayer.frame = backgroundView.bounds
        maskLayer.fillColor = UIColor.black.cgColor

        // Create the path.
        let path = UIBezierPath(rect: backgroundView.bounds)
        maskLayer.fillRule = CAShapeLayerFillRule.evenOdd

        // Append the overlay image to the path so that it is subtracted.
        path.append(UIBezierPath(rect: camOverlayImageView.frame))
        maskLayer.path = path.cgPath

        // Set the mask of the view.
        backgroundView.layer.mask = maskLayer

    }

}