ios - 将图像添加到 CAShapeLayer

Question

我正在尝试在嵌套在 UIView 层中的 CAShapeLayer 内渲染静态图像。形状的所有装饰(即边框、颜色、路径等)都会在 View 中正确渲染。

但是，为CALayer.contents属性提供的CGImage在任何时候都不会在 View 中呈现(据我所知告诉)。我已经尝试弄清楚这种行为有一段时间了，但对 Apple 的文档感到困惑:

If you are using the layer to display a static image, you can set this property to the CGImage containing the image you want to display.... Assigning a value to this property causes the layer to use your image rather than create a separate backing store.

If the layer object is tied to a view object, you should avoid setting the contents of this property directly. The interplay between views and layers usually results in the view replacing the contents of this property during a subsequent update.

很高兴知道!这可能正是这种情况下发生的情况:UIView 正在更新并替换其内容。除了提供的解决方法不是很清楚，而且我无法找到解决此问题的示例。

有人对如何在 CAShapeLayer 上“间接”设置静态图像并避免其被 super View 删除(几乎立即)有任何建议吗？

Answer 1

起初我以为你无法将图像安装到 CAShapeLayer 的内容中并使其工作，但我错了。它确实有效。考虑这段代码:

class ImageWithShapeView: UIView {

    let shapeLayer = CAShapeLayer()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        layer.borderWidth = 1.0
        shapeLayer.frame = self.bounds
        //Load an image into the shape layer's contents property.
        if let image = UIImage(named: "WareToLogo") {
            shapeLayer.contents = image.cgImage
            layer.addSublayer(shapeLayer)
        }
        let path = UIBezierPath()
        shapeLayer.lineWidth = 2.0
        shapeLayer.strokeColor = UIColor.blue.cgColor
        shapeLayer.fillColor = UIColor.clear.cgColor
        let radius = (bounds.midX + bounds.midY) / 4.0
        path.addArc(withCenter: CGPoint(x: bounds.midX, y: bounds.midY), radius: radius, startAngle: 0, endAngle: CGFloat.pi * 2, clockwise: true)
        path.move(to: CGPoint(x:0, y:0))
        path.addLine(to: CGPoint(x: bounds.width, y: bounds.height))
        path.move(to: CGPoint(x: bounds.width, y: 0))
        path.addLine(to: CGPoint(x: 0, y: bounds.height))
        shapeLayer.path = path.cgPath
    }
}

这有效，并在我添加 ImageWithShapeView 时创建以下内容到我的项目。 (我使用的是 Storyboard，所以我实现了 UIView.init(coder:) 。如果您在代码中创建 View ，您可能需要实现 UIView.init(frame:) )