我有一个“屏幕外”的 UIView 层次结构，我想在屏幕的不同位置呈现它。此外，应该可以仅显示此 View 层次结构的一部分，并应反射(reflect)对该层次结构所做的所有更改。

难点:

• UIView 方法 drawHierarchy(in:afterScreenUpdates:) 总是调用 draw(_ rect:)，因此对于大型层次结构来说效率非常低如果您想将所有更改合并到 View 层次结构中。您必须在每次屏幕更新时重新绘制它或观察所有 View 的所有更改属性。 Draw view hierarchy documentation
• UIView 方法 snapshotView(afterScreenUpdates:) 也没有多大帮助，因为如果此层次结构“关闭”，我还没有找到获得正确 View 层次结构图的方法-屏幕”。 Snapshot view documentation

“Off-Screen”:此 View 层次结构的 Root View 不是应用程序 UI 的一部分。它没有 super View 。

您可以在下面看到我的想法的直观表示:

最佳答案

下面是我将如何着手去做。首先，我会复制您要复制的 View 。我为此写了一个小扩展:

extension UIView {
    func duplicate<T: UIView>() -> T {
        return NSKeyedUnarchiver.unarchiveObject(with: NSKeyedArchiver.archivedData(withRootObject: self)) as! T
    }

    func copyProperties(fromView: UIView, recursive: Bool = true) {
        contentMode = fromView.contentMode
        tag = fromView.tag

        backgroundColor = fromView.backgroundColor
        tintColor = fromView.tintColor

        layer.cornerRadius = fromView.layer.cornerRadius
        layer.maskedCorners = fromView.layer.maskedCorners

        layer.borderColor = fromView.layer.borderColor
        layer.borderWidth = fromView.layer.borderWidth

        layer.shadowOpacity = fromView.layer.shadowOpacity
        layer.shadowRadius = fromView.layer.shadowRadius
        layer.shadowPath = fromView.layer.shadowPath
        layer.shadowColor = fromView.layer.shadowColor
        layer.shadowOffset = fromView.layer.shadowOffset

        clipsToBounds = fromView.clipsToBounds
        layer.masksToBounds = fromView.layer.masksToBounds
        mask = fromView.mask
        layer.mask = fromView.layer.mask

        alpha = fromView.alpha
        isHidden = fromView.isHidden
        if let gradientLayer = layer as? CAGradientLayer, let fromGradientLayer = fromView.layer as? CAGradientLayer {
            gradientLayer.colors = fromGradientLayer.colors
            gradientLayer.startPoint = fromGradientLayer.startPoint
            gradientLayer.endPoint = fromGradientLayer.endPoint
            gradientLayer.locations = fromGradientLayer.locations
            gradientLayer.type = fromGradientLayer.type
        }

        if let imgView = self as? UIImageView, let fromImgView = fromView as? UIImageView {
            imgView.tintColor = .clear
            imgView.image = fromImgView.image?.withRenderingMode(fromImgView.image?.renderingMode ?? .automatic)
            imgView.tintColor = fromImgView.tintColor
        }

        if let btn = self as? UIButton, let fromBtn = fromView as? UIButton {
            btn.setImage(fromBtn.image(for: fromBtn.state), for: fromBtn.state)
        }

        if let textField = self as? UITextField, let fromTextField = fromView as? UITextField {
            if let leftView = fromTextField.leftView {
                textField.leftView = leftView.duplicate()
                textField.leftView?.copyProperties(fromView: leftView)
            }

            if let rightView = fromTextField.rightView {
                textField.rightView = rightView.duplicate()
                textField.rightView?.copyProperties(fromView: rightView)
            }

            textField.attributedText = fromTextField.attributedText
            textField.attributedPlaceholder = fromTextField.attributedPlaceholder
        }

        if let lbl = self as? UILabel, let fromLbl = fromView as? UILabel {
            lbl.attributedText = fromLbl.attributedText
            lbl.textAlignment = fromLbl.textAlignment
            lbl.font = fromLbl.font
            lbl.bounds = fromLbl.bounds
        }

       if recursive {
            for (i, view) in subviews.enumerated() {
                if i >= fromView.subviews.count {
                    break
                }

                view.copyProperties(fromView: fromView.subviews[i])
            }
        }
    }
}

要使用这个扩展，只需做

let duplicateView = originalView.duplicate()
duplicateView.copyProperties(fromView: originalView)
parentView.addSubview(duplicateView)

然后我将屏蔽重复 View 以仅获取您想要的特定部分

let mask = UIView(frame: CGRect(x: 0, y: 0, width: yourNewWidth, height: yourNewHeight))
mask.backgroundColor = .black
duplicateView.mask = mask

最后，我会使用 CGAffineTransform 将其缩放到您想要的任何大小

duplicateView.transform = CGAffineTransform(scaleX: xScale, y: yScale)

copyProperties 函数应该运行良好，但您可以根据需要更改它以将更多内容从一个 View 复制到另一个 View 。

祝你好运，让我知道进展如何:)

关于ios - 高效的离屏UIView渲染和镜像，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54276729/