如何截取 UIView 的一部分？

Question

我希望用户在 Swift 中以编程方式按下按钮后继续我的应用程序并截取该应用程序的屏幕截图。我知道 UIGraphicsGetImageFromCurrentImageContext() 会截取屏幕截图，但我不想要整个屏幕的图片。我想要弹出一个矩形（有点像裁剪工具），用户可以拖动矩形并调整其大小以仅截取屏幕的特定部分。我希望矩形覆盖 WKWebView 并裁剪网络视图的图片。

Answer 1

这是之前在 How to capture UIView to UIImage without loss of quality on retina display 提出的问题，但要在 swift (2.3) 中展开：

extension UIView {

    class func image(view: UIView) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.opaque, 0.0)
        guard let ctx = UIGraphicsGetCurrentContext() else {
            return nil
        }
        view.layer.renderInContext(ctx)
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return img
    }

    func image() -> UIImage? {
        return UIView.image(self)
    }
}

因此您可以使用 UIView.image(theView) 从视图中获取图像，或者通过询问视图本身 let viewImage = self.view.image()

请记住，尽管这很粗糙，可能需要进一步研究线程安全等问题....

Answer 2

标准快照技术是drawHierarchy(in:afterScreenUpdates:), drawing that to an image context. In iOS 10 and later, you can use UIGraphicsImageRenderer:

extension UIView {

    /// Create image snapshot of view.
    ///
    /// - Parameters:
    ///   - rect: The coordinates (in the view's own coordinate space) to be captured. If omitted, the entire `bounds` will be captured.
    ///   - afterScreenUpdates: A Boolean value that indicates whether the snapshot should be rendered after recent changes have been incorporated. Specify the value false if you want to render a snapshot in the view hierarchy’s current state, which might not include recent changes. Defaults to `true`.
    ///
    /// - Returns: The `UIImage` snapshot.

    func snapshot(of rect: CGRect? = nil, afterScreenUpdates: Bool = true) -> UIImage {
        return UIGraphicsImageRenderer(bounds: rect ?? bounds).image { _ in
            drawHierarchy(in: bounds, afterScreenUpdates: afterScreenUpdates)
        }
    }
}

你会像这样使用它：

let image = webView.snapshot(of: rect)

在iOS10之前，你会得到一个图像的一部分，你可以使用CGImage方法cropping(to:)。例如：

extension UIView {

    /// Create snapshot
    ///
    /// - Parameters:
    ///   - rect: The coordinates (in the view's own coordinate space) to be captured. If omitted, the entire `bounds` will be captured.
    ///   - afterScreenUpdates: A Boolean value that indicates whether the snapshot should be rendered after recent changes have been incorporated. Specify the value false if you want to render a snapshot in the view hierarchy’s current state, which might not include recent changes. Defaults to `true`.
    ///
    /// - Returns: Returns `UIImage` of the specified portion of the view.

    func snapshot(of rect: CGRect? = nil, afterScreenUpdates: Bool = true) -> UIImage? {
        // snapshot entire view

        UIGraphicsBeginImageContextWithOptions(bounds.size, isOpaque, 0)
        drawHierarchy(in: bounds, afterScreenUpdates: afterScreenUpdates)
        let wholeImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        // if no `rect` provided, return image of whole view

        guard let image = wholeImage, let rect = rect else { return wholeImage }

        // otherwise, grab specified `rect` of image

        guard let cgImage = image.cgImage?.cropping(to: rect * image.scale) else { return nil }
        return UIImage(cgImage: cgImage, scale: image.scale, orientation: .up)
    }

}

其中使用了这个方便的小运算符：

extension CGRect {
    static func * (lhs: CGRect, rhs: CGFloat) -> CGRect {
        return CGRect(x: lhs.minX * rhs, y: lhs.minY * rhs, width: lhs.width * rhs, height: lhs.height * rhs)
    }
}

要使用它，您可以这样做：

if let image = webView.snapshot(of: rect) {
    // do something with `image` here
}

对于 Swift 2 版本，请参阅 previous revision of this answer。

如何截取 UIView 的一部分？

How to take screenshot of portion of UIView?

screenshot

ios

swift

wkwebview