“监听用户截屏”弹出分享窗口

从 iOS 7 开始，苹果提供了监听用户截屏操作的通知：

@available(iOS 7.0, *)
public static let UIApplicationUserDidTakeScreenshot: NSNotification.Name

我们可以使用这个通知来做例如：截屏弹出分享窗口的功能。

// 监听通知
NotificationCenter.default.addObserver(self, selector: #selector(screenShot), name: Notification.Name.UIApplicationUserDidTakeScreenshot, object: nil)

func screenShot() {
        let image = fullScreenShot(tableView)

        let activityVC = UIActivityViewController(activityItems: [image], applicationActivities:  nil)

        self.present(activityVC, animated: true, completion: nil)
 }

// 有时，需要截取 tableView 或 scrollView 的全部内容，使用以下方法：
/// 长截屏
func fullScreenShot(_ scrollView: UIScrollView) -> UIImage {
        // 记录当前 scrollView 的"偏移量"和"坐标"
        let savedContentOffset = scrollView.contentOffset
        let savedScrollViewFrame = scrollView.frame
        
        scrollView.contentOffset = .zero
        scrollView.frame = CGRect(origin: .zero, size: scrollView.contentSize)
        
        UIGraphicsBeginImageContextWithOptions(scrollView.contentSize, true, UIScreen.main.scale)
        scrollView.layer.render(in: UIGraphicsGetCurrentContext()!)
        let image = UIGraphicsGetImageFromCurrentImageContext()!
        
        // 重置
        scrollView.contentOffset = savedContentOffset
        scrollView.frame = savedScrollViewFrame
        
        UIGraphicsEndImageContext()
        
        return image
}