介绍
对 UIScrollView 及其子类 UITableView、UICollectionView 的内容进行长截图。
思路
对 UIScrollView进行长截屏时，需要知道它的全部内容，包括未加载未渲染的内容。
做法是通过设置它的内容偏移量 contentOffset， 让 ScrollView 的内容滑动到底部，这样便可以触发 ScrollView 中全部内容的加载和渲染。
用 CoreGraphics 对 ScrollView 的内容渲染生成图片，此时我们需要令 ScrollView 的宽高等于 它 contentSize 的真实宽高，在截屏结束后再恢复，因此需要提前缓存一份 ScrollView 的属性。
问题
Q：设置 ScrollView 偏移量时，用户看见的界面内容会发生偏移，怎么处理？
A：在设置偏移之前，使用 UIView 的 func snapshotView(afterScreenUpdates afterUpdates: Bool) -> UIView? 方法对当前看见的内容截屏（注意：此方法只会截屏已显示加载出来的内容，非全部），然后用 addSubview() 添加 Scrollview.superView上，盖在 UIScrollView 之上，这样用户看见的就是一个假的不会变动的View。
使用：
scrollView.swContentCapture { (image) in
// TODO:
}
全部代码如下：
代码中有详细注释
// Reference: https://github.com/startry/SwViewCapture
// Notes: The 'swContentCapture(_:)' method would lose constraints of UIScrollview, we need remake its constraints after screenshot.
import UIKit
public extension UIScrollView {
func swContentCapture (_ completionHandler: @escaping (_ capturedImage: UIImage?) -> Void) {
// Put a fake Cover of View
let snapShotView = self.snapshotView(afterScreenUpdates: false)
snapShotView?.frame = CGRect(x: self.frame.origin.x, y: self.frame.origin.y, width: (snapShotView?.frame.size.width)!, height: (snapShotView?.frame.size.height)!)
self.superview?.addSubview(snapShotView!)
// Backup all properties of scrollview if needed
let bakFrame = self.frame
let bakOffset = self.contentOffset
let bakSuperView = self.superview
let bakIndex = self.superview?.subviews.firstIndex(of: self)
// Scroll To Bottom show all cached view
if self.frame.size.height < self.contentSize.height {
self.contentOffset = CGPoint(x: 0, y: self.contentSize.height - self.frame.size.height)
}
self.swRenderImageView({ [weak self] (capturedImage) -> Void in
// Recover View
let strongSelf = self!
strongSelf.removeFromSuperview()
strongSelf.frame = bakFrame
strongSelf.contentOffset = bakOffset
bakSuperView?.insertSubview(strongSelf, at: bakIndex!)
snapShotView?.removeFromSuperview()
completionHandler(capturedImage)
})
}
private func swRenderImageView(_ completionHandler: @escaping (_ capturedImage: UIImage?) -> Void) {
// Due to scroll to bottom, delay to wait for contentOffset refreshing.
DispatchQueue.main.asyncAfter(deadline: .now() + 0.6) {
// Rebuild scrollView superView and their hold relationship
let swTempRenderView = UIView(frame: CGRect(x: 0, y: 0, width: self.contentSize.width, height: self.contentSize.height))
self.removeFromSuperview()
swTempRenderView.addSubview(self)
self.contentOffset = CGPoint.zero
self.frame = swTempRenderView.bounds
// Sometimes ScrollView will Capture nothing without defer;
DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
let bounds = self.bounds
UIGraphicsBeginImageContextWithOptions(bounds.size, false, UIScreen.main.scale)
self.layer.render(in: UIGraphicsGetCurrentContext()!)
let capturedImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
completionHandler(capturedImage)
}
}
}
}
