背景

  某日产品拿来了一个由30多页高清长图生成的pdf，在应用中运行出现了崩溃。

排查

  经过调试发现加载长图生成的pdf时，运行内存会出现缓慢增长，直至崩溃。经过代码定位发现时pdf转成image对象的过程中由于是长图生成的pdf，这一页的pdf的size相当于正常pdfsize的30多页，转换的过程中context的fill的size也是正常pdf的30多倍。经过调研，尝试，发现对于同一页的pdf，可以通过调整context的fill的size来只把pdf中的部分内容转换成image对象，内存正常也不大。

方案

  原来的方案是每页pdf生成一个image对象，通过一个collectonViewCell来显示。调整后的方案为：根据屏幕大小来决定一个pdf页面生成多少个image对象，有多少个image对象，一个section里就有多少个cell。方案如下：

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {if pdfSize.height/pdfSize.width >= 3.0 { //长图生成的pdf 备注：pdfSize 即一页pdf的大小let visible_width = pdfSize.widthlet visible_height = visible_width * Board_height/Board_widthlet visibleSize = CGSize(width: visible_width, height: visible_height)let count:Int = Int(ceil(pdfSize.height/visible_height))// 计算需要分割的次数let index:Intlet itemSize:CGSizeif indexPath.item < count {index = indexPath.item} else {index = count - 1}if CGFloat(index) * visibleSize.height + visibleSize.height < pdfSize.height {itemSize = visibleSize} else {let tailHeight = pdfSize.height - CGFloat(index) * visibleSize.heightitemSize = CGSize(width: visibleSize.width, height: tailHeight)}return itemSize}return pdfSize}

在讲pdf转成image对象的过程中，方案调整核心代码如下：

//index就是pdf中的从上往下被分割后的image的索引值private func subImageFromLongPDF(ori_page:PDFPage, pdfSize:CGSize, index:Int) -> UIImage {guard let page = ori_page.pageRef else {return UIImage()}var dic = [PDFAnnotation:CGRect]()let originalPageRect = ori_page.originalPageRectlet elaborate: CGFloat = 1.0let scale_W = pdfSize.width / originalPageRect.size.width * elaboratelet scale_H = pdfSize.height / originalPageRect.size.height * elaboratelet width = originalPageRect.size.width * scale_Wlet height = width * Board_height/Board_width // Board_height屏幕高度，Board_width屏幕宽度let visibleSize = CGSize(width: width, height: height)let rotation = ori_page.rotationori_page.rotation = 0let scaledOrigin = CGPoint(x: originalPageRect.origin.x * scale_W, y: originalPageRect.origin.y * scale_H)let scaledPageSize = CGSize(width: originalPageRect.size.width * scale_W, height: originalPageRect.size.height * scale_H)let scaledPageRect:CGRectvar tailHeight = 0.0if CGFloat(index) * visibleSize.height + height < scaledPageSize.height {scaledPageRect = CGRect(origin: CGPoint(x: 0, y: CGFloat(index) * visibleSize.height), size: visibleSize)} else {tailHeight = scaledPageSize.height - CGFloat(index) * visibleSize.heightscaledPageRect = CGRect(origin: CGPoint(x: 0, y: CGFloat(index) * visibleSize.height), size: CGSize(width: visibleSize.width, height: tailHeight))}var img:UIImage?autoreleasepool {let renderer = UIGraphicsImageRenderer(size: scaledPageRect.size)var tmpImg:UIImage? = renderer.image {ctx inUIColor.white.set()//这个核心代码，scaledPageRect就是计算好的rect，ctx.fill(scaledPageRect)let rotationAngle: CGFloatswitch page.rotationAngle {//保持和安卓一致，强制为0了case 90:rotationAngle = 270//平移 以用户空间为单位，指定上下文的坐标空间 x 轴的位移量。ctx.cgContext.translateBy(x: -scaledPageRect.origin.x, y: 0)case 180:rotationAngle = 180//平移ctx.cgContext.translateBy(x: scaledPageRect.width,y: 0)case 270:rotationAngle = 90//平移ctx.cgContext.translateBy(x: scaledPageRect.origin.x, y: scaledPageRect.size.height - scaledPageRect.origin.y)default:rotationAngle = 0//平移 以用户空间为单位，指定上下文的坐标空间 x 轴的位移量。//指定上下文的坐标空间 y 轴的位移量（以用户空间为单位）。if rotation == 180 {if tailHeight > 0 {//尾部不足一屏的特殊处理逻辑ctx.cgContext.translateBy(x: 0 - scaledOrigin.x, y: 0 + scaledOrigin.y + CGFloat(index+1) * visibleSize.height - (visibleSize.height - tailHeight))//翻转180度正常} else {ctx.cgContext.translateBy(x: 0 - scaledOrigin.x, y: 0 + scaledOrigin.y + CGFloat(index+1) * visibleSize.height)//翻转180度正常}} else {ctx.cgContext.translateBy(x: 0 - scaledOrigin.x, y: scaledPageSize.height + scaledOrigin.y - scaledPageRect.origin.y)}}//Rotate是以原点为圆心旋转,Quartz创建的图形上下文旋转圆心为左下角，角度值正数为逆时针旋转，负数为顺时针旋转//UIKit创建的图像上下文旋转圆心为左上角,角度值正数为顺时针旋转，负数为逆时针旋转。// Flip the context vertically because the Core Graphics coordinate system starts from the bottom.ctx.cgContext.scaleBy(x:1.0, y: -1.0)//垂直翻转上下文，因为核心图形坐标系从底部开始//旋转 正值逆时针旋转，负值顺时针旋转ctx.cgContext.rotate(by: rotationAngle.degreesToRadians)ctx.cgContext.scaleBy(x: scale_W, y: scale_H)//缩放// Draw the PDF page.// 此处仍然是正常的绘制pdf，因为前面设置了context的fillSize，因此pdf绘制的时候只在前面指定的rect才会生效。ctx.cgContext.drawPDFPage(page)for annotation in ori_page.annotations {let origin = annotation.bounds.origindic[annotation] = annotation.boundslet annotation_fill_bounds = CGRect(x: origin.x + originalPageRect.origin.x, y: origin.y + originalPageRect.origin.y, width: annotation.bounds.size.width, height: annotation.bounds.size.height)annotation.bounds = annotation_fill_boundsannotation.draw(with: .cropBox, in: ctx.cgContext)}}if rotation%360 != 0 {let scale:Float =  Float(rotation) / Float(180)tmpImg = tmpImg?.rotate(radians: Float.pi * scale) ?? UIImage.init()}img = tmpImgtmpImg = nil}//将对pdfpage的修改进行还原ori_page.rotation = rotationfor (annotation,bounds) in dic {annotation.bounds = bounds}return img ?? UIImage()}extension PDFPage {var originalPageRect: CGRect {switch rotation {case 90, 270:let originalRect = bounds(for: PDFDisplayBox.cropBox)let rotatedSize = CGSize(width: originalRect.height, height: originalRect.width)return CGRect(origin: originalRect.origin, size: rotatedSize)default:return bounds(for: PDFDisplayBox.cropBox)}}
}extension UIImage {func rotate(radians: Float) -> UIImage? {var newSize = CGRect(origin: CGPoint.zero, size: self.size).applying(CGAffineTransform(rotationAngle: CGFloat(radians))).size// Trim off the extremely small float value to prevent core graphics from rounding it upnewSize.width = floor(newSize.width)newSize.height = floor(newSize.height)UIGraphicsBeginImageContextWithOptions(newSize, false, self.scale)guard let context = UIGraphicsGetCurrentContext() else {return nil}// Move origin to middlecontext.translateBy(x: newSize.width/2, y: newSize.height/2)// Rotate around middlecontext.rotate(by: CGFloat(radians))// Draw the image at its centerself.draw(in: CGRect(x: -self.size.width/2, y: -self.size.height/2, width: self.size.width, height: self.size.height))let newImage = UIGraphicsGetImageFromCurrentImageContext()UIGraphicsEndImageContext()return newImage}
}extension FloatingPoint {var degreesToRadians: Self { return self * .pi / 180 }var radiansToDegrees: Self { return self * 180 / .pi }
}

备注：这段代码结合了自己的项目实际业务，大家作为参考。多看下核心代码和注释