iOS 8 Swift - 写入 PDF 时出现上下颠倒的文本

Question

我正在处理一个项目，该项目将采用现有的 PDF 模板，并且能够将文本写入文本（当前存储为用户默认值）到该模板，然后在 UIWebView 中显示带有注释的更新 PDF。

我已经为此创建了一个函数，并且到目前为止能够在我想要的位置显示带有注释的 PDF，但是文本出现颠倒（PDF 模板是正确的方向）。我知道在使用核心图形和绘制 PDF 时，上下文的 (0,0) 位置位于左下角，与左上角相对。然而，即使在尝试翻转 y 轴之后，我仍然在努力让文本正确显示。

else {
            //Set up the webView to show the pdf file

            //Create NSURL for the pdf document
            var localUrl: NSURL = NSBundle.mainBundle().URLForResource("Original PDF", withExtension: "pdf")!

            //references the PDF's location
            var pdfDocumentRef: CGPDFDocumentRef = CGPDFDocumentCreateWithURL(localUrl as CFURLRef)

            //establishing the height and width of the PDF file
            var paperSize = CGRectMake(0.0, 0.0, 595.276, 841.89)

            //create a tempory filename for this PDF and temporary path
            var path = NSTemporaryDirectory()
            var temporaryPdfFilePath = path.stringByAppendingPathComponent("temporaryPDF.pdf")

            //creation of a new graphical context, if no file is present at specified path, then a new path is created.
            var graphicsContext = UIGraphicsBeginPDFContextToFile(temporaryPdfFilePath, paperSize, nil)

            //starts a new PDF page that can have graphical context drawn, parameters specify size and location of new PDF, and any additional page information (currently nil)
            UIGraphicsBeginPDFPageWithInfo(paperSize, nil)

            //gets the current context
            var currentContext: CGContextRef = UIGraphicsGetCurrentContext()

            //access page 1 of the PDF
            var page: CGPDFPageRef = CGPDFDocumentGetPage(pdfDocumentRef, 1)

            //changes the origin of the coordinate system. parameters of current context, x coordinate (displaces by 0), y coordinate (displaces by paperSize height)
            CGContextTranslateCTM(currentContext, 0, paperSize.height)

            //changes the scale of the user coordinate system. parameters of current context, x axis (doesn't change factor), y axis (changes scale by -1 (to flip vertically))
            CGContextScaleCTM(currentContext, 1.0, -1.0)

            //draw to page 1 of the graphics context
            CGContextDrawPDFPage(currentContext, page)

            //Add some text to be displayed
            let font = UIFont(name: "Courier", size: 14)
            let text: String = userDefaults.stringForKey("name")!
            let rectText = CGRectMake(25, 345, 100, 100)
            let textStyle = NSMutableParagraphStyle.defaultParagraphStyle().mutableCopy() as NSMutableParagraphStyle
            let textColor = UIColor.blackColor()
            let textFontAttributes = [
                NSFontAttributeName : font!,
                NSForegroundColorAttributeName: textColor,
                NSParagraphStyleAttributeName: textStyle
            ]

            text.drawInRect(rectText, withAttributes: textFontAttributes)


            //closes the PDF Graphics context
            UIGraphicsEndPDFContext()

            //show in webView
            let testUrl:NSURL = NSURL(string: temporaryPdfFilePath)!
            let testUrlRequest: NSURLRequest = NSURLRequest(URL: testUrl)
            self.webView.loadRequest(testUrlRequest)

        }

我有一种感觉，我只是缺少与图形上下文设置方式有关的一些小东西。如果有人能指出我正确的方向，我将不胜感激？

谢谢

Answer 1

在 Swift 3 中

    currentContext?.textMatrix = .identity
    currentContext?.translateBy(x: 0, y: 100)
    currentContext?.scaleBy(x: 1, y: -1)

Answer 2

您还需要转换文本空间。所以试试这个翻转坐标系：

CGContextSetTextMatrix(currentContext, CGAffineTransformIdentity)
CGContextTranslateCTM(currentContext, 0, paperSize.height)
CGContextScaleCTM(currentContext, 1, -1)