Swift 4和UIPrintPageRenderer不打印文本

Question

当WKWebView完成加载时，我正在将Swift 4与WKWebView一起使用，我想获取Webview并生成PDF，一切正常，除了我打印时，文本未从WKWebView出现，所有边框和td单元格都没有颜色会显示，但文本不会显示。

这是我的代码：

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {

        self.stopIndicator()

        //Assign the Web View as the View

        view = webView

        var newheight = CGFloat()
        var newwidth = CGFloat()

        self.webView.evaluateJavaScript("document.readyState", completionHandler: { (complete, error) in

            if complete != nil {

                self.webView.evaluateJavaScript("document.body.scrollHeight", completionHandler: { (height, error) in

                    newheight = height as! CGFloat

                    self.webView.evaluateJavaScript("document.body.scrollWidth", completionHandler: { (width, error) in

                        newwidth = width as! CGFloat

                        //Define the render, an object that draws pages of content that are to be printed, with or without the assistance of print formatters.

                        let render = UIPrintPageRenderer()

                        //Assign the Web View to the print page renderer

                        render.addPrintFormatter(webView.viewPrintFormatter(), startingAtPageAt: 0)

                        //Define the page size of the PDF Document

                        let page = CGRect(x: 0, y: 0, width: newwidth, height: newheight)

                        //Define the print page size

                        let printable = page.insetBy(dx: 0, dy: 0)

                        //Set the size for the render page

                        render.setValue(NSValue(cgRect: page), forKey: "paperRect")

                        //Set the size for the render printable

                        render.setValue(NSValue(cgRect: printable), forKey: "printableRect")

                        let rect = CGRect(x: 0, y: 0, width: newwidth, height: newheight)

                        //Define the PDF Data variable

                        let pdfData = NSMutableData()

                        //Creates a PDF-based graphics context that targets the specified mutable data object.

                        UIGraphicsBeginPDFContextToData(pdfData, rect, nil)

                        //For each pages in the render

                        for i in 0...render.numberOfPages {

                            //Marks the beginning of a new page in a PDF context and configures it using default values.

                            UIGraphicsBeginPDFPage();

                            //Define the current page bounds.

                            let bounds = UIGraphicsGetPDFContextBounds()

                            //Draw the page on content

                            render.drawPage(at: i, in: bounds)

                        }

                        //Closes a PDF graphics context and pops it from the current context stack.

                        UIGraphicsEndPDFContext();

                        //Get the first directory path.

                        let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]

                        //Write the PDF Data to the file.

                        pdfData.write(toFile: "\(documentsPath)/pdfName.pdf", atomically: true)

                        //Set the PDF file path

                        self.pdfPath = "\(documentsPath)/pdfName.pdf"

                        //Set the PDF title

                        self.pdfTitle = "pdfName"

                        self.shareButton.isEnabled = true



                    })
                })
            }

        })

    }

完成Web视图的加载后，上面的此方法将从Web视图生成PDF，但是问题是没有文本生成。我在做什么错了？