Swift iOS - 使用 PDFKit 和 UI 将文本覆盖到 PDF 上

Question

我正在 Swift 5 和 iOS 上工作。我正在尝试将文本覆盖到我当前拥有的 PDF 上。我本质上是在移植从 macOS 应用程序编写的代码。这是Mac版本的代码：

func executeContext(at srcURL: URL, to dstURL: URL) {
    
    // Confirm there is a document there
    if let doc: PDFDocument = PDFDocument(url: srcURL) {
        
        // Create a document, get the first page, and set the size of the page
        let page: PDFPage = doc.page(at: 0)!
        var mediaBox: CGRect = CGRect(x: 0, y: 0, width: 792, height: 612)
        
        // This is where the magic happens.  Create the drawing context on the PDF
        let context = CGContext(dstURL as CFURL, mediaBox: &mediaBox, nil)
        let graphicsContext = NSGraphicsContext(cgContext: context!, flipped: false)
        NSGraphicsContext.current = graphicsContext
        
        context!.beginPDFPage(nil)
        
        // Draws the PDF into the context
        page.draw(with: .mediaBox, to: context!)
        
        // Parse and Draw Text on the context
        //drawText()
        
        let attributes = [
            NSAttributedString.Key.font: UIFont.boldSystemFont(ofSize: 72)
        ]
        let text = "I'm a PDF!"
        text.draw(at: CGPoint(x: 0, y: 0), withAttributes: attributes)
        
        context!.saveGState()
        
        context!.restoreGState()
        
        context!.endPDFPage()
        NSGraphicsContext.current = nil
        context?.closePDF()
    }
}

该drawText()函数完成了大部分所需的文本覆盖，但我在其下方放置了另一个“绘制”方法来测试它。

我收到错误是可以理解的，Cannot find 'NSGraphicsContext' in scope因为 iOS 上不存在 NSGraphicsContext。我尝试使用 UIGraphicsPDFRenderer 或 UIGraphicsBeginPDFContextToData 找到等效的翻译，并使用Ray Wenderlich 教程中的一些代码，我能够创建一个新的 PDF 并使用以下代码在其上放置文本：

func createDocument(url: URL) -> Data {
    
    //let pdfData = try? Data.init(contentsOf: url)
    
    // 1
    let pdfMetaData = [
        kCGPDFContextCreator: "Timecard App",
        kCGPDFContextAuthor: "Timecard App"
    ]
    let format = UIGraphicsPDFRendererFormat()
    format.documentInfo = pdfMetaData as [String: Any]
    
    // 2
    let pageWidth = 8.5 * 72.0
    let pageHeight = 11 * 72.0
    let pageRect = CGRect(x: 0, y: 0, width: pageWidth, height: pageHeight)
    
    // 3
    let renderer = UIGraphicsPDFRenderer(bounds: pageRect, format: format)
    
    // 4
    let data = renderer.pdfData { (context) in
        // 5
        context.beginPage()
        // 6
        let attributes = [
            NSAttributedString.Key.font: UIFont.boldSystemFont(ofSize: 72)
        ]
        let text = "I'm a PDF!"
        text.draw(at: CGPoint(x: 0, y: 0), withAttributes: attributes)
    }
    
    return data
}

...但我找不到一种方法将当前的 PDF“数据”加载到渲染器，然后从那里进行绘制。有人对执行此操作的正确方法有任何建议吗？

Answer 1

这是可能的解决方案 - 实际上你只需要直接操作 CoreGraphics 上下文，设置当前，翻转变换等（保留原始代码的样式和约定）。

使用 Xcode 12 / iOS 14 进行测试。

func executeContext(at srcURL: URL, to dstURL: URL) {
    
    // Confirm there is a document there
    if let doc: PDFDocument = PDFDocument(url: srcURL) {
        
        // Create a document, get the first page, and set the size of the page
        let page: PDFPage = doc.page(at: 0)!
        var mediaBox: CGRect = page.bounds(for: .mediaBox)
    
        // This is where the magic happens.  Create the drawing context on the PDF
        let context = CGContext(dstURL as CFURL, mediaBox: &mediaBox, nil)

        UIGraphicsPushContext(context!)
        context!.beginPDFPage(nil)

        // Draws the PDF into the context
        page.draw(with: .mediaBox, to: context!)
        
        let flipVertical: CGAffineTransform = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: mediaBox.size.height)
        context!.concatenate(flipVertical)

        let attributes = [
            NSAttributedString.Key.font: UIFont.boldSystemFont(ofSize: 72)
        ]
        let text = "I'm a PDF!"
        text.draw(at: CGPoint(x: 0, y: 0), withAttributes: attributes)
        
        context!.endPDFPage()
        context?.closePDF()

        UIGraphicsPopContext()
    }
}