Swift iOS - 使用 PDFKit 和 UI 将文本叠加到 PDF 上

Swift iOS - Overlay text onto PDF with PDFKit and UI

我在 Swift 5 和 iOS 工作。我正在尝试将文本叠加到我当前拥有的 PDF 上。我实际上是在移植我从 macOS 应用程序制作的代码。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()
    }
}

drawText()函数完成了大部分需要的文本叠加,但我在它下面放了另一个“绘制”方法来测试它。

我得到一个错误 Cannot find 'NSGraphicsContext' in scope 是可以理解的,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 tutorial 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
}

...但我找不到将当前 PDF“数据”加载到渲染器然后从那里绘制的方法。有人对执行此操作的正确方法有任何建议吗?

这是可能的解决方案——实际上你只需要直接使用 CoreGraphics 上下文进行操作,设置电流,翻转变换等(保留原始代码的样式和约定)。

测试 Xcode 12 / iOS 14.

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()
    }
}

使用以下功能编辑其他页面

// add a new page
    func addPage(number: Int){
        // index is one less than document page number
        let index = number - 1
        context.endPDFPage()
        if let page = document.page(at: index) {
            context.beginPDFPage(nil)
            page.draw(with: .mediaBox, to: context)
            context.concatenate(flipVertical)
        }
    }

其中 document 是您要编辑的 PDF 文档。

然后开始编辑那个新页面。新页面的 X 和 Y 坐标再次重置为 0,0。