Swift iOS-使用PDFKit和UI将文本覆盖到PDF

问题描述

我正在使用Swift 5和iOS。我正在尝试将文本覆盖到当前的PDF上。我实质上是在移植从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()函数完成了大多数所需的文本叠加，但是我在其下面放置了另一种“绘制”方法来进行测试。

我可以理解的是，由于iOS上不存在NSGraphicsContext，因此出现了一个错误Cannot find 'NSGraphicsContext' in scope。我试图用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,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,withAttributes: attributes)
    }
    
    return data
}

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

解决方法

这里是可能的解决方案-实际上，您只需要直接与CoreGraphics上下文一起操作，设置当前值，进行翻转变换等即可（保留原始代码的样式和约定）。

通过Xcode 12 / iOS 14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()
    }
}