PDFKit - PDFView using pageViewController - page rendering slow when swiping to next page

Question

I have a PDFView that's set to use a pageViewController:

    let pdfView = PDFView()
    let pdfDoc = PDFDocument(url: Bundle.main.url(forResource: "test", withExtension: "pdf")!)
    pdfView.document = pdfDoc
    pdfView.autoScales = true
    pdfView.displayDirection = .horizontal
    pdfView.usePageViewController(true, withViewOptions: [:])

Whenever I swipe to get to the next page, said next page is blurry for half a second before it's rendered sharply. That is quite annoying. Can I somehow preload the pages? I haven't found any attributes/methods in the documentation.

(Interestingly, I have the exact same problem in Preview on MacOS when it's in fullscreen mode [since forever, on every mac I own])

It's not reliant on pdf (file) size. The problem occurs with every pdf I tried.

Thanks for any help

Answer 1

I think this is due to the high resolution of your PDF and the way PDFView renders PDF. Do you have more information on your PDF?

Could you try with a PDF with less heavy images? It should render fine. If so, it's not your code which is at fault, but the resources needed to display and render it to the view.

UPDATE

You can try using the PDFView without PageViewController and see you it behaves. You could do this:

pdfView = PDFView(frame: view.frame)
pdfView.backgroundColor = UIColor.white

var documentName: String = "test"

if let documentURL = Bundle.main.url(forResource: documentName, withExtension: "pdf") {
    if let document = PDFDocument(url: documentURL) {
        pdfView.autoScales = true
        pdfView.displayDirection = .horizontal
        pdfView.displayMode = .singlePageContinuous
        pdfView.document = document
    }
}

self.view.addSubview(pdfView)

Does it behave differently? I've notice that the option usePageViewController loads the document faster for big PDF documents. Something to take into consideration when implementing.

I hope this helps

Answer 2

Please make sure to add values of .maxScaleFactor .minScaleFactor also as per your requirement and see if it makes any difference in the loading time. e.g.

.maxScaleFactor = 4.0;
.minScaleFactor = self.scaleFactorForSizeToFit;