Fast and Lean PDF Viewer for iPhone / iPad / iOS - tips and hints?

I have build such kind of application using approximatively the same approach except :

• I cache the generated image on the disk and always generate two to three images in advance in a separate thread.
• I don't overlay with a UIImage but instead draw the image in the layer when zooming is 1. Those tiles will be released automatically when memory warnings are issued.

Whenever the user start zooming, I acquire the CGPDFPage and render it using the appropriate CTM. The code in - (void)drawLayer: (CALayer*)layer inContext: (CGContextRef) context is like :

CGAffineTransform currentCTM = CGContextGetCTM(context);    if (currentCTM.a == 1.0 && baseImage) {    //Calculate ideal scale    CGFloat scaleForWidth = baseImage.size.width/self.bounds.size.width;    CGFloat scaleForHeight = baseImage.size.height/self.bounds.size.height;     CGFloat imageScaleFactor = MAX(scaleForWidth, scaleForHeight);    CGSize imageSize = CGSizeMake(baseImage.size.width/imageScaleFactor, baseImage.size.height/imageScaleFactor);    CGRect imageRect = CGRectMake((self.bounds.size.width-imageSize.width)/2, (self.bounds.size.height-imageSize.height)/2, imageSize.width, imageSize.height);    CGContextDrawImage(context, imageRect, [baseImage CGImage]);} else {    @synchronized(issue) {         CGPDFPageRef pdfPage = CGPDFDocumentGetPage(issue.pdfDoc, pageIndex+1);        pdfToPageTransform = CGPDFPageGetDrawingTransform(pdfPage, kCGPDFMediaBox, layer.bounds, 0, true);        CGContextConcatCTM(context, pdfToPageTransform);            CGContextDrawPDFPage(context, pdfPage);    }}

issue is the object containg the CGPDFDocumentRef. I synchronize the part where I access the pdfDoc property because I release it and recreate it when receiving memoryWarnings. It seems that the CGPDFDocumentRef object do some internal caching that I did not find how to get rid of.

For a simple and effective PDF viewer, when you require only limited functionality, you can now (iOS 4.0+) use the QuickLook framework:

First, you need to link against QuickLook.framework and #import <QuickLook/QuickLook.h>;

Afterwards, in either viewDidLoad or any of the lazy initialization methods:

QLPreviewController *previewController = [[QLPreviewController alloc] init];previewController.dataSource = self;previewController.delegate = self;previewController.currentPreviewItemIndex = indexPath.row;[self presentModalViewController:previewController animated:YES];[previewController release];

Since iOS 11, you can use the native framework called PDFKit for displaying and manipulating PDFs.

After importing PDFKit, you should initialize a PDFView with a local or a remote URL and display it in your view.

if let url = Bundle.main.url(forResource: "example", withExtension: "pdf") {    let pdfView = PDFView(frame: view.frame)    pdfView.document = PDFDocument(url: url)    view.addSubview(pdfView)}

Read more about PDFKit in the Apple Developer documentation.