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

Question

There has been many Questions recently about drawing PDF s    Yes  you can render PDF s very easily with a UIWebView but this cant give the performance and functionality that you would expect from a good PDF viewer   You can draw a PDF page to a CALayer or  to a UIImage  Apple even have sample code to show how draw a large PDF in a Zoomable UIScrollview  But the same issues keep cropping up   UIImage Method    PDF s in a UIImage don t optically scale as well as a Layer approach  The CPU and memory hit on generating the UIImages from a PDFcontext limits prevents using it to create a real-time render of new zoom-levels    CATiledLayer Method    Theres a significant Overhead  time  drawing a full PDF page to a CALayer  individual tiles can be seen rendering  even with a tileSize tweak  CALayers cant be prepared ahead  of     time  rendered off-screen     Generally PDF viewers are pretty heavy on memory too  Even monitor the memory usage of apple s zoomable PDF example   In my current project  I m developing a PDF viewer and am rendering a UIImage of a page in a separate thread  issues here too   and presenting it while the scale is x1  CATiledLayer rendering kicks in once the scale is  1   iBooks takes a similar double take approach as if you scroll the pages you can see a lower res version of the page for just less than a second before a crisp version appears   Im rendering 2 pages each side of the page in focus so that the PDF image is ready to mask the layer before it starts drawing Pages are destroyed again when they are  2 pages away from the focused page   Does anyone have any insights  no matter how small or obvious to improve the performance  memory handling of Drawing PDF s  or any other issues discussed here   EDIT  Some Tips  Credit- Luke Mcneice VdesmedT Matt Gallagher Johann     Save any media to disk when you can  Use larger tileSizes if rendering on TiledLayers init frequently used arrays with placeholder objects  alternitively another design approach is this one Note that images will render faster than a CGPDFPageRef Use NSOperations or GCD  amp  Blocks to prepare pages ahead of time  call CGContextSetInterpolationQuality ctx  kCGInterpolationHigh   CGContextSetRenderingIntent ctx  kCGRenderingIntentDefault   before CGContextDrawPDFPage to reduce memory usage while drawing  init ing your NSOperations with a docRef is a bad idea  memory   wrap the docRef into a singleton  Cancel needless NSOperations When you can  especially if they will be using memory  beware of leaving contexts open though  Recycle page objects and destroy unused views Close any open Contexts as soon as you don t need them on receiving memory warnings release and reload the DocRef and any page Caches   Other PDF Features    Getting Links inside a PDF  and here and here    Understanding the PDF Rect for link positioning Converting PDF annot datestrings Getting the target of the link  Getting the page number from the  Dest array   Getting a table of contents Document title and Keywords Getting Raw Text  and here and Here and here  positioning focused   Searching and here   doesn t work with all PDFs  some just show weird characters  I guess it s an encoding issue but I m not sure  -Credit BrainFeeder  CALayer and Off-Screen Rendering - render the next page for fast smooth display   Documentation   Quartz PDFObjects  Used for meta info  annotations  thumbs   Abobe PDF Spec    Example projects   Apple  ZoomingPDF - zooming  UIScrollView  CATiledLayer vfr  reader - zooming  paging  UIScrollView  CATiledView brow  leaves - paging with nice transitions    skim - everything it seems  PDF reader editor for OSX

User · Answer

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

User · Answer

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  amp  amp  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

User · Answer

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    lt QuickLook QuickLook h gt    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

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

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