iOS PDF Rendering runs out of memory

Question

I'm using the following code to render about a 100 pages to a pdf in an iOS App, basically creating screenshots of the app's contents:

...
UIGraphicsBeginPDFContextToFile(mainPath, currentFrame, nil);
for(Page *page in pages)
{
  @autoreleasepool
  {
    MainViewController *viewCtrl = [[MainViewController alloc] initWithPage:page contentController:[ContentController singleton] inBackground:NO];
    [self createPageWithView:viewCtrl.view];
  }
}
UIGraphicsEndPDFContext();



-(void)createPageWithView:(UIView *)view
{
  DLog(@"creating page...");
  UIGraphicsBeginImageContextWithOptions(view.bounds.size, NO, 0.0);
  [view.layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  UIGraphicsBeginPDFPageWithInfo(currentFrame, nil);
  CGContextRef pdfContext = UIGraphicsGetCurrentContext();

  UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
  [imageView.layer renderInContext:pdfContext];
}

This runs out of memory somewhere midways. The mainviewController adds a couple subviews, nothing special. Why is this happening? Shouldnt the autoreleasepool clean up the used memory?

Answer 1

The PDF file is created entirely in memory and written to disk when UIGraphicsEndPDFContext is called. This causes memory problems if the PDF file is getting very large.