How to change the background color of CGPDFPageRef, and how to remove the page's shadow

Question

I'm trying to draw content in a UIWebView instead of a UIView, because I like UIWebView's ability to zoom in and out by pinching. Here's my code:

// setup environment
CGRect outputRect = myWebView.bounds;
CFMutableDataRef data = CFDataCreateMutable(NULL, 0); // init with default allocator and unlimited size
CGDataConsumerRef dataConsumer = CGDataConsumerCreateWithCFData(data);
CGContextRef pdfContext = CGPDFContextCreate(dataConsumer, &outputRect, NULL);

CGPDFContextBeginPage(pdfContext, NULL);

// draw something
CGContextSetRGBFillColor (pdfContext, 1, 0, 0, 1);
CGContextFillRect (pdfContext, CGRectMake (0, 0, 200, 100 ));
CGContextSetRGBFillColor (pdfContext, 0, 0, 1, .5);
CGContextFillRect (pdfContext, CGRectMake (0, 0, 100, 200 ));

CGPDFContextEndPage(pdfContext);

// load drawing in webView
[myWebView loadData:(NSData *)data MIMEType:@"application/pdf" textEncodingName:@"utf-8" baseURL:nil];

// cleanup
if(data != NULL) CFRelease(data); // always make sure to not pass NULL in CFRelease
CGDataConsumerRelease(dataConsumer);
CGContextRelease(pdfContext);

Behind the UIWebView there other things going on which I want visible, so I have made the UIWebView's background transparent like so:

myWebView.opaque = NO; //otherwise setting background color has no effect
myWebView.backgroundColor = [UIColor clearColor];

This works correctly if I don't load the pdf. However when the pdf loads, its page has a white background and a shadow, like in the screenshot below. This is messing up my UI design. How can I get rid of the shadow and make the pdf page transparent?

Thanks

Answer 1

UIWebView uses a internal framework to display pdf's, one that doesn't let you change the background, at least not with some crazy subclassing hackery. And you really shouldn't mess around with UIWebView's internals. And you really, really shouldn't draw custom content into a UIWebView! It's absolutely not designed for that. It's designed to be treated as a black box that displays web content, and (by the mercy of god) pdf.

Use a UIScrollView and draw your pdf's there. It's not much magic and it's designed to allow zooming. For the zoom to be effective, you might wanna use a CATiledLayer to re-draw the pdf page once the user has zoomed, else the text will get blurry.

Disclaimer: I spend about a year writing PSPDFKit, a library that does just that. It's actually quite hard to make it fast and also don't crash on older devices.

When I look at your code again, do you need pdf at all? Why not just draw into a UIView that is a subview of a UIScrollView? Should work perfectly for your needs. Will also be much faster than all the way writing/parsing/rendering a pdf only to draw.