UIGraphicsGetCurrentContext seems to return nil

Question

I'm trying to convert individual PDF pages into PNGs here, and it's worked perfectly until UIGraphicsGetCurrentContext suddenly started returning nil.

I'm trying to retrace my steps here, but I'm not quite sure that I know at which point this happened. My frame is not 0, which I see might create this problem, but other than that everything "looks" correct.

Here's the beginning of my code.

_pdf = CGPDFDocumentCreateWithURL((__bridge CFURLRef)_pdfFileUrl);
CGPDFPageRef myPageRef = CGPDFDocumentGetPage(_pdf, pageNumber);
CGRect aRect = CGPDFPageGetBoxRect(myPageRef, kCGPDFCropBox);
CGRect bRect = CGRectMake(0, 0, height / (aRect.size.height / aRect.size.width), height);
UIGraphicsBeginImageContext(bRect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);

Anybody have any idea what else might be causing the nil context?

Answer 1

It doesn't have to be called from "drawRect". you can also call it after "UIGraphicsBeginImageContext(bRect.size);"

Check in following line

UIGraphicsBeginImageContext(bRect.size);

if bRect.size is not 0,0

In my case, this was the reason why the returned context on the following line was null.

Answer 2

Are you calling UIGraphicsGetCurrentContext() inside of the drawRect method? As far as I know, it can only be called within drawRect, otherwise it will just return nil.