UIImagePNGRepresentation writeToFile can errors be catched? - ios

Question

i render Thumbnails of newly recieved PDF Document to the Documents-Directory.
I'm using the following code:
CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("thedoc.pdf"), NULL, NULL);
CGPDFDocumentRef bookPDF = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
UIGraphicsBeginImageContext(CGSizeMake(100, 130));
NSUInteger totalNum = CGPDFDocumentGetNumberOfPages(bookPDF);
CGContextRef context = UIGraphicsGetCurrentContext();
for(int i = 0; i < totalNum; i++ ) {
CGRect arect = CGRectMake(0,0,200,282);
CGContextSaveGState(context);
CGContextTranslateCTM(context, 0.0, 141);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextSetGrayFillColor(context, 1.0, 1.0);
CGContextFillRect(context, arect);
// Grab the first PDF page
CGPDFPageRef page = CGPDFDocumentGetPage(bookPDF, i + 1);
CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFMediaBox, arect, 0, true);
// And apply the transform.
CGContextConcatCTM(context, pdfTransform);
CGContextDrawPDFPage(context, page);
// Create the new UIImage from the context
UIImage* thumbnailImage = UIGraphicsGetImageFromCurrentImageContext();
if (thumbnailImage == nil) {
NSLog(#"ERROR during creation of PNG");
}
// SAVE THE IMAGE TO DOCUMENTS-DIRECTORY
NSString *pngPath = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:#"%#/thumbPage%i.png",theLocalFolder ,i]];
// Write image to PNG
BOOL writtenBool = [UIImagePNGRepresentation(thumbnailImage) writeToFile:pngPath atomically:YES];
// END SAVE THE IMAGE TO DOCUMENT-DIRECTORY
CGContextRestoreGState(context);
NSLog(#"Rendering PDF-Thumbnail %i (%i): %#", i, writtenBool, [NSString stringWithFormat:#"%#/thumbPage%i.png",theLocalFolder ,i]);
}
There is no error in Console, but the PNGs are not stored to the documents-Directory. The BOOL
writtenBool
is "0", what means that the write-action was not succuessful. I don't know why. I write the path in
pngPath
also to the console and the path is correct. If i open a terminal and write
open <<copyed path from console>>
it opens the correct path in finder.
What could cause this not to work? I had a look at the api but there seems to be no
error:
for UIImagePNGRepresentation: writeToFile:
Thanks for your help!

Answer 1

UIImagePNGRepresentation(thumbnailImage) return a NSData object
for NSData object, you can use these methods:
writeToFile:atomically:,
writeToFile:options:error:,
writeToURL:atomically:,
writeToURL:options:error:,
so, you can try use code like BOOL writtenBool = [UIImagePNGRepresentation(thumbnailImage) writeToFile:pngPath options:NSDataWritingAtomic error:&error]; to see what happened.