is it possible to access pdf outline when developing for iOS

问题

being that PDFKit is not available on iOS, how is it possible to get the outline of a pdf document in that environment? Is commercial libraries like FastPdfKit or PSPDFKit the only solution?

回答1:

It's not TOO tricky to access the pdf outline. My outline parser has about 420 LOC. I'll post some snippets, so you'll get the idea. I can't post the full code as it's a commercial library.

You basically start like this:

CGPDFDictionaryRef outlineRef;
if(CGPDFDictionaryGetDictionary(pdfDocDictionary, "Outlines", &outlineRef)) {

going down to

NSArray *outlineElements = nil;
CGPDFDictionaryRef firstEntry;
if (CGPDFDictionaryGetDictionary(outlineRef, "First", &firstEntry)) {
    NSMutableArray *pageCache = [NSMutableArray arrayWithCapacity:CGPDFDocumentGetNumberOfPages(documentRef)];
    outlineElements = [self parseOutlineElements:firstEntry level:0 error:&error documentRef:documentRef cache:pageCache];
}else {
    PSPDFLogWarning(@"Error while parsing outline. First entry not found!");
}

you parse single items like this:

// parse title
NSString *outlineTitle = stringFromCGPDFDictionary(outlineElementRef, @"Title");
PSPDFLogVerbose(@"outline title: %@", outlineTitle);
if (!outlineTitle) {
    if (error_) {
        *error_ = [NSError errorWithDomain:kPSPDFOutlineParserErrorDomain code:1 userInfo:nil];
    }
    return nil;
}

NSString *namedDestination = nil;
CGPDFObjectRef destinationRef;
if (CGPDFDictionaryGetObject(outlineElementRef, "Dest", &destinationRef)) {
    CGPDFObjectType destinationType = CGPDFObjectGetType(destinationRef);

The most annoying thing is that you have Named Destinations in most pdf documents, which need additional steps to resolve. I save those in an array and resolve them later.

It took quite a while to "get it right" as there are LOTS of differences in the PDFs that are around, and even if you implement everything in compliance to the PDF reference, some files won't work until you apply further tweaking. (PDF is a mess!)