How to add the metadata to a pdf in Objective C?

How to add the metadata to a pdf in Objective C? I came across a class method called CGPDFContextAddDocumentMetadata, but could not find a开发者_JS百科ny documentation of how to achieve it.

The metadata that can be added with this method is XMP metadata. It is XML based and looks like this (it is fully documented here: http://www.adobe.com/products/xmp/):

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 4.2.1-c041">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" >
<rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
  <dc:format>application/pdf</dc:format>
  <dc:title>
    <rdf:Alt>
      <rdf:li />
    </rdf:Alt>
  </dc:title>
  <dc:description>
    <rdf:Alt>
      <rdf:li />
    </rdf:Alt>
  </dc:description>
  <dc:creator>
    <rdf:Seq>
      <rdf:li />
    </rdf:Seq>
  </dc:creator>
</rdf:Description>
<rdf:Description rdf:about="" xmlns:pdf="http://ns.adobe.com/pdf/1.3/">
  <pdf:Keywords />
  <pdf:Producer />
</rdf:Description>
<rdf:Description rdf:about="" xmlns:xmp="http://ns.adobe.com/xap/1.0/">
  <xmp:CreatorTool />
  <xmp:CreateDate>2011-02-10T11:41:05+02:00</xmp:CreateDate>
  <xmp:ModifyDate>2011-02-10T11:41:06+02:00</xmp:ModifyDate>
</rdf:Description></rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>

The method looks like this:

void CGPDFContextAddDocumentMetadata(CGContextRef context,CFDataRef metadata);

'context' is your pdf context, metadata is your XMP metadata. You can construct the metadata in a NSString object (xmpString variable below) and then convert the NSString to CFDataRef:

CFDataRef xmpDataRef = (CFDataRef)[xmpString dataUsingEncoding:NSUTF8StringEncoding];