Making a filter - Part 3

Our goal in this series of posts is to make a filter which extracts text from PDF file. This is going to be far simpler than you might have thought. In fact, we are using PDFDocument class in Quartz framework to read in PDF content.

PDFDocument is a newly introduced class in Tiger. This class sugar-wraps tons of code that would be necessary to render PDF file. For our PDF filter, we only need the following 2 methods of the class:

- (id)initWithData:(NSData *)data
- (NSString *)string

For detailed information about PDFDocument class, go visit the ADC Reference Library. Now, using the above methods, our unarchiveFilter:context: method will be something like this:

- (NSMutableData *)unarchiveFilter:(NSMutableData *)data context:(NSDictionary **)context
{
    PDFDocument *document = [[[PDFDocument alloc] initWithData:data] autorelease];
    return [[[[document string] dataUsingEncoding:NSUnicodeStringEncoding] mutableCopy] autorelease];
}

On the other hand, we will not do anything in archiveFilter:context: method just because it does not make sense writing the content to PDF without layout information. So this method should look like:

- (NSMutableData *)archiveFilter:(NSMutableData *)data context:(NSDictionary *)context
{
    return data;
}

The other two methods will also be defined in the same way. If you want a challenge, you can help yourself arrange them to bring some fancy format for the content.

Part 4 is going to be the last of this series. We will see how this simple filter works with AppleTrans.