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Supporting PDF documents

The Readium toolkit relies on third-party PDF engines to parse and render PDF documents.

If you want to support PDF in your application, you need to explicitly enable one of the provided PDF adapters. Instructions for each adapter are available under the readium/adapters directory.

The Test App currently showcases the pdfium adapter.

Creating an adapter for a custom PDF engine

If you wish to integrate another third-party engine with Readium, you can create your own adapter. Each PDF adapter is split in two independent components:

  • document which is required by the Streamer for parsing a PDF publication and extracting its metadata.
  • navigator which can be used with the navigator's PdfNavigatorFragment to render a PDF document.

Take a look at the existing adapters for an example implementation. The pspdfkit one is the best example.

document adapter

You will need to implement two interfaces from readium-shared:

  • PdfDocument which represents a single PDF document and provides access to its metadata and cover.
  • PdfDocumentFactory which is responsible for parsing a PDF document and creating instances of your PdfDocument implementation.

Then, you can provide your implementation to the Streamer during initialization:

val streamer = Streamer(context,
    pdfFactory = CustomDocumentFactory()
)

val publication = streamer.open(FileAsset(pdfFile)).getOrThrow()

navigator adapter

If you want to render a PDF document with readium-navigator, you can use PdfNavigatorFragment which handles most of the grunt work. You will still need to implement a few interfaces :

  • Configurable.Preferences and Configurable.Settings which will deal with the settings supported by your PDF engine.
  • PdfDocumentFragment which renders a single PDF document.
  • PreferencesEditor which enables you to easily build a user interface for your preferences.
  • VisualNavigator.Presentation which enables the navigator to get the information it needs about the current presentation, on the basis of the current settings or not.
  • PdfEngineProvider which ties everything together for the use of the PdfNavigatorFactory.

Take care of calling the Listener callbacks of PdfDocumentFragment when the user scrolls or interacts with the document and PdfNavigatorFragment will automatically send Locator progression events to the application. The input parameter will contain:

  • publication and link, to get access to the PDF resource using publication.get(link).
  • initialPageIndex which is the page index (from 0) that should be restored when creating the PDF view.
  • listener which holds the callbacks.

Finally, provide an instance of your implementation of PdfEngineProvider when initializing the PdfNavigatorFactory:

val navigatorFactory = PdfNavigatorFactory(
    publication = publication,
    pdfEngineProvider = CustomPdfEngineProvider()
)