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→Custom Print Adapters
In this chapter, an overview of these steps will be provided, followed by a detailed tutorial designed to demonstrate the implementation of custom document printing within Android applications.
=== Custom Custom Print Adapters ===
The role of the print adapter is to provide the Printing framework with the content to be printed, and to ensure that it is formatted correctly for the user’s chosen preferences (taking into consideration factors such as paper size and page orientation).
Custom print adapters are created by sub-classing the PrintDocumentAdapter class and overriding a set of callback methods within that class which will be called by the Printing framework at various stages in the print process. These callback methods can be summarized as follows:
* '''onStart() ''' – This method is called when the printing process begins and is provided so that the application code has an opportunity to perform any necessary tasks in preparation for creating the print job. Implementation of this method within the PrintDocumentAdapter sub-class is optional.
* '''onLayout() ''' – This callback method is called after the call to the onStart() method and then again each time the user makes changes to the print settings (such as changing the orientation, paper size or color settings). This method should adapt the content and layout where necessary to accommodate these changes. Once these changes are completed, the method must return the number of pages to be printed. Implementation of the onLayout() method within the PrintDocumentAdapter sub-class is mandatory.
* '''onWrite() ''' – This method is called after each call to onLayout() and is responsible for rendering the content on the canvases of the pages to be printed. Amongst other arguments, this method is passed a file descriptor to which the resulting PDF document must be written once rendering is complete. A call is then made to the onWriteFinished() callback method passing through an argument containing information about the page ranges to be printed. Implementation of the onWrite() method within the PrintDocumentAdapter sub-class is mandatory.
* '''onFinish() ''' – An optional method which, if implemented, is called once by the Printing framework when the printing process is completed, thereby providing the application the opportunity to perform any clean-up operations that may be necessary.
== Preparing the Custom Document Printing Project ==
