Has anyone implemented an Undo-Redo feature in PDFView control.
I am wondering how big an undertaking this feature will be, if there
is a pecific place to look at example code?
PDFView control is not doing any page editing, so there is no need for
undo/redo methods. Instead all drawing and editing would be done on
top of the page where you can use your own data-structures and where
you can implement your own undo/redo methods.
Keep in mind that you would probably not modify the PDF page/document
until the user decides to save the document (as shown in PDFView C#
markup example), so there is no need for a built-in undo/redo
mechanism on the SDK level.
There are several design patterns on how to implement undo/redo
mechanism (you may want to search for 'Command Pattern' on the Net).
Since you have full control over how you create and draw annotation
any of these approaches can be used to implement undo/redo.