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Undo / redo edits to a PDF file using Go

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The PDFTron SDK has a low-level facility for undo and redo operations. It is a API that applies to any edits made to a particular document (not just annotations). This sample Go code shows how to use PDFTron SDK to walk back and forth on a fully general, bit-exact list of document states. Saving changes in a mode that is not 'incremental' will wipe out the undo-redo state list; the API will not be able to access old snapshots anymore. See the undoing and redoing guide for more information. Learn more about our Go PDF Library.

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//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2021 by PDFTron Systems Inc. All Rights Reserved.
// Consult LICENSE.txt regarding license information.
//---------------------------------------------------------------------------------------

package main
import (
    "fmt"
	. "pdftron"
)

import  "pdftron/Samples/LicenseKey/GO"

// Relative path to the folder containing test files.
var inputPath =  "../../TestFiles/"
var outputPath = "../../TestFiles/Output/"

//---------------------------------------------------------------------------------------
// The following sample illustrates how to use the UndoRedo API.
//---------------------------------------------------------------------------------------

func main(){
    // The first step in every application using PDFNet is to initialize the 
    // library and set the path to common PDF resources. The library is usually 
    // initialized only once, but calling Initialize() multiple times is also fine.
    PDFNetInitialize(PDFTronLicense.Key)
    
    // Open the PDF document.
    doc := NewPDFDoc(inputPath + "newsletter.pdf")

    undoManager := doc.GetUndoManager()

    // Take a snapshot to which we can undo after making changes.
    snap0 := undoManager.TakeSnapshot()

    snap0State := snap0.CurrentState()
    
    // Start a new page
    page := doc.PageCreate()

    bld := NewElementBuilder()          // Used to build new Element objects
    writer := NewElementWriter()        // Used to write Elements to the page
    writer.Begin(page)              // Begin writing to this page

    // ----------------------------------------------------------
    // Add JPEG image to the file
    img := ImageCreate(doc.GetSDFDoc(), inputPath + "peppers.jpg")

    element := bld.CreateImage(img, NewMatrix2D(200.0, 0.0, 0.0, 250.0, 50.0, 500.0))
    writer.WritePlacedElement(element)

    // Finish writing to the page
    writer.End()
    doc.PagePushFront(page)

    // Take a snapshot after making changes, so that we can redo later (after undoing first).
    snap1 := undoManager.TakeSnapshot()

    if snap1.PreviousState().Equals(snap0State){
        fmt.Println("snap1 previous state equals snap0State; previous state is correct")
    }    
    snap1State := snap1.CurrentState()

    doc.Save(outputPath + "addimage.pdf", uint(SDFDocE_incremental))

    if undoManager.CanUndo(){
        undoSnap := undoManager.Undo()

        doc.Save(outputPath + "addimage_undone.pdf", uint(SDFDocE_incremental))

        undoSnapState := undoSnap.CurrentState()

        if undoSnapState.Equals(snap0State){
            fmt.Println("undoSnapState equals snap0State; undo was successful")
        }

        if undoManager.CanRedo(){
            redoSnap := undoManager.Redo()

            doc.Save(outputPath + "addimage_redone.pdf", uint(SDFDocE_incremental))

            if redoSnap.PreviousState().Equals(undoSnapState){
                fmt.Println("redoSnap previous state equals undoSnapState; previous state is correct")
            }

            redoSnapState := redoSnap.CurrentState()
            
            if redoSnapState.Equals(snap1State){
                fmt.Println("Snap1 and redoSnap are equal; redo was successful")
            }
        }else{
            fmt.Println("Problem encountered - cannot redo.")
        }
    }else{
        fmt.Println("Problem encountered - cannot undo.")
    }
    PDFNetTerminate()
}

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