> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/android/get-started/samples/undoredotest.md). # UndoRedoTest Sample Java code for using Apryse SDK to take snapshots of edits and move between them using the API. The Apryse 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 Java code shows how to use Apryse 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](/core/pdf-editing/undoredo.md) for more information. Learn more about our [Android SDK](/core/get-started/languages/java.md). {% tabs %} {% tab title="Java" %} {% code lineNumbers="true" %} ```java package com.pdftron.android.pdfnetsdksamples.samples;//--------------------------------------------------------------------------------------- // Copyright (c) 2001-2019 by PDFTron Systems Inc. All Rights Reserved. // Consult legal.txt regarding legal and license information. //--------------------------------------------------------------------------------------- import com.pdftron.android.pdfnetsdksamples.OutputListener; import com.pdftron.android.pdfnetsdksamples.PDFNetSample; import com.pdftron.android.pdfnetsdksamples.R; import com.pdftron.android.pdfnetsdksamples.util.Utils; import com.pdftron.common.Matrix2D; import com.pdftron.pdf.Element; import com.pdftron.pdf.ElementBuilder; import com.pdftron.pdf.ElementWriter; import com.pdftron.pdf.Image; import com.pdftron.pdf.PDFDoc; import com.pdftron.pdf.Page; import com.pdftron.sdf.DocSnapshot; import com.pdftron.sdf.ResultSnapshot; import com.pdftron.sdf.SDFDoc; import com.pdftron.sdf.UndoManager; import java.util.ArrayList; //--------------------------------------------------------------------------------------- // The following sample illustrates how to use the UndoRedo API. //--------------------------------------------------------------------------------------- public class UndoRedoTest extends PDFNetSample { private static OutputListener mOutputListener; private static ArrayList mFileList = new ArrayList<>(); public UndoRedoTest() { setTitle(R.string.sample_undoredo_title); setDescription(R.string.sample_undoredo_description); } @Override public void run(OutputListener outputListener) { super.run(outputListener); mOutputListener = outputListener; mFileList.clear(); printHeader(outputListener); try { // 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. // Open the PDF document. try (PDFDoc doc = new PDFDoc(Utils.getAssetTempFile(INPUT_PATH + "newsletter.pdf").getAbsolutePath())) { UndoManager undo_manager = doc.getUndoManager(); // Take a snapshot to which we can undo after making changes. ResultSnapshot snap0 = undo_manager.takeSnapshot(); DocSnapshot snap0_state = snap0.currentState(); Page page = doc.pageCreate(); // Start a new page ElementBuilder bld = new ElementBuilder(); // Used to build new Element objects ElementWriter writer = new ElementWriter(); // Used to write Elements to the page writer.begin(page); // Begin writing to this page // ---------------------------------------------------------- // Add JPEG image to the file Image img = Image.create(doc, Utils.getAssetTempFile(INPUT_PATH + "peppers.jpg").getAbsolutePath()); Element element = bld.createImage(img, new Matrix2D(200, 0, 0, 250, 50, 500)); writer.writePlacedElement(element); writer.end(); // Finish writing to the page doc.pagePushFront(page); // Take a snapshot after making changes, so that we can redo later (after undoing first). ResultSnapshot snap1 = undo_manager.takeSnapshot(); if (snap1.previousState().equals(snap0_state)) { mOutputListener.println("snap1 previous state equals snap0_state; previous state is correct"); } DocSnapshot snap1_state = snap1.currentState(); doc.save(Utils.createExternalFile("addimage.pdf", mFileList).getAbsolutePath(), SDFDoc.SaveMode.INCREMENTAL, null); if (undo_manager.canUndo()) { ResultSnapshot undo_snap; undo_snap = undo_manager.undo(); doc.save(Utils.createExternalFile("addimage_undone.pdf", mFileList).getAbsolutePath(), SDFDoc.SaveMode.INCREMENTAL, null); DocSnapshot undo_snap_state = undo_snap.currentState(); if (undo_snap_state.equals(snap0_state)) { mOutputListener.println("undo_snap_state equals snap0_state; undo was successful"); } if (undo_manager.canRedo()) { ResultSnapshot redo_snap = undo_manager.redo(); doc.save(Utils.createExternalFile("addimage_redone.pdf", mFileList).getAbsolutePath(), SDFDoc.SaveMode.INCREMENTAL, null); if (redo_snap.previousState().equals(undo_snap_state)) { mOutputListener.println("redo_snap previous state equals undo_snap_state; previous state is correct"); } DocSnapshot redo_snap_state = redo_snap.currentState(); if (redo_snap_state.equals(snap1_state)) { mOutputListener.println("Snap1 and redo_snap are equal; redo was successful"); } } else { mOutputListener.println("Problem encountered - cannot redo."); } } else { mOutputListener.println("Problem encountered - cannot undo."); } } // Calling Terminate when PDFNet is no longer in use is a good practice, but // is not required. } catch (Exception e) { mOutputListener.printError(e.getStackTrace()); } for (String file : mFileList) { addToFileList(file); } printFooter(outputListener); } } ``` {% endcode %} {% endtab %} {% tab title="Kotlin" %} {% code lineNumbers="true" %} ```kotlin package com.pdftron.android.pdfnetsdksamples.samples //--------------------------------------------------------------------------------------- // Copyright (c) 2001-2019 by PDFTron Systems Inc. All Rights Reserved. // Consult legal.txt regarding legal and license information. //--------------------------------------------------------------------------------------- import com.pdftron.android.pdfnetsdksamples.OutputListener import com.pdftron.android.pdfnetsdksamples.PDFNetSample import com.pdftron.android.pdfnetsdksamples.R import com.pdftron.android.pdfnetsdksamples.util.Utils import com.pdftron.common.Matrix2D import com.pdftron.pdf.ElementBuilder import com.pdftron.pdf.ElementWriter import com.pdftron.pdf.Image import com.pdftron.pdf.PDFDoc import com.pdftron.sdf.ResultSnapshot import com.pdftron.sdf.SDFDoc import java.util.* //--------------------------------------------------------------------------------------- // The following sample illustrates how to use the UndoRedo API. //--------------------------------------------------------------------------------------- class UndoRedoTest : PDFNetSample() { init { setTitle(R.string.sample_undoredo_title) setDescription(R.string.sample_undoredo_description) } override fun run(outputListener: OutputListener?) { super.run(outputListener) mOutputListener = outputListener mFileList.clear() printHeader(outputListener!!) try { // 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. // Open the PDF document. PDFDoc(Utils.getAssetTempFile(PDFNetSample.INPUT_PATH + "newsletter.pdf")!!.absolutePath).use { doc -> val undo_manager = doc.undoManager // Take a snapshot to which we can undo after making changes. val snap0 = undo_manager.takeSnapshot() val snap0_state = snap0.currentState() val page = doc.pageCreate() // Start a new page val bld = ElementBuilder() // Used to build new Element objects val writer = ElementWriter() // Used to write Elements to the page writer.begin(page) // Begin writing to this page // ---------------------------------------------------------- // Add JPEG image to the file val img = Image.create(doc, Utils.getAssetTempFile(PDFNetSample.INPUT_PATH + "peppers.jpg")!!.absolutePath) val element = bld.createImage(img, Matrix2D(200.0, 0.0, 0.0, 250.0, 50.0, 500.0)) writer.writePlacedElement(element) writer.end() // Finish writing to the page doc.pagePushFront(page) // Take a snapshot after making changes, so that we can redo later (after undoing first). val snap1 = undo_manager.takeSnapshot() if (snap1.previousState().equals(snap0_state)) { mOutputListener!!.println("snap1 previous state equals snap0_state; previous state is correct") } val snap1_state = snap1.currentState() doc.save(Utils.createExternalFile("addimage.pdf", mFileList).absolutePath, SDFDoc.SaveMode.INCREMENTAL, null) if (undo_manager.canUndo()) { val undo_snap: ResultSnapshot undo_snap = undo_manager.undo() doc.save(Utils.createExternalFile("addimage_undone.pdf", mFileList).absolutePath, SDFDoc.SaveMode.INCREMENTAL, null) val undo_snap_state = undo_snap.currentState() if (undo_snap_state.equals(snap0_state)) { mOutputListener!!.println("undo_snap_state equals snap0_state; undo was successful") } if (undo_manager.canRedo()) { val redo_snap = undo_manager.redo() doc.save(Utils.createExternalFile("addimage_redone.pdf", mFileList).absolutePath, SDFDoc.SaveMode.INCREMENTAL, null) if (redo_snap.previousState().equals(undo_snap_state)) { mOutputListener!!.println("redo_snap previous state equals undo_snap_state; previous state is correct") } val redo_snap_state = redo_snap.currentState() if (redo_snap_state.equals(snap1_state)) { mOutputListener!!.println("Snap1 and redo_snap are equal; redo was successful") } } else { mOutputListener!!.println("Problem encountered - cannot redo.") } } else { mOutputListener!!.println("Problem encountered - cannot undo.") } // Calling Terminate when PDFNet is no longer in use is a good practice, but // is not required. } } catch (e: Exception) { mOutputListener!!.printError(e.stackTrace) } for (file in mFileList) { addToFileList(file) } printFooter(outputListener) } companion object { private var mOutputListener: OutputListener? = null private val mFileList = ArrayList() } } ``` {% endcode %} {% endtab %} {% endtabs %} --- # Agent Instructions This documentation is published with GitBook. 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