Getting notifications when PDF documents are modified in qPDF Toolkit

A: I am using QPDFNotesView within qPDF Toolkit to display, annotate and fill PDF forms in Android. Is there a mechanism that allows to be notified when a PDF document has been changed, for instance when a form field has been updated?

A: Yes, this is possible by adding a DocumentListener, see sample code below.

Document events for which you can receive notifications are the following:
ANNOT_REMOVED, ANNOTATION_ADDED, ANNOTATION_MODIFIED, ANNOTATIONS_IMPORTED, ATTACH_ADDED, ATTACH_REMOVED, BOOKMARK_CHANGED, BOOKMARK_CREATED, DOCUMENT_CHANGED, INSERT_LAYER, PAGE_ADDED, PAGE_CONTENT_CHANGED, PAGE_MOVED, PAGE_REMOVED, PAGE_SIZE_CHANGED, PAGEANNOTS_REMOVED, PAGEFIELDS_FLATTENED, WIDGET_UPDATED.

public class MyActivity extends Activity 
{
   public QPDFNotesView notes;
 
   protected void onCreate(Bundle bundle)
   {
      super.onCreate(bundle);
 
      notes = new QPDFNotesView(this);
      notes.setActivity(this);
      setContentView(notes);
 
      notes.addDocumentListener(new DocumentListener() {
 
     @Override
         public void documentOpened() {
 
            // When a document is opened, add a listener to listen for changes
            notes.getDocument().addDocumentListener(new DocumentChangeListener() {
 
               // Document Changed Event
               @Override
               public void documentChanged(DocumentEvent de) {
                  if (de.getEventType() == DocumentEvent.WIDGET_UPDATED)
                  {
                     // code to do something after the field's value has changed
                  }
               }
            });
         }
 
         @Override
         public void documentSaved(String previousPath) {}
 
         @Override
         public void zoomChanged(float zoom) {}
      });
   }
}