Fix document viewer not showing first page

CHANGELOG.md

@@ -75,6 +75,7 @@ inserting new citations in a OpenOffic/LibreOffice document. [#6957](https://git
 - We fixed an issue where the EndNote XML Import would fail on empty keywords tags [forum#2387](https://discourse.jabref.org/t/importing-in-unknown-format-fails-to-import-xml-library-from-bookends-export/2387)
 - We fixed an issue where the color of groups of type "free search expression" not persisting after restarting the application [#6999](https://github.com/JabRef/jabref/issues/6999)
 - We fixed an issue where modifications in the source tab where not saved without switching to another field before saving the library [#6622](https://github.com/JabRef/jabref/issues/6622)
+- We fixed an issue where the "Document Viewer" did not show the first page of the opened pdf document and did not show the correct total number of pages [#7108](https://github.com/JabRef/jabref/issues/7108)
 
 ### Removed
 

src/main/java/org/jabref/gui/documentviewer/DocumentViewerViewModel.java

@@ -5,6 +5,7 @@
 import java.util.List;
 import java.util.Objects;
 
+import javafx.application.Platform;
 import javafx.beans.property.BooleanProperty;
 import javafx.beans.property.IntegerProperty;
 import javafx.beans.property.ListProperty;
@@ -55,9 +56,11 @@ public DocumentViewerViewModel(StateManager stateManager) {
             }
         });
 
-        maxPages.bindBidirectional(
+        // we need to wrap this in run later so that the max pages number is correctly shown
+        Platform.runLater(() -> {
+            maxPages.bindBidirectional(
                 EasyBind.wrapNullable(currentDocument).selectProperty(DocumentViewModel::maxPagesProperty));
-
+        });
         setCurrentEntries(this.stateManager.getSelectedEntries());
     }
 

src/main/java/org/jabref/gui/documentviewer/PdfDocumentPageViewModel.java

@@ -60,7 +60,7 @@ public Image render(int width, int height) {
 
     @Override
     public int getPageNumber() {
-        return pageNumber;
+        return pageNumber + 1;
     }
 
     @Override

src/main/java/org/jabref/gui/documentviewer/PdfDocumentViewModel.java

@@ -26,7 +26,7 @@ public ObservableList<DocumentPageViewModel> getPages() {
         List<PdfDocumentPageViewModel> pdfPages = new ArrayList<>();
         // There is apparently no neat way to get the page number from a PDPage...thus this old-style for loop
         for (int i = 0; i < pages.getCount(); i++) {
-            pdfPages.add(new PdfDocumentPageViewModel(pages.get(i), i + 1, document));
+            pdfPages.add(new PdfDocumentPageViewModel(pages.get(i), i, document));
         }
         return FXCollections.observableArrayList(pdfPages);
     }