Add drag and drop in EntryEditor

CHANGELOG.md

@@ -26,6 +26,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We added the possibility to automatically fetch entries when an ISBN is pasted on the main table. [#9864](https://github.com/JabRef/jabref/issues/9864)
 - We added the option to disable the automatic linking of files in the entry editor [#5105](https://github.com/JabRef/jabref/issues/5105)
 - We added the link icon for ISBNs in linked identifiers column. [#9819](https://github.com/JabRef/jabref/issues/9819)
+- We added drag and drop events for field 'Groups' in entry editor panel. [#569](https://github.com/koppor/jabref/issues/569)
 - We added support for parsing MathML in the Medline importer. [#4273](https://github.com/JabRef/jabref/issues/4273)
 
 ### Changed

src/main/java/org/jabref/gui/fieldeditors/FieldEditors.java

@@ -67,6 +67,8 @@ public static FieldEditorFX getForField(final Field field,
             return new IdentifierEditor(field, taskExecutor, dialogService, suggestionProvider, fieldCheckers, preferences);
         } else if (field == StandardField.OWNER) {
             return new OwnerEditor(field, preferences, suggestionProvider, fieldCheckers);
+        } else if (field == StandardField.GROUPS) {
+            return new GroupEditor(field, suggestionProvider, fieldCheckers, preferences, isMultiLine);
         } else if (fieldProperties.contains(FieldProperty.FILE_EDITOR)) {
             return new LinkedFilesEditor(field, dialogService, databaseContext, taskExecutor, suggestionProvider, fieldCheckers, preferences);
         } else if (fieldProperties.contains(FieldProperty.YES_NO)) {

src/main/java/org/jabref/gui/fieldeditors/GroupEditor.java

@@ -0,0 +1,57 @@
+package org.jabref.gui.fieldeditors;
+
+import java.util.List;
+import java.util.Optional;
+
+import javafx.scene.input.TransferMode;
+
+import org.jabref.gui.DragAndDropDataFormats;
+import org.jabref.gui.autocompleter.SuggestionProvider;
+import org.jabref.logic.integrity.FieldCheckers;
+import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.field.Field;
+import org.jabref.model.entry.field.StandardField;
+import org.jabref.preferences.PreferencesService;
+
+public class GroupEditor extends SimpleEditor {
+
+    private Optional<BibEntry> bibEntry;
+
+    public GroupEditor(final Field field,
+                       final SuggestionProvider<?> suggestionProvider,
+                       final FieldCheckers fieldCheckers,
+                       final PreferencesService preferences,
+                       final boolean isMultiLine) {
+        super(field, suggestionProvider, fieldCheckers, preferences, isMultiLine);
+
+        this.setOnDragOver(event -> {
+            if (event.getDragboard().hasContent(DragAndDropDataFormats.GROUP)) {
+                event.acceptTransferModes(TransferMode.MOVE);
+            }
+            event.consume();
+        });
+
+        this.setOnDragDropped(event -> {
+            boolean success = false;
+            if (event.getDragboard().hasContent(DragAndDropDataFormats.GROUP)) {
+                List<String> draggedGroups = (List<String>) event.getDragboard().getContent(DragAndDropDataFormats.GROUP);
+                if (bibEntry.isPresent() && draggedGroups.get(0) != null) {
+                    String newGroup = bibEntry.map(entry -> entry.getField(StandardField.GROUPS)
+                                                                     .map(oldGroups -> oldGroups + (preferences.getBibEntryPreferences().getKeywordSeparator()) + (draggedGroups.get(0)))
+                                                                     .orElse(draggedGroups.get(0)))
+                                                  .orElse(null);
+                    bibEntry.map(entry -> entry.setField(StandardField.GROUPS, newGroup));
+                    success = true;
+                }
+            }
+            event.setDropCompleted(success);
+            event.consume();
+        });
+    }
+
+    @Override
+    public void bindToEntry(BibEntry entry) {
+        super.bindToEntry(entry);
+        this.bibEntry = Optional.of(entry);
+    }
+}