Item Count in a group updated correctly (#4807)

* Item Count in a group updated correctly

* Added comments

* changes

src/main/java/org/jabref/gui/groups/GroupNodeViewModel.java

@@ -55,6 +55,7 @@ public class GroupNodeViewModel {
     private final BooleanBinding allSelectedEntriesMatched;
     private final TaskExecutor taskExecutor;
     private final CustomLocalDragboard localDragBoard;
+    private final ObservableList<BibEntry> entriesList;
 
     public GroupNodeViewModel(BibDatabaseContext databaseContext, StateManager stateManager, TaskExecutor taskExecutor, GroupTreeNode groupNode, CustomLocalDragboard localDragBoard) {
         this.databaseContext = Objects.requireNonNull(databaseContext);
@@ -84,7 +85,9 @@ public GroupNodeViewModel(BibDatabaseContext databaseContext, StateManager state
         expandedProperty.addListener((observable, oldValue, newValue) -> groupNode.getGroup().setExpanded(newValue));
 
         // Register listener
-        databaseContext.getDatabase().getEntries().addListener(this::onDatabaseChanged);
+        // The wrapper created by the FXCollections will set a weak listener on the wrapped list. This weak listener gets garbage collected. Hence, we need to maintain a reference to this list.
+        entriesList = databaseContext.getDatabase().getEntries();
+        entriesList.addListener(this::onDatabaseChanged);
 
         ObservableList<Boolean> selectedEntriesMatchStatus = EasyBind.map(stateManager.getSelectedEntries(), groupNode::matches);
         anySelectedEntriesMatched = BindingsHelper.any(selectedEntriesMatchStatus, matched -> matched);