Remember Sidepane width after restart

CHANGELOG.md

@@ -46,6 +46,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue where the exception that there are invalid characters in filename. [#8786](https://github.com/JabRef/jabref/issues/8786)
 - When the proxy configuration removed the proxy user/password, this change is applied immediately.
 - We fixed an issue where removing several groups deletes only one of them. [#8390](https://github.com/JabRef/jabref/issues/8390)
+- We fixed an issue where the Sidepane(groups, web search and open office) width is not remembered after restarting JabRef. [#8907](https://github.com/JabRef/jabref/issues/8907)
 
 ### Removed
 

src/main/java/org/jabref/gui/JabRefFrame.java

@@ -448,8 +448,10 @@ private void initLayout() {
             @Override
             public void invalidated(Observable observable) {
                 if (mainStage.isShowing()) {
-                    setDividerPosition();
-                    observable.removeListener(this);
+                    Platform.runLater(() -> {
+                        setDividerPosition();
+                        observable.removeListener(this);
+                    });
                 }
             }
         });
@@ -472,10 +474,9 @@ private void updateSidePane() {
     }
 
     private void setDividerPosition() {
-        splitPane.setDividerPositions(prefs.getGuiPreferences().getSidePaneWidth());
         if (mainStage.isShowing() && !sidePane.getChildren().isEmpty()) {
-            dividerSubscription = EasyBind.subscribe(splitPane.getDividers().get(0).positionProperty(),
-                    position -> prefs.getGuiPreferences().setSidePaneWidth(position.doubleValue()));
+            splitPane.setDividerPositions(prefs.getGuiPreferences().getSidePaneWidth() / splitPane.getWidth());
+            dividerSubscription = EasyBind.subscribe(sidePane.widthProperty(), width -> prefs.getGuiPreferences().setSidePaneWidth(width.doubleValue()));
         }
     }