Fix(workbench): StackRenderer updates correctly when part is moved

Fixes Eclipse Bug 576186.

The StackRenderer now correctly updates its UI when a part within the stack is moved. This was achieved by handling UIEvents.isMOVE events for MPartStack children in StackRenderer.java. CTabItems, which represent tabs, cannot be reordered directly and must be disposed of and recreated at the new index. The methods calcIndexFor and findItemForPart in StackRenderer were updated to accept a more generic MElementContainer<? extends MUIElement> parameter to resolve type compatibility issues with MPartStack.

Author: vogella

bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/ui/workbench/renderers/swt/StackRenderer.java

@@ -395,6 +395,60 @@ void subscribeTopicChildrenChanged(@UIEventTopic(UIEvents.ElementContainer.TOPIC
 		shouldTopRightAdjusted(event);
 	}
 
+	@Inject
+	@Optional
+	void subscribeTopicChildrenMoved(@UIEventTopic(UIEvents.ElementContainer.TOPIC_CHILDREN) Event event) {
+		if (!UIEvents.isMOVE(event)) {
+			return;
+		}
+		// Ensure that this event is for a MPartStack
+		Object element = event.getProperty(UIEvents.EventTags.ELEMENT);
+		if (!(element instanceof MPartStack)) {
+			return;
+		}
+
+		MPartStack stack = (MPartStack) element;
+		if (stack.getRenderer() != this) {
+			return;
+		}
+
+		MUIElement movedElement = (MUIElement) event.getProperty(UIEvents.EventTags.NEW_VALUE);
+
+		CTabFolder tabFolder = (CTabFolder) stack.getWidget();
+		if (tabFolder == null || tabFolder.isDisposed()) {
+			return;
+		}
+
+		CTabItem item = findItemForPart(movedElement, stack);
+		if (item == null || item.isDisposed()) {
+			return;
+		}
+
+		int newIndex = calcIndexFor(stack, movedElement);
+
+		// Remember the control, it will be disposed with the CTabItem otherwise
+		Control control = item.getControl();
+		item.setControl(null);
+
+		// As CTabItem cannot be reordered, we need to dispose and recreate it
+		String text = item.getText();
+		Image image = item.getImage();
+		boolean showClose = item.getShowClose();
+		String toolTipText = item.getToolTipText();
+		Font font = item.getFont();
+		Object data = item.getData();
+
+		item.dispose();
+
+		CTabItem newItem = new CTabItem(tabFolder, (showClose ? SWT.CLOSE : SWT.NONE), newIndex);
+		newItem.setText(text);
+		newItem.setImage(image);
+		newItem.setToolTipText(toolTipText);
+		newItem.setFont(font);
+		newItem.setData(data);
+		newItem.setControl(control);
+	}
+
 	@Inject
 	@Optional
 	void subscribeTopicUILabelChanged(@UIEventTopic(UIEvents.UILabel.TOPIC_ALL) Event event) {
@@ -623,6 +677,14 @@ void subscribeTopicSelectedelementChanged(
 		tabStateHandler.handleEvent(event);
 	}
 
+	@Override
+	public void removeGui(MUIElement element, Object widget) {
+		if (widget instanceof CTabFolder tabFolder && !tabFolder.isDisposed()) {
+			tabFolder.dispose();
+		}
+		element.setWidget(null);
+	}
+
 	@Override
 	protected boolean requiresFocus(MPart element) {
 		MUIElement inStack = element.getCurSharedRef() != null ? element.getCurSharedRef() : element;
@@ -1010,7 +1072,7 @@ protected void createTab(MElementContainer<MUIElement> stack, MUIElement element
 		}
 	}
 
-	private int calcIndexFor(MElementContainer<MUIElement> stack, final MUIElement part) {
+	private int calcIndexFor(MElementContainer<? extends MUIElement> stack, final MUIElement part) {
 		int index = 0;
 
 		// Find the -visible- part before this element
@@ -1036,7 +1098,7 @@ public void childRendered(final MElementContainer<MUIElement> parentElement, MUI
 		createTab(parentElement, element);
 	}
 
-	private CTabItem findItemForPart(MUIElement element, MElementContainer<MUIElement> stack) {
+	private CTabItem findItemForPart(MUIElement element, MElementContainer<? extends MUIElement> stack) {
 		if (stack == null) {
 			stack = element.getParent();
 		}