CTabFolder should allow to listen on tab count changes

- added CTabFolder2Listener.itemsCount(CTabFolderEvent) API
- added CTabFolder2Listener.itemsCountAdapter(Consumer<CTabFolderEvent>)
API
- updated CTabFolder to notify CTabFolder2Listener on creating/removing
items
- added unit test
- bumped minor version segment for new API added

Fixes #620

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CTabFolder.java

@@ -744,6 +744,15 @@ Image createButtonImage(Display display, int button) {
 	image = new Image(display, new AutoScaleImageDataProvider(display, imageData, DPIUtil.getDeviceZoom()));
 	return image;
 }
+
+private void notifyItemCountChange() {
+	CTabFolderEvent e = new CTabFolderEvent(this);
+	e.widget = CTabFolder.this;
+	for (CTabFolder2Listener listener : folderListeners) {
+		listener.itemsCount(e);
+	}
+}
+
 void createItem (CTabItem item, int index) {
 	if (0 > index || index > getItemCount ())SWT.error (SWT.ERROR_INVALID_RANGE);
 	item.parent = this;
@@ -769,6 +778,7 @@ void createItem (CTabItem item, int index) {
 	} else {
 		updateFolder(REDRAW_TABS);
 	}
+	notifyItemCountChange();
 }
 void destroyItem (CTabItem item) {
 	if (inDispose) return;
@@ -789,6 +799,7 @@ void destroyItem (CTabItem item) {
 		updateButtons();
 		setButtonBounds();
 		redraw();
+		notifyItemCountChange();
 		return;
 	}
 
@@ -820,6 +831,7 @@ void destroyItem (CTabItem item) {
 
 	requestLayout();
 	updateFolder(UPDATE_TAB_HEIGHT | REDRAW_TABS);
+	notifyItemCountChange();
 }
 
 /**

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CTabFolder2Listener.java

@@ -115,6 +115,34 @@ public interface CTabFolder2Listener extends SWTEventListener {
  */
 public void showList(CTabFolderEvent event);
 
+/**
+ * Sent when the tab items count changes
+ * 
+ * @param event from observed tab folder
+ * @since 3.124
+ */
+public default void itemsCount(CTabFolderEvent event) {
+	// do nothing by default
+}
+
+/**
+ * Static helper method to create a <code>CTabFolder2Listener</code> for the
+ * {@link #itemsCount(CTabFolderEvent e)}) method, given a lambda expression or
+ * a method reference.
+ *
+ * @param c the consumer of the event
+ * @return CTabFolder2Listener
+ * @since 3.124
+ */
+public static CTabFolder2Listener itemsCountAdapter(Consumer<CTabFolderEvent> c) {
+	return new CTabFolder2Adapter() {
+		@Override
+		public void itemsCount(CTabFolderEvent e) {
+			c.accept(e);
+		}
+	};
+}
+
 /**
  * Static helper method to create a <code>CTabFolder2Listener</code> for the
  * {@link #close(CTabFolderEvent e)}) method, given a lambda expression or a method reference.

bundles/org.eclipse.swt/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-Name: %pluginName
 Bundle-Vendor: %providerName
 Bundle-SymbolicName: org.eclipse.swt; singleton:=true
-Bundle-Version: 3.123.100.qualifier
+Bundle-Version: 3.124.0.qualifier
 Bundle-ManifestVersion: 2
 Bundle-Localization: plugin
 DynamicImport-Package: org.eclipse.swt.accessibility2

bundles/org.eclipse.swt/pom.xml

@@ -21,7 +21,7 @@
     </parent>
     <groupId>org.eclipse.swt</groupId>
     <artifactId>org.eclipse.swt</artifactId>
-    <version>3.123.100-SNAPSHOT</version>
+    <version>3.124.0-SNAPSHOT</version>
     <packaging>eclipse-plugin</packaging>
 
     <properties>

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_CTabFolder.java

@@ -25,10 +25,14 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.BiConsumer;
+import java.util.function.Consumer;
 
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
+import org.eclipse.swt.custom.CTabFolder2Listener;
+import org.eclipse.swt.custom.CTabFolderEvent;
 import org.eclipse.swt.custom.CTabItem;
 import org.eclipse.swt.custom.SashForm;
 import org.eclipse.swt.graphics.Color;
@@ -143,6 +147,48 @@ private void createTabFolder(List<String> events, int numItems) {
 	ctabFolder.setSelection(ctabFolder.getItem(0));
 }
 
+@Test
+public void test_ItemCountListsners() {
+	int expectedTabsCount = 1;
+	int expectedEventsCount = 0;
+	createTabFolder(null, expectedTabsCount);
+	AtomicLong itemCount = new AtomicLong();
+	AtomicLong callCount = new AtomicLong();
+	Consumer<CTabFolderEvent> tabCountUpdate = e -> {
+		itemCount.set(ctabFolder.getItemCount());
+		callCount.incrementAndGet();
+	};
+	ctabFolder.addCTabFolder2Listener(CTabFolder2Listener.itemsCountAdapter(tabCountUpdate));
+
+	CTabItem item1 = new CTabItem(ctabFolder, SWT.NONE);
+	expectedTabsCount ++;
+	expectedEventsCount++;
+	assertEquals(expectedTabsCount, ctabFolder.getItemCount());
+	assertEquals(ctabFolder.getItemCount(), itemCount.get());
+	assertEquals(expectedEventsCount, callCount.get());
+
+	CTabItem item2 = new CTabItem(ctabFolder, SWT.NONE);
+	expectedEventsCount++;
+	expectedTabsCount ++;
+	assertEquals(expectedTabsCount, ctabFolder.getItemCount());
+	assertEquals(ctabFolder.getItemCount(), itemCount.get());
+	assertEquals(expectedEventsCount, callCount.get());
+
+	item1.dispose();
+	expectedEventsCount++;
+	expectedTabsCount --;
+	assertEquals(expectedTabsCount, ctabFolder.getItemCount());
+	assertEquals(ctabFolder.getItemCount(), itemCount.get());
+	assertEquals(expectedEventsCount, callCount.get());
+
+	item2.dispose();
+	expectedEventsCount++;
+	expectedTabsCount --;
+	assertEquals(expectedTabsCount, ctabFolder.getItemCount());
+	assertEquals(ctabFolder.getItemCount(), itemCount.get());
+	assertEquals(expectedEventsCount, callCount.get());
+}
+
 @Test
 public void test_consistency_KeySelection() {
 	List<String> events = new ArrayList<>();