Do not call addListener in constructors of CCombo and StyledText #2733

The method is not final, which may cause issues if a subclass overrides
it because it ends up being called upon instantiation, when the object
is not fully initialized

Since these 2 classes are not in the same package as other subclasses of
Widget, I had to resort to expanding the functionality in TypedListener.

Fixes #2733

Author: fedejeanne

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

@@ -173,7 +173,7 @@ public CCombo (Composite parent, int style) {
 	}
 
 	initAccessible();
-	addListener(SWT.ZoomChanged, this::handleDPIChange);
+	addTypedListener((ZoomChangedListener) this::handleDPIChange, SWT.ZoomChanged);
 }
 static int checkStyle (int style) {
 	int mask = SWT.BORDER | SWT.READ_ONLY | SWT.FLAT | SWT.LEFT_TO_RIGHT | SWT.RIGHT_TO_LEFT | SWT.LEAD | SWT.CENTER | SWT.TRAIL;

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

@@ -758,7 +758,7 @@ public StyledText(Composite parent, int style) {
 	initializeAccessible();
 	setData("DEFAULT_DROP_TARGET_EFFECT", new StyledTextDropTargetEffect(this));
 	if (IS_MAC) setData(STYLEDTEXT_KEY);
-	addListener(SWT.ZoomChanged, this::handleDPIChange);
+	addTypedListener((ZoomChangedListener) this::handleDPIChange, SWT.ZoomChanged);
 }
 /**
  * Adds an extended modify listener. An ExtendedModify event is sent by the

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/events/ZoomChangedListener.java

@@ -0,0 +1,34 @@
+/*******************************************************************************
+* Copyright (c) 2025 Vector Informatik GmbH and others.
+*
+* This program and the accompanying materials
+* are made available under the terms of the Eclipse Public License 2.0
+* which accompanies this distribution, and is available at
+* https://www.eclipse.org/legal/epl-2.0/
+*
+* SPDX-License-Identifier: EPL-2.0
+*
+* Contributors:
+*     Vector Informatik GmbH  - initial API and implementation
+*******************************************************************************/
+package org.eclipse.swt.events;
+
+import java.util.*;
+
+import org.eclipse.swt.*;
+import org.eclipse.swt.widgets.*;
+
+/**
+ * Interface for typed listeners that react to events of type {@code SWT.ZoomChanged}.
+ *
+ * @implNote This API is currently only implemented on Windows and GTK.
+ * SWT doesn't send zoom events events on Cocoa.
+ * </p>
+ * @see {@linkplain SWT#ZoomChanged}
+ * @since 3.132
+ *
+ */
+@FunctionalInterface
+public interface ZoomChangedListener extends EventListener {
+	void zoomChanged(Event e);
+}

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/widgets/TypedListener.java

@@ -313,6 +313,10 @@ public void handleEvent (Event e) {
 			e.doit = event.doit;
 			break;
 		}
+		case SWT.ZoomChanged: {
+			((ZoomChangedListener) eventListener).zoomChanged(e);
+			break;
+		}
 	}
 }