Implement Cross-Platform Dark Theme Preferred API in SWT

Author: vogella

bundles/org.eclipse.swt/Eclipse SWT/cocoa/org/eclipse/swt/widgets/Display.java

@@ -1774,6 +1774,20 @@ public static boolean isSystemDarkTheme () {
 	return OS.isSystemDarkAppearance();
 }
 
+/**
+ * Informs the operating system that the application prefers a dark
+ * theme for native components such as title bars, scrollbars, and
+ * native dialogs.
+ *
+ * @param preferred true if the dark theme is preferred, false otherwise.
+ *
+ * @since 3.134
+ */
+public void setDarkThemePreferred(boolean preferred) {
+	checkDevice();
+	OS.setTheme(preferred);
+}
+
 int getLastEventTime () {
 	NSEvent event = application != null ? application.currentEvent() : null;
 	if (event == null) return 0;

bundles/org.eclipse.swt/Eclipse SWT/cocoa/org/eclipse/swt/widgets/Shell.java

@@ -2063,6 +2063,26 @@ void setScrolling () {
 	view.performSelector(OS.sel_clearDeferFlushing, null, 0.0, display.runLoopModes());
 }
 
+/**
+ * Informs the operating system that the application prefers a dark
+ * theme for native components such as title bars, scrollbars, and
+ * native dialogs.
+ *
+ * @param preferred true if the dark theme is preferred, false otherwise.
+ *
+ * @since 3.134
+ */
+public void setDarkThemePreferred(boolean preferred) {
+	checkWidget();
+	if (OS.VERSION < OS.VERSION (10, 14, 0)) return;
+	if (window == null) return;
+	String appearanceName = preferred ? "NSAppearanceNameDarkAqua" : "NSAppearanceNameAqua";
+	NSAppearance appearance = NSAppearance.appearanceNamed (NSString.stringWith (appearanceName));
+	if (appearance != null) {
+		OS.objc_msgSend(window.id, OS.sel_setAppearance_, appearance.id);
+	}
+}
+
 @Override
 public void setText (String string) {
 	checkWidget();

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Display.java

@@ -2619,6 +2619,20 @@ public static boolean isSystemDarkTheme () {
 	return themeDark;
 }
 
+/**
+ * Informs the operating system that the application prefers a dark
+ * theme for native components such as title bars, scrollbars, and
+ * native dialogs.
+ *
+ * @param preferred true if the dark theme is preferred, false otherwise.
+ *
+ * @since 3.134
+ */
+public void setDarkThemePreferred(boolean preferred) {
+	checkDevice();
+	OS.setTheme(preferred);
+}
+
 int getLastEventTime () {
 	return lastEventTime;
 }

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Shell.java

@@ -2879,6 +2879,20 @@ static Region mirrorRegion (Region region) {
 void setRelations() {
 }
 
+/**
+ * Informs the operating system that the application prefers a dark
+ * theme for native components such as title bars, scrollbars, and
+ * native dialogs.
+ *
+ * @param preferred true if the dark theme is preferred, false otherwise.
+ *
+ * @since 3.134
+ */
+public void setDarkThemePreferred(boolean preferred) {
+	checkWidget();
+	display.setDarkThemePreferred(preferred);
+}
+
 @Override
 public void setText (String string) {
 	super.setText (string);

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Display.java

@@ -2179,6 +2179,20 @@ public static boolean isSystemDarkTheme () {
 	return isDarkTheme;
 }
 
+/**
+ * Informs the operating system that the application prefers a dark
+ * theme for native components such as title bars, scrollbars, and
+ * native dialogs.
+ *
+ * @param preferred true if the dark theme is preferred, false otherwise.
+ *
+ * @since 3.134
+ */
+public void setDarkThemePreferred(boolean preferred) {
+	checkDevice();
+	OS.setTheme(preferred);
+}
+
 int getLastEventTime () {
 	return OS.GetMessageTime ();
 }

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Shell.java

@@ -576,7 +576,7 @@ void createBalloonTipHandle () {
 	OS.SetWindowLongPtr (balloonTipHandle, OS.GWLP_WNDPROC, display.windowProc);
 }
 
-void setTitleColoring() {
+void setTitleColoring(boolean preferred) {
 	int attributeID = 0;
 	if (OsVersion.IS_WIN10_2004) {
 		// Documented since build 20348, but was already present since build 19041
@@ -590,10 +590,24 @@ void setTitleColoring() {
 		return;
 	}
 
-	int[] value = new int[] {1};
+	int[] value = new int[] {preferred ? 1 : 0};
 	OS.DwmSetWindowAttribute (handle, attributeID, value, 4);
 }
 
+/**
+ * Informs the operating system that the application prefers a dark
+ * theme for native components such as title bars, scrollbars, and
+ * native dialogs.
+ *
+ * @param preferred true if the dark theme is preferred, false otherwise.
+ *
+ * @since 3.134
+ */
+public void setDarkThemePreferred(boolean preferred) {
+	checkWidget();
+	setTitleColoring(preferred);
+}
+
 @Override
 void createHandle () {
 	boolean embedded = handle != 0 && (state & FOREIGN_HANDLE) == 0;
@@ -627,7 +641,7 @@ void createHandle () {
 
 	if (!embedded) {
 		if (display.useShellTitleColoring) {
-			setTitleColoring();
+			setTitleColoring(true);
 		}
 
 		int bits = OS.GetWindowLong (handle, OS.GWL_STYLE);

examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet393.java

@@ -0,0 +1,57 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Eclipse Foundation 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:
+ *     Eclipse Foundation - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.snippets;
+
+import org.eclipse.swt.*;
+import org.eclipse.swt.layout.*;
+import org.eclipse.swt.widgets.*;
+
+/**
+ * Dark Theme Preferred API snippet: demonstrate how to request a dark theme for 
+ * native components (title bars, scrollbars, and native dialogs).
+ *
+ * For a list of all SWT example snippets see
+ * http://www.eclipse.org/swt/snippets/
+ */
+public class Snippet393 {
+
+public static void main (String [] args) {
+	Display display = new Display ();
+	
+	/* Signal that the application prefers a dark theme */
+	display.setDarkThemePreferred(true);
+	
+	Shell shell = new Shell (display);
+	shell.setText("Snippet 393 - Dark Theme Preferred");
+	shell.setLayout(new GridLayout(1, false));
+	
+	Label label = new Label(shell, SWT.NONE);
+	label.setText("The title bar and native dialogs should appear dark if supported by the OS.");
+	
+	Button button = new Button(shell, SWT.PUSH);
+	button.setText("Open DirectoryDialog");
+	button.addListener(SWT.Selection, event -> {
+		DirectoryDialog dialog = new DirectoryDialog(shell);
+		dialog.setMessage("Select a directory (dialog should be dark)");
+		dialog.open();
+	});
+	
+	shell.pack ();
+	shell.open ();
+	while (!shell.isDisposed ()) {
+		if (!display.readAndDispatch ()) display.sleep ();
+	}
+	display.dispose ();
+}
+}