Core - Add AddPreferenceObserver support.

CefSharp.Core.Runtime.RefAssembly/CefSharp.Core.Runtime.netcore.cs

@@ -1,4 +1,4 @@
-//------------------------------------------------------------------------------
+//------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by a tool.
 //     GenAPI Version: 5.0.2.37403
@@ -291,6 +291,7 @@ protected virtual void Dispose(bool A_0) { }
         public virtual System.Threading.Tasks.Task<CefSharp.ResolveCallbackResult> ResolveHostAsync(System.Uri origin) { throw null; }
         public virtual void SetContentSetting(string requestingUrl, string topLevelUrl, CefSharp.Enums.ContentSettingTypes contentType, CefSharp.Enums.ContentSettingValues value) { }
         public virtual bool SetPreference(string name, object value, out string error) { throw null; }
+        public virtual CefSharp.IRegistration AddPreferenceObserver(string name, CefSharp.Callback.IPreferenceObserver observer) { throw null; }
         public virtual void SetWebsiteSetting(string requestingUrl, string topLevelUrl, CefSharp.Enums.ContentSettingTypes contentType, object value) { }
         public virtual CefSharp.IRequestContext UnWrap() { throw null; }
     }

CefSharp.Core.Runtime/CefSharp.Core.Runtime.netcore.vcxproj

@@ -418,6 +418,7 @@
     <ClInclude Include="Internals\CefRequestContextHandlerAdapter.h" />
     <ClInclude Include="PostData.h" />
     <ClInclude Include="PostDataElement.h" />
+    <ClInclude Include="Internals\PreferenceObserverAdapter.h" />
     <ClInclude Include="Request.h" />
     <ClInclude Include="resource.h" />
     <ClInclude Include="UrlRequest.h" />

CefSharp.Core.Runtime/CefSharp.Core.Runtime.netcore.vcxproj.filters

@@ -325,6 +325,9 @@
     <ClInclude Include="Internals\CefTaskDelegate.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="Internals\PreferenceObserverAdapter.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="Internals\CefFrameWrapper.h">

CefSharp.Core.Runtime/CefSharp.Core.Runtime.vcxproj

@@ -317,6 +317,7 @@
     <ClInclude Include="Internals\CefRequestContextHandlerAdapter.h" />
     <ClInclude Include="PostData.h" />
     <ClInclude Include="PostDataElement.h" />
+    <ClInclude Include="Internals\PreferenceObserverAdapter.h" />
     <ClInclude Include="Request.h" />
     <ClInclude Include="resource.h" />
     <ClInclude Include="UrlRequest.h" />

CefSharp.Core.Runtime/CefSharp.Core.Runtime.vcxproj.filters

@@ -319,6 +319,9 @@
     <ClInclude Include="Internals\CefTaskDelegate.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="Internals\PreferenceObserverAdapter.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="Internals\CefPermissionPromptCallbackWrapper.h">
       <Filter>Header Files</Filter>
     </ClInclude>

CefSharp.Core.Runtime/Internals/PreferenceObserverAdapter.h

@@ -0,0 +1,41 @@
+// Copyright © 2026 The CefSharp Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+
+#include "include/cef_preference.h"
+#include <gcroot.h>
+
+#include "StringUtils.h"
+
+using namespace CefSharp::Callback;
+
+namespace CefSharp
+{
+    namespace Internals
+    {
+        private class PreferenceObserverAdapter : public CefPreferenceObserver
+        {
+        private:
+            gcroot<IPreferenceObserver^> _handler;
+
+        public:
+            PreferenceObserverAdapter(IPreferenceObserver^ handler)
+            {
+                _handler = handler;
+            }
+
+            ~PreferenceObserverAdapter()
+            {
+                delete _handler;
+                _handler = nullptr;
+            }
+
+            virtual void OnPreferenceChanged(const CefString& name) override
+            {
+                _handler->OnPreferenceChanged(StringUtils::ToClr(name));
+            }
+
+            IMPLEMENT_REFCOUNTINGM(PreferenceObserverAdapter);
+        };
+    }
+}

CefSharp.Core.Runtime/RequestContext.cpp

@@ -11,9 +11,12 @@
 #include "Internals\CefSchemeHandlerFactoryAdapter.h"
 #include "Internals\CefCompletionCallbackAdapter.h"
 #include "Internals\CefResolveCallbackAdapter.h"
+#include "Internals\PreferenceObserverAdapter.h"
 #include "Internals\TypeConversion.h"
+#include "Internals\CefRegistrationWrapper.h"
 
 using namespace System::Runtime::InteropServices;
+using namespace CefSharp::Callback;
 
 namespace CefSharp
 {
@@ -117,6 +120,17 @@ namespace CefSharp
             return success;
         }
 
+        IRegistration^ RequestContext::AddPreferenceObserver(String^ name, IPreferenceObserver^ observer)
+        {
+            ThrowIfDisposed();
+
+            ThrowIfExecutedOnNonCefUiThread();
+
+            auto registration = _requestContext->AddPreferenceObserver(StringUtils::ToNative(name), new PreferenceObserverAdapter(observer));
+
+            return gcnew CefRegistrationWrapper(registration);
+        }
+
         void RequestContext::ClearCertificateExceptions(ICompletionCallback^ callback)
         {
             ThrowIfDisposed();

CefSharp.Core.Runtime/RequestContext.h

@@ -16,6 +16,7 @@
 
 using namespace System::Runtime::InteropServices;
 using namespace System::Threading::Tasks;
+using namespace CefSharp::Callback;
 
 namespace CefSharp
 {
@@ -254,6 +255,23 @@ namespace CefSharp
             /// application thread will be the CEF UI thread.</remarks>
             virtual bool CanSetPreference(String^ name);
 
+            /// <summary>
+            /// Add an observer for preference changes. <paramref name="name"/> is the name of the
+            /// preference to observe. If <paramref name="name"/> is empty then all preferences will
+            /// be observed. Observing all preferences has performance consequences and
+            /// is not recommended outside of testing scenarios. The observer will remain
+            /// registered until the returned Registration object is destroyed. This
+            /// method must be called on the browser process UI thread.
+            /// </summary>
+            /// <param name="name">preference key</param>
+            /// <param name="observer">preference observer</param>
+            /// <remarks>Use Cef.UIThreadTaskFactory to execute this method if required,
+            /// <see cref="IBrowserProcessHandler.OnContextInitialized"/> and ChromiumWebBrowser.IsBrowserInitializedChanged are both
+            /// executed on the CEF UI thread, so can be called directly.
+            /// When CefSettings.MultiThreadedMessageLoop == false (the default is true) then the main
+            /// application thread will be the CEF UI thread.</remarks>
+            virtual IRegistration^ AddPreferenceObserver(String^ name, IPreferenceObserver^ observer);
+
             /// <summary>
             /// Set the value associated with preference name. If value is null the
             /// preference will be restored to its default value. If setting the preference

CefSharp.Core/RequestContext.cs

@@ -7,6 +7,7 @@
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using CefSharp.Callback;
 using CefSharp.Enums;
 
 namespace CefSharp
@@ -174,6 +175,12 @@ public bool SetPreference(string name, object value, out string error)
             return requestContext.SetPreference(name, value, out error);
         }
 
+        /// <inheritdoc/>
+        public IRegistration AddPreferenceObserver(string name, IPreferenceObserver observer)
+        {
+            return requestContext.AddPreferenceObserver(name, observer);
+        }
+
         /// <inheritdoc/>
         public void ClearCertificateExceptions(ICompletionCallback callback)
         {

CefSharp/Callback/IPreferenceObserver.cs

@@ -0,0 +1,23 @@
+// Copyright © 2026 The CefSharp Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+
+using System;
+
+namespace CefSharp.Callback
+{
+    /// <summary>
+    /// Implemented by the client to observe preference changes and registered via
+    /// <see cref="IRequestContext.AddPreferenceObserver"/>. The methods of this class will
+    /// be called on the browser process UI thread.
+    /// </summary>
+    public interface IPreferenceObserver : IDisposable
+    {
+        /// <summary>
+        /// Called when a preference has changed. The new value can be retrieved using
+        /// <see cref="IRequestContext.GetPreference"/>.
+        /// </summary>
+        /// <param name="name">preference key</param>
+        void OnPreferenceChanged(string name);
+    }
+}

CefSharp/IRequestContext.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using CefSharp.Callback;
 using CefSharp.Enums;
 
 namespace CefSharp
@@ -158,6 +159,23 @@ public interface IRequestContext : IDisposable
         /// application thread will be the CEF UI thread.</remarks>
         bool SetPreference(string name, object value, out string error);
 
+        /// <summary>
+        /// Add an observer for preference changes. <paramref name="name"/> is the name of the
+        /// preference to observe. If <paramref name="name"/> is empty then all preferences will
+        /// be observed. Observing all preferences has performance consequences and
+        /// is not recommended outside of testing scenarios. The observer will remain
+        /// registered until the returned Registration object is destroyed. This
+        /// method must be called on the browser process UI thread.
+        /// </summary>
+        /// <param name="name">preference key</param>
+        /// <param name="observer">preference observer</param>
+        /// <remarks>Use Cef.UIThreadTaskFactory to execute this method if required,
+        /// <see cref="IBrowserProcessHandler.OnContextInitialized"/> and ChromiumWebBrowser.IsBrowserInitializedChanged are both
+        /// executed on the CEF UI thread, so can be called directly.
+        /// When CefSettings.MultiThreadedMessageLoop == false (the default is true) then the main
+        /// application thread will be the CEF UI thread.</remarks>
+        IRegistration AddPreferenceObserver(string name, IPreferenceObserver observer);
+
         /// <summary>
         /// Clears all certificate exceptions that were added as part of handling
         /// <see cref="IRequestHandler.OnCertificateError"/>. If you call this it is