cefsharp/CefSharp · error · Exception

{GetType().Name}.{memberName} can no longer be modified, set

Error message

{GetType().Name}.{memberName} can no longer be modified, settings must be changed before the underlying browser has been created.

What it means

Thrown by FreezableBase.ThrowIfFrozen when a property/method of a freezable settings object (e.g. JavascriptBindingSettings, or JavascriptObjectRepository) is modified after Freeze() was called. CefSharp freezes settings once the underlying browser/context is created so that configuration cannot change mid-lifecycle; the message identifies the offending type.member (via CallerMemberName). The exception uses a base Exception with a composite message.

Source

Thrown at CefSharp/Internals/FreezableBase.cs:25

namespace CefSharp.Internals
{
    /// <summary>
    /// Base classes for Feezable settings objects
    /// </summary>
    public class FreezableBase
    {
        private bool frozen;

        public void Freeze()
        {
            frozen = true;
        }

        protected void ThrowIfFrozen([System.Runtime.CompilerServices.CallerMemberName] string memberName = "")
        {
            if (frozen)
            {
                throw new Exception(GetType().Name + "." + memberName + " can no longer be modified, settings must be changed before the underlying browser has been created.");
            }
        }
    }
}

View on GitHub (pinned to 16bc6e0711)

Solutions

1. Configure all FreezableBase settings before creating the browser/repository that consumes them.
2. Do not mutate JavascriptBindingSettings properties after the browser is created; create a new settings instance for a new browser.
3. Register all JS objects up front, since JavascriptObjectRepository.Register freezes the repository.
4. If you must change config, recreate the browser/repository with new settings rather than mutating a frozen one.

Example fix

// before (mutates after browser creation)
var settings = new JavascriptBindingSettings();
var browser = new ChromiumWebBrowser(url);
// ... later ...
settings.JavascriptBindingApiEnabled = false; // throws

// after (configure first)
var settings = new JavascriptBindingSettings { JavascriptBindingApiEnabled = false };
var browser = new ChromiumWebBrowser(url);

// FreezableBase has no public IsFrozen; track in your own lifecycle:
if (!browserCreated)
{
    settings.AlwaysInterceptAsynchronously = true;
}

try
{
    settings.JavascriptBindingApiEnabled = value;
}
catch (Exception ex) when (ex.Message.Contains("can no longer be modified"))
{
    // Settings were frozen at browser creation; recreate the browser with new settings instead.
}

When it happens

Trigger: Setting a property (e.g. JavascriptBindingApiEnabled, AlwaysInterceptAsynchronously) on JavascriptBindingSettings after it was frozen, or calling JavascriptObjectRepository.Register through a path that re-triggers a frozen setter. Freeze() is invoked when the browser/repository is bound/initialized.

Common situations: Changing JS binding settings at runtime after the browser is created; reconfiguring a repository that already had an object registered (Register calls Freeze internally); late initialization that touches settings after Cef.Initialize or browser creation; sharing a settings instance across browsers and mutating it for the second one.

Related errors

• IBrowser
• Unable to invoke ExecuteDevToolsMethod on CEF UI Thread.
• settings
• Cef.Shutdown has already been called, it's no longer possibl
• converter

AI-assisted analysis of cefsharp/CefSharp@16bc6e0711 (2026-08-13). Data as JSON: /api/errors/9fb3175fd939bcd7. Report an issue: GitHub.