cefsharp/CefSharp · warning · InvalidOperationException

Unexpected failure of calling CEF->GetZoomLevelAsync

Error message

Unexpected failure of calling CEF->GetZoomLevelAsync

What it means

Identical to the WPF version: after the HwndHost-based browser initializes, CefSharp calls GetZoomLevelAsync to sync the zoom level. If that task faults (browser disposed mid-call, CEF internal error), the continuation throws InvalidOperationException wrapping the original exception as InnerException.

Source

Thrown at CefSharp.Wpf/HwndHost/ChromiumWebBrowser.cs:1308

        {
            if (newValue && !IsDisposed)
            {
                var task = this.GetZoomLevelAsync();
                task.ContinueWith(previous =>
                {
                    if (previous.Status == TaskStatus.RanToCompletion)
                    {
                        UiThreadRunAsync(() =>
                        {
                            if (!IsDisposed)
                            {
                                SetCurrentValue(ZoomLevelProperty, previous.Result);
                            }
                        });
                    }
                    else
                    {
                        throw new InvalidOperationException("Unexpected failure of calling CEF->GetZoomLevelAsync", previous.Exception);
                    }
                }, TaskContinuationOptions.ExecuteSynchronously);
            }
        }

        /// <summary>
        /// The title of the web page being currently displayed.
        /// </summary>
        /// <value>The title.</value>
        /// <remarks>This property is implemented as a Dependency Property and fully supports data binding.</remarks>
        public string Title
        {
            get { return (string)GetValue(TitleProperty); }
            set { SetValue(TitleProperty, value); }
        }

        /// <summary>
        /// The title property

View on GitHub (pinned to 16bc6e0711)

Solutions

1. Subscribe to TaskScheduler.UnobservedTaskException at startup to observe and log without crashing.
2. Prevent premature disposal — ensure the HwndHost browser is not torn down during the init-completion window.
3. Inspect the InnerException (previous.Exception) to find the underlying CEF fault.
4. Upgrade CefSharp to a version with init/dispose race fixes.

Example fix

// after — observe at startup
TaskScheduler.UnobservedTaskException += (s, e) =>
{
    Log.Warn("Unobserved CEF task fault", e.Exception?.InnerException ?? e.Exception);
    e.SetObserved();
};

// No pre-call validation possible — internal library continuation.
// Observe globally:
TaskScheduler.UnobservedTaskException += (s, e) =>
{
    if (e.Exception?.Message?.Contains("GetZoomLevelAsync") == true)
    {
        Log.Warn("HwndHost CEF zoom sync faulted", e.Exception.InnerException);
        e.SetObserved();
    }
};

// Cannot catch at call site — thrown in library-internal continuation.
// Only surface: TaskScheduler.UnobservedTaskException
TaskScheduler.UnobservedTaskException += (s, e) =>
{
    e.SetObserved();
};

When it happens

Trigger: Fires inside OnIsBrowserInitializedChanged (HwndHost variant) when the GetZoomLevelAsync continuation sees a non-RanToCompletion status. The throw is in an ExecuteSynchronously continuation and surfaces as an unobserved task exception.

Common situations: HwndHost browser being disposed during or right after initialization. CEF crash during init. Race between init completion and shutdown.

Related errors

• Unexpected failure of calling CEF->GetZoomLevelAsync
• Browser has already been created. BrowserSettings must be se
• Browser has already been created. RequestContext must be set
• Cef.IsInitialized was false!.Check the log file for errors!.
• The ChromiumWebBrowser instance creates the underlying Chrom

AI-assisted analysis of cefsharp/CefSharp@16bc6e0711 (2026-08-13). Data as JSON: /api/errors/e787c93b349a7d17. Report an issue: GitHub.