cefsharp/CefSharp · error · Exception

Unable to take screenshot while browser is loading

Error message

Unable to take screenshot while browser is loading

What it means

Thrown by the example ChromiumWebBrowserWithScreenshotSupport.TakeScreenshot when IsLoading is true. Capturing mid-navigation would yield a partial or transitional frame, so the method requires the page to be in a stable, loaded state. This is a guard sequenced after the initialization and concurrency checks.

Source

Thrown at CefSharp.Wpf.Example/Controls/ChromiumWebBrowserWithScreenshotSupport.cs:61

        {
            ScreenshotCommand = new RelayCommand(TakeScreenshot);
        }

        public Task<InteropBitmap> TakeScreenshot(Size screenshotSize, int? frameRate = 1, int? ignoreFrames = 0, CancellationToken? cancellationToken = null)
        {
            if (screenshotTaskCompletionSource != null && screenshotTaskCompletionSource.Task.Status == TaskStatus.Running)
            {
                throw new Exception("Screenshot already in progress, you must wait for the previous screenshot to complete");
            }

            if (IsBrowserInitialized == false)
            {
                throw new Exception("Browser has not yet finished initializing or is being disposed");
            }

            if (IsLoading)
            {
                throw new Exception("Unable to take screenshot while browser is loading");
            }

            var browserHost = this.GetBrowserHost();

            if (browserHost == null)
            {
                throw new Exception("IBrowserHost is null");
            }

            screenshotTaskCompletionSource = new TaskCompletionSource<InteropBitmap>(TaskCreationOptions.RunContinuationsAsynchronously);

            if (cancellationToken.HasValue)
            {
                var token = cancellationToken.Value;
                cancellationTokenRegistration = token.Register(() =>
                {
                    screenshotTaskCompletionSource.TrySetCanceled();

View on GitHub (pinned to 16bc6e0711)

Solutions

1. Wait until LoadingStateChanged reports IsLoading == false before capturing.
2. Use WaitForNavigationAsync / LoadUrlAsync and await completion, then capture.
3. Guard with `if (!browser.IsLoading)` and retry when idle.
4. For animated pages, account for the frame-rate/ignoreFrames parameters once idle.

Example fix

// before
browser.Load(url);
var shot = browser.TakeScreenshot(size); // throws: still loading

// after
await browser.LoadUrlAsync(url); // waits for load
var shot = await browser.TakeScreenshot(size);

if (!browser.IsLoading)
{
    _ = browser.TakeScreenshot(size);
}

When it happens

Trigger: Calling TakeScreenshot while a page is still loading (between LoadStart and LoadEnd/LoadingStateChanged idle); capturing immediately after Load(url) without waiting for completion.

Common situations: Screenshotting right after navigation without awaiting LoadingStateChanged; capturing during resource-heavy page loads that take seconds.

Related errors

• Screenshot already in progress, you must wait for the previo
• Browser has not yet finished initializing or is being dispos
• IBrowserHost is null
• IBrowser instance is no longer valid. Control.Handle was lik
• {nameof(viewPort)}.{nameof(viewPort.Scale)} must be greater

AI-assisted analysis of cefsharp/CefSharp@16bc6e0711 (2026-08-13). Data as JSON: /api/errors/94ce1e07cc63f289. Report an issue: GitHub.