Cefsharp initializing for the second time throws error

Question

My application needs to invoke (off screen) browser on request and cleanup once it is done.

So I created an offscreen browser

 public class OffScreenBrowser 
{
    private static ChromiumWebBrowser _browser;

    private static CefSettings _settings;

    public void Load(string url,System.Drawing.Size size)
    {
        if (Cef.IsInitialized) return;
        Init(new BrowserProcessHandler());

        _browser = new ChromiumWebBrowser(url) {Size = size};
        _browser.NewScreenshot += _browser_NewScreenshot;
    }
    public System.Windows.Controls.Image BrowserImage { get; set; }
    public Action NewScreenShotAction { get; set; }

    private void _browser_NewScreenshot(object sender, EventArgs e)
    {
        var bitmap = _browser.ScreenshotOrNull();
        Application.Current.Dispatcher.Invoke(new Action(() =>
        {
            using (MemoryStream memory = new MemoryStream())
            {
                bitmap.Save(memory, ImageFormat.Png);
                memory.Position = 0;
                BitmapImage bitmapImage = new BitmapImage();
                bitmapImage.BeginInit();
                bitmapImage.StreamSource = memory;
                bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
                bitmapImage.EndInit();

                BrowserImage = new System.Windows.Controls.Image() {Source = bitmapImage};
                NewScreenShotAction();
            }
        }));
    }

    public void Close()
    {
        _browser.NewScreenshot -= _browser_NewScreenshot;
        _browser.Dispose();
        _settings.Dispose();
        Cef.Shutdown();
    }

    public static void Init(IBrowserProcessHandler browserProcessHandler)
    {
        _settings = new CefSettings();
        if (!Cef.Initialize(_settings, true, browserProcessHandler))
            throw new Exception("Unable to Initialize Cef");
    }
}

The idea is-on clicking a button create browser and on clicking another button close the browser

private OffScreenBrowser offScreenBrowser;

private void OPen_OnClick(object sender, RoutedEventArgs e)
{
    var address = @"https://www.google.co.uk";
    var width = 200;
    var height = 100;
    var windowSize = new System.Drawing.Size(width, height);
     offScreenBrowser = new OffScreenBrowser();
    offScreenBrowser.Load(address, windowSize);

    offScreenBrowser.NewScreenShotAction = () => 
    {
        Browser.Content = offScreenBrowser.BrowserImage;
    };
}

private void Close_OnClick(object sender, RoutedEventArgs e)
{
    offScreenBrowser.Close();
}

On the first click it all works fine. On clicking close it seems like the cleanup is fine.

But when I click the open button for the second time I am getting an exception as below

"An unhandled exception of type 'System.AccessViolationException' occurred in CefSharp.Core.dll

Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

What am I doing wrong?

Answer 1

This is a limitation in Chromium framework.

CEF can only be Initialized/Shutdown once per process, See Need to Know/Limitations for more details, this is a limitation of the underlying Chromium framework.

Answer 2

In my case I had a similar situation. But for me, I just needed the same app to have multiple instances so that it can be runned in different screens at the same time.

The solution I found is really simple; you just need to change the "RootCachePath" on CefSettings. The reason for this is that the cache path of each instance cannot be the same.

Finally, I delete the folder created for this purpose when the app is closed.

Here an example:

    Program.rootPath = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile) + Program.rootPath + DateTime.Now.Ticks;
    
    CefSettings settings = new CefSettings();
    settings.IgnoreCertificateErrors = true;
    settings.RootCachePath = Program.rootPath;
    Cef.Initialize(settings);

    browser = new ChromiumWebBrowser(url);