OffScreen - ChromeRuntime doesn't work with LoadURL

[GrabzIt]

Is there an existing issue for this?

• I have searched both open/closed issues, no issue already exists.

CefSharp Version

125.0.210

Operating System

Windows 10

Architecture

x64

.Net Version

.NET 6.0

Implementation

OffScreen

Reproduction Steps

        public static int Main(string[] args)
        {
            const string testUrl = "https://grabz.it/";

            Console.WriteLine("This example application will load {0}, take a screenshot, and save it to your desktop.", testUrl);
            Console.WriteLine("You may see Chromium debugging output, please wait...");
            Console.WriteLine();

            //Console apps don't have a SynchronizationContext, so to ensure our await calls continue on the main thread we use a super simple implementation from
            //https://devblogs.microsoft.com/pfxteam/await-synchronizationcontext-and-console-apps/
            //Continuations will happen on the main thread. Cef.Initialize/Cef.Shutdown must be called on the same Thread.
            //The Nito.AsyncEx.Context Nuget package has a more advanced implementation
            //should you wish to use a pre-build implementation.
            //https://github.com/StephenCleary/AsyncEx/blob/8a73d0467d40ca41f9f9cf827c7a35702243abb8/doc/AsyncContext.md#console-example-using-asynccontext
            //NOTE: This is only required if you use await

                var settings = new CefSettings()
                {
                    ChromeRuntime = true,
                    //By default CefSharp will use an in-memory cache, you need to specify a Cache Folder to persist data
                    CachePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache")
                };

                //Perform dependency check to make sure all relevant resources are in our output directory.
                var success = Cef.Initialize(settings, performDependencyCheck: true, browserProcessHandler: null);

                if (!success)
                {
                    throw new Exception("Unable to initialize CEF, check the log file.");
                }

                // Create the CefSharp.OffScreen.ChromiumWebBrowser instance
                using (var browser = new ChromiumWebBrowser(string.Empty))
                {
                    browser.FrameLoadEnd += Browser_FrameLoadEnd;
                    browser.LoadUrl(testUrl);
                    // Wait for user to press a key before exit
                    Thread.Sleep(20000);
                }

                // Clean up Chromium objects. You need to call this in your application otherwise
                // you will get a crash when closing.
                Cef.Shutdown();

            return 0;
        }

        private async static void Browser_FrameLoadEnd(object sender, FrameLoadEndEventArgs e)
        {
            if (e.Frame.IsValid && e.Frame.IsMain)
            {
                var bitmapAsByteArray = await ((ChromiumWebBrowser)sender).CaptureScreenshotAsync();

                // File path to save our screenshot e.g. C:\Users\{username}\Desktop\CefSharp screenshot.png
                var screenshotPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "CefSharp screenshot.png");

                Console.WriteLine();
                Console.WriteLine("Screenshot ready. Saving to {0}", screenshotPath);

                File.WriteAllBytes(screenshotPath, bitmapAsByteArray);

                Console.WriteLine("Screenshot saved. Launching your default image viewer...");

                // Tell Windows to launch the saved image.
                Process.Start(new ProcessStartInfo(screenshotPath)
                {
                    // UseShellExecute is false by default on .NET Core.
                    UseShellExecute = true
                });
                Console.WriteLine("Image viewer launched. Press any key to exit.");
            }
        }

Expected behavior

This should load the url and display a screenshot but when ChromeRuntime = true it never works. However, it does if you remove ChromeRuntime = true.

Actual behavior

It never fires the browser loaded event.

Regression?

No response

Known Workarounds

No response

Does this problem also occur in the CEF Sample Application

Yes using WPF/OffScreen command line args

Other information

No response

[Alex Maitland]

However, it does if you remove ChromeRuntime = true.

Given it works with the alloy runtime this likely needs to be fixed in CEF.

[Alex Maitland]

@GrabzIt Looking at the code in more detail, can you defer creation of the browser until after you've subscribed to the event? e.g.

// Create the CefSharp.OffScreen.ChromiumWebBrowser instance
using (var browser = new ChromiumWebBrowser(testUrl, automaticallyCreateBrowser:false))
{
  browser.FrameLoadEnd += Browser_FrameLoadEnd;
  browser.CreateBrowser();
  // Wait 
  Thread.Sleep(20000);
}

[GrabzIt]

Thanks, this approach works and seems to work with further calls to LoadURL and adding and removing the event: e.g.

              using (var browser = new ChromiumWebBrowser(testUrl, automaticallyCreateBrowser: false))
              {
                    browser.FrameLoadEnd += Browser_FrameLoadEnd;
                    browser.CreateBrowser();
                    Thread.Sleep(20000);
                    browser.FrameLoadEnd += Browser_FrameLoadEnd;
                    browser.LoadUrl("https://grabz.it/about/");
                    Thread.Sleep(20000);
              }

        private async static void Browser_FrameLoadEnd(object sender, FrameLoadEndEventArgs e)
        {
            if (e.Frame.IsValid && e.Frame.IsMain)
            {
                Console.WriteLine(e.Url);
                ((ChromiumWebBrowser)sender).FrameLoadEnd -= Browser_FrameLoadEnd;
            }
        }

Is this the way it should be used from now or are the CEF changes to the chrome runtime going to fix the issue?

[Alex Maitland]

Is this the way it should be used from now

That would be my recommendation. Pretty sure I modified most of the examples/tests a while back to use this approach. If there are any outstanding then happy to update them.

are the CEF changes to the chrome runtime going to fix the issue?

From a CefSharp point of view it probably makes sense to defer browser creation automatically if you pass in string.Empty, create the browser on the next load call.

[GrabzIt]

That sounds great thanks.