How to open a a-3 pdf file using chromium web browser using C# .NET

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Hi, I need help to open an a/3 pdf file in the Chromium web browser using C#.

I tried some samples but I got some errors. Please help using the sample code.

What I have tried:

C#

using ChromiumWebBrowser = CefSharp.WinForms.ChromiumWebBrowser;
using CefSettings = CefSharp.WinForms.CefSettings;

namespace CefTest
{
    public class Program
    {
        private static ChromiumWebBrowser browser;

        [STAThread]
        public static async Task Main(string[] args)
        {
            await HtmlToPdfHeadless();
        }

        private static async Task HtmlToPdfHeadless()
        {
            const string testUrl = "https://www.google.com/";
            var settings = new CefSettings();
            Cef.Initialize(settings);
            browser = new ChromiumWebBrowser(testUrl);
            string path = "Test.pdf";
            Task<bool> printToPdfAsync = PrintToPdfAsync(path);
            var result = await printToPdfAsync;
        }
            
        public static async Task<bool> PrintToPdfAsync(string path)
        {
            return await browser.PrintToPdfAsync(path);

        }
    }


}

Posted 27-Dec-23 19:27pm

runtime_terror

Updated 8-Jan-24 18:19pm

v2

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Comments

Richard MacCutchan 28-Dec-23 4:28am

Please show the exact error messages in your question, and indicate where they occur.

runtime_terror 8-Jan-24 4:12am

System.Exception: 'IBrowser instance is null. Browser has likely not finished initializing or is in the process of disposing.'

Error occurring in this line:--> await HtmlToPdfHeadless();

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Pete O'Hanlon · Answer 1 · 2024-01-09T00:11:00

The issue that you are hitting is that you instantiate the web browser, and immediately attempt to call PrintToPdf. At this point, the browser is still loading. The browser exposes an [^]IsBrowserInitializedChanged event that is fired when the browser is initialized. A word of caution - this event is raised on a CEF thread, so you may need to dispatch back to the main thread if you are using this in a screen based application.

Note, as you are attempting to print the current page to a PDF, you need to wait for the page to finish loading. You need to handle this event LoadingStateChanged Event[^] which is fired twice, the first time when the page starts loading, and then a second time when the page load completes. There is every possibility that the load page could fail, so you need to validate that it has completed successfully before you actually attempt to print the page out.