Why is my code working using a MessageBox.Show() inside the code and it doesn't work without it?

Question

I want to save the web page source code and I have the following code:

WebBrowser browser = new WebBrowser();
browser.ScriptErrorsSuppressed = true;
int SleepTime = 5000;
loadPage: browser.Navigate("https://google.com");
System.Threading.Thread.Sleep(SleepTime);
MessageBox.Show("browser.Navigae OK");
if(browser.ReadyState == WebBrowserReadyState.Complete)
{
    string path = @"htmlCode.txt";
    if(browser.Document.Body.Parent.InnerText != null)
    {
        File.WriteAllText(path, browser.Document.Body.Parent.OuterHtml, Encoding.GetEncoding(browser.Document.Encoding));
        MessageBox.Show("Success! htmlCode.txt created");
        break;
    }
    else
    {
        MessageBox.Show("browser.Document.Body.Parent.InnerText=" + browser.Document.Body.Parent.InnerText);
        MessageBox.Show("Failure htmlCode.txt not created");
    }
}

if I comment

MessageBox.Show("browser.Navigate OK");

my code it is not working... why?

https://stackoverflow.com/questions/20957182/load-url-from-txt-file-and-load-the-url-in-browser-synchronous-webclient-httpreq — Eser, May 31 '18 at 18:38
@KadarBarna Click on the link in Eser's comment. Use that answer. — 15ee8f99-57ff-4f92-890c-b56153, May 31 '18 at 18:39
@JLRishe your words fall on deaf ears, I've found it's easier to just fix it myself — Daxtron2, May 31 '18 at 18:39
https://stackoverflow.com/questions/16193084/webbrowser-control-throws-seemingly-random-nullreferenceexception — EZI, May 31 '18 at 18:45
@EdPlunkett WebBrowser is **STA** and works in the current thread context. So Thread.Sleep(anynumber) would just block the UI and WebBrowser. What makes the code work is the MessageBox... — Eser, May 31 '18 at 18:50

Steve · Answer 1 · 2018-05-31T19:03:29.547

-1

Why is it not working?

Typical Race condition

Navigation takes time to finish. Your MessageBox.Show acts like a huge delay buffer which gives web browser enough time to finish the operation.

You should be using DocumentCompleted event to ensure this does not happen.

edited May 31 '18 at 19:03

answered May 31 '18 at 18:38

Steve

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**1-** *Race condition* is commonly used when threads are involved. In OP's case, there is a single thread (UI thread). **2-** *DocumentCompleted* is the correct event. Navigated doesn't guarantee that the page is ready to use DOM objects – L.B May 31 '18 at 19:00
@L.B there is UI thread + webbrowser background thread. UI thread enters processing stage before background thread completes. I do think its considered a race condition. Updated the document completed part. – Steve May 31 '18 at 19:05
1

There is **no** *webbrowser background thread*. WB control works in UI thread. If you block the UI thread (like Thread.Sleep), WB is also blocked. – L.B May 31 '18 at 19:06

Why is my code working using a MessageBox.Show() inside the code and it doesn't work without it?

1 Answers1