WebBrowser control does not instantiate a document

Question

I have a WebBrowser control in my Windows Forms app but it just doesn't load the document.

Here is my code:

webBrowser1.Navigate(@"C:\Pages\myLocalWebPage.html");
File.WriteAllText(path,webBrowser1.Document.Body.Parent.OuterHtml, Encoding.GetEncoding(webBrowser1.Document.Encoding));

And it gives me a null reference exception on the second line. I guess that the Document is not instantiated at all.

Answer 1

You try to access a document that is not loaded yet, since you access the Document property just after you navigate to the a new Uri, and it's why you get a NullReferenceException.

You need to use the WebBrowser.DocumentCompleted event.

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When does that event get fired ?

From MSDN, the WebBrowser control navigates to a new document whenever one of the following properties is set or methods is called: Url, DocumentText, DocumentStream, Navigate, GoBack, GoForward, GoHome, GoSearch.

The navigation will trigger the following events in this order:

• Navigating event:

  Handle the Navigating event to receive notification before navigation begins. Handling this event lets you cancel navigation if certain conditions have not been met, for example, when the user has not completely filled out a form.

• Navigated event:

  Handle the Navigated event to receive notification when the WebBrowser control finishes navigation and has begun loading the document at the new location.

• DocumentCompleted event:

  Handle the DocumentCompleted event to receive notification when the new document finishes loading. When the DocumentCompleted event occurs, the new document is fully loaded, which means you can access its contents through the Document, DocumentText, or DocumentStream property.

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I have the control invisible.It is not supposed to be used by the user.I am just trying to load a document from the code-behind

The fact the control is not visible shouldn't be a problem. I have tested with a webbrowser created at runtime that I have not added to a form (see sample below), and the event is still raised.

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How does it get activated?

Here is a possible implementation:

private WebBrowser wb;

private void Button1_Click(System.Object sender, System.EventArgs e)
{
    if (wb == null) {
        wb = new WebBrowser();
        wb.DocumentCompleted += wb_DocumentCompleted;
    }
    wb.Navigate("YourPath");
}

private void wb_DocumentCompleted(object sender, System.Windows.Forms.WebBrowserDocumentCompletedEventArgs e)
{
    IO.File.WriteAllText(IO.Path.Combine(Application.StartupPath, "Test.html"), wb.Document.Body.Parent.OuterHtml, System.Text.Encoding.GetEncoding(wb.Document.Encoding));
}

See also this thread Can I wait for a webbrowser to finish navigating, using a for loop?

Answer 2

Your local file path needs to be referenced similar to this (the file:// is key):

Uri uri = new Uri("file://C:/Pages/myLocalWebPage.html");
webBrowser1.Navigate(uri);