Question

I am venturing into WPF – first time in (VB).NET – and trying to re-create a project I started in MS Access VBA. It basically scrapes a series of pages within a web application. As you may have surmised I am having trouble with the LoadCompleted event.

I have searched and found some information on it, but the “flow” of the code only lends itself to waiting for one page to load. For example:

http://social.msdn.microsoft.com/Forums/nn-NO/wpf/thread/52c1bc55-dd41-468c-8759-a42726635d4b

All of the code execution is run in the DocumentLoaded event which works fine when you just need to navigate to one page and execute code. But I need to perform a series of these cycles for my application.

How can I reliably wait for the document to fully load while still keeping the code execution in the same Sub AND not locking the UI thread?

Here’s a basic idea of what I’m trying to do.

1. Navigate to page
2. Wait for page to fully load
3. do stuff
4. Navigate to page
5. Rinse, Repeat

P.S – .NET is very new to me so please don’t give my brain a stack overflow 😉

Thanks,
Brian

-## EDIT ##-

This is what I use to do in VBA. This is exactly what I’m trying to do, just in the “.NET” way and without blocking the UI Thread:

Dim oIE = New SHDocVw.InternetExplorer

        With oIE
            .Navigate(strURL)
            .Visible = False


           ' loop until the page finishes loading
           Do While oIE.Busy : Loop
           Do While oIE.ReadyState <> 4 : Loop

           'Code goes here to read DOM, get fields and click a button (logging in to site)
           'My code execution is done and now I'm ready to go to the next page and read the DOM

           .Navigate(strURL)

        End With

.
.
.
.

That’s it. Repeat for n times. my interactions with each DOM are significantly different.

Answer 1

I would just call Navigate again at the end of the LoadCompleted handler. Then, I guess, use a window-scoped variable to keep track of your target URLs.

List<string> _urls;
int _i = 0;
private void Window_Loaded(object sender, RoutedEventArgs e)
{
    _urls = new List<string>() { url1, url2, url3 };    // URLs to navigate
    webBrowser1.LoadCompleted += webBrowser1_LoadCompleted;
    webBrowser1.Navigate(_urls[_i]);
}
void webBrowser1_LoadCompleted(object sender, NavigationEventArgs e)
{
    // do stuff

    i++;
    var nextUrl = _urls[i];
    webBrowser1.Navigate(nextUrl);
}

EDIT

Maybe something like this would be more suitable. After each cycle, you can set up the next URL as well as its handler.

class NavIteration
{
    public string Url { get; set; }
    public delegate void HandleResult(object sender, NavigationEventArgs e);
    public HandleResult ResultHandler { get; set; }
}

NavIteration CurrentIteration;

void setNextIteration()
{
    CurrentIteration = null;
    CurrentIteration = new NavIteration() { 
        Url = someurl, 
        ResultHandler = (sender, e) => {
            // handle
        }
    };
}

private void Window_Loaded(object sender, RoutedEventArgs e)
{
    webBrowser1.LoadCompleted += webBrowser1_LoadCompleted;
    setNextIteration();
    webBrowser1.Navigate();
}

void webBrowser1_LoadCompleted(object sender, NavigationEventArgs e)
{
    CurrentIteration.ResultHandler(sender, e);
    setNextIteration();
    webBrowser1.Navigate(CurrentIteration.Url);
}