Webbrowser behaviour issues

Question

I am trying to automate Webbrowser with .NET C#. The issue is that the control or should I say IE browser behaves strange on different computers. For example, I am clickin o

Answer 1

I could recommend two things:

• Don't execute your code upon DocumentComplete event, rather do upon DOM window.onload event.
• To make sure your web page behaves in WebBrowser control the same way as it would in full Internet Explorer browser, consider implementing Feature Control.

[EDITED] There's one more suggestion, based on the structure of your code. Apparently, you perform a series of navigation/handle DocumentComplete actions. It might be more natural and easy to use async/await for this. Here's an example of doing this, with or without async/await. It illustrates how to handle onload, too:

async Task DoNavigationAsync()
{
    bool documentComplete = false;
    TaskCompletionSource<bool> onloadTcs = null;

    WebBrowserDocumentCompletedEventHandler handler = delegate 
    {
        if (documentComplete)
            return; // attach to onload only once per each Document
        documentComplete = true;

        // now subscribe to DOM onload event
        this.wb.Document.Window.AttachEventHandler("onload", delegate
        {
            // each navigation has its own TaskCompletionSource
            if (onloadTcs.Task.IsCompleted)
                return; // this should not be happening

            // signal the completion of the page loading
            onloadTcs.SetResult(true);
        });
    };

    // register DocumentCompleted handler
    this.wb.DocumentCompleted += handler;

    // Navigate to http://www.example.com?i=1
    documentComplete = false;
    onloadTcs = new TaskCompletionSource<bool>();
    this.wb.Navigate("http://www.example.com?i=1");
    await onloadTcs.Task;
    // the document has been fully loaded, you can access DOM here
    MessageBox.Show(this.wb.Document.Url.ToString());

    // Navigate to http://example.com?i=2
    // could do the click() simulation instead

    documentComplete = false;
    onloadTcs = new TaskCompletionSource<bool>(); // new task for new navigation
    this.wb.Navigate("http://example.com?i=2");
    await onloadTcs.Task;
    // the document has been fully loaded, you can access DOM here
    MessageBox.Show(this.wb.Document.Url.ToString());

    // no more navigation, de-register DocumentCompleted handler
    this.wb.DocumentCompleted -= handler;
}

Here's the same code without async/await pattern (for .NET 4.0):

Task DoNavigationAsync()
{
    // save the correct continuation context for Task.ContinueWith
    var continueContext = TaskScheduler.FromCurrentSynchronizationContext(); 

    bool documentComplete = false;
    TaskCompletionSource<bool> onloadTcs = null;

    WebBrowserDocumentCompletedEventHandler handler = delegate 
    {
        if (documentComplete)
            return; // attach to onload only once per each Document
        documentComplete = true;

        // now subscribe to DOM onload event
        this.wb.Document.Window.AttachEventHandler("onload", delegate
        {
            // each navigation has its own TaskCompletionSource
            if (onloadTcs.Task.IsCompleted)
                return; // this should not be happening

            // signal the completion of the page loading
            onloadTcs.SetResult(true);
        });
    };

    // register DocumentCompleted handler
    this.wb.DocumentCompleted += handler;

    // Navigate to http://www.example.com?i=1
    documentComplete = false;
    onloadTcs = new TaskCompletionSource<bool>();
    this.wb.Navigate("http://www.example.com?i=1");

    return onloadTcs.Task.ContinueWith(delegate 
    {
        // the document has been fully loaded, you can access DOM here
        MessageBox.Show(this.wb.Document.Url.ToString());

        // Navigate to http://example.com?i=2
        // could do the 'click()' simulation instead

        documentComplete = false;
        onloadTcs = new TaskCompletionSource<bool>(); // new task for new navigation
        this.wb.Navigate("http://example.com?i=2");

        onloadTcs.Task.ContinueWith(delegate 
        {
            // the document has been fully loaded, you can access DOM here
            MessageBox.Show(this.wb.Document.Url.ToString());

            // no more navigation, de-register DocumentCompleted handler
            this.wb.DocumentCompleted -= handler;
        }, continueContext);

    }, continueContext);
}

Note, it both cases it is still a piece of asynchronous code which returns a Task object. Here's an example of how to handle the completion of such task:

private void Form1_Load(object sender, EventArgs e)
{
    DoNavigationAsync().ContinueWith(_ => {
        MessageBox.Show("Navigation complete!");
    }, TaskScheduler.FromCurrentSynchronizationContext());
}

The benefit of using TAP pattern here is that DoNavigationAsync is a self-contained, independent method. It can be reused and it doesn't interfere with the state of parent object (in this case, the main form).