Question

I use a WebBrowser control as a “preview” for a special type of markup. I process the markup, and then set the browser’s DocumentText property to display it. This works okay.

However, sometimes the control takes upwards of 5-10 seconds for this operation to complete. Since I do this at application start up (blanking the window with DocumentText = ""), and it still takes forever to do this, I want to somehow Thread this or something so that the rest of the application can start up while the control… does whatever it does.

For reference, the function in question is:

private void btnRefresh_Click(object sender, EventArgs e) {
    try {
        scrolltop = html.Document.Body.ScrollTop;
        scrollleft = html.Document.Body.ScrollLeft;
    } catch (NullReferenceException) { }

    html.DocumentText = HtmlProcessing.ProcessCode(txtCode.Text); //takes 5-10 seconds
}

I know I can’t just fire up a thread to handle this, since I assume the WebBrowser control will puke if I try to access it from the other thread. Are there any other techniques I could use to do this?

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Edit:

Turns out, my delay was not being caused by html.DocumentText, nor by HtmlProcessing.ProcessCode, but by a bit of code that I omitted from the sample, because I thought it was irrelevant:

private void btnRefresh_Click(object sender, EventArgs e) {
    try {
        scrolltop = html.Document.Body.ScrollTop;
        scrollleft = html.Document.Body.ScrollLeft;
    } catch (NullReferenceException) { }

    html.DocumentText = HtmlProcessing.ProcessCode(txtCode.Text, GetImageList());
}

That call to GetImageList() was taking forever. The contents of the function looks like:

List<string> GetImageList() {
    List<string> ret = new List<string>();

    ret.AddRange(Directory.GetFiles(settings.LocalImageFolder).Where((f) => { return extensions.Contains(Path.GetExtension(f)); }));

    ret.AddRange(Directory.GetFiles(settings.RemoteImageFolder).Where((f) => { return extensions.Contains(Path.GetExtension(f)); }));

    return ret;
}

And, settings.RemoteImageFolder is, in fact, a network path that was taking forever. I ended up turning this into an IEnumerable<string>. That way, I only hit the network when ProcessCode actually needs files from there.

Answer 1

The problem was a slow network access that was hidden behind a property accessor, and had nothing to do with the web browser control.