Add url parameter to css file in asp themes folder

Question

I have written a bit of code that helps with versioning of js files. Essentially it spins around the current script manager and appends the javascript file path with an md5

Answer 1

I am facing one issue that it is repeating css entry in html markup on every postback. for example, I have newabc.css. the code will change it to newabc.css?v=1. if I see html source after 5 postback, it will have 5 "newabc.css?v=1". so I added link.EnableViewState = False, it works fine but is it actually needed?

    Dim link As HtmlLink = Nothing

    For Each c As Control In Page.Header.Controls
        If TypeOf c Is HtmlLink Then
            link = TryCast(c, HtmlLink)

            If link.Href.IndexOf("App_Themes/", StringComparison.InvariantCultureIgnoreCase) >= 0 AndAlso link.Href.EndsWith(".css", StringComparison.InvariantCultureIgnoreCase) Then
                link.Href &= "?v=" & VER_CSS
                'link.EnableViewState = False
            End If
        End If
    Next

Answer 2

Avoid to invent the wheel twice by using Combres instead. Does everything you ask for, and more!

Answer 3

You can use a control adapter to neatly inject this behavior into the page as follows:

public class PageAdapter : System.Web.UI.Adapters.PageAdapter
{
    protected override void OnPreRender(System.EventArgs e)
    {
        foreach (var link in Page.Header.Controls.OfType<HtmlLink>().ToList())
            if (link.Attributes["type"].Equals("text/css", StringComparison.OrdinalIgnoreCase))
                if (link.Attributes["href"].Contains("/App_Themes/{0}/".Fill(Page.Theme), StringComparison.OrdinalIgnoreCase))
                   /* process link */

        base.OnPreRender(e);
    }
}

You can plug it in by saving the following as a *.browser file in the App_Browsers folder:

<browsers>
  <browser refID="Default">
    <controlAdapters>
      <adapter controlType="System.Web.UI.Page"
               adapterType="PageAdapter" />
    </controlAdapters>
  </browser>
</browsers>

Overall, I think Control Adapters are a powerful AOP-like mechanism for injecting behavior into control/page life-cycles; they are almost entirely ignored in favor of traditional sub-classing.