SP 2010 - Web Parts and Embedded Resources Not Working

I ran into a problem recently trying to use Embedded Resources with SharePoint 2010 web parts. I was using code I had directly used in non SharePoint ASP.Net server controls, which if you aren't familiar with, is pretty simple. I'll briefly describe how you'd use an embedded resource, then describe my problem and how I fixed it.

First, you need to just add your resource, which in my case was a stylesheet, to your project. Then, using the properties pane, set the Build Action to Embedded Resource. Once you've done that, you'll need to edit the AssemblyInfo.cs file within your project and enable the embedded resource.

[assembly: WebResource("MyAssembly.styles.MyStyleSheet.css", "text/css")]

Now you have a resource that will be embedded in your DLL. The path to that resource is specified in the WebResourceAttribute above. I usually compile and open my DLL in reflector at this point to confirm that the path I've picked is correct. Once it is, you can include your stylesheet like this:

string styleSheetUrl = Page.ClientScript.GetWebResourceUrl(this.GetType(), "MyAssembly.styles.MyStyleSheet.css");
LiteralControl styleSheetLink = new LiteralControl(string.Format("LINK SYNTAX HERE - BLOGGER WONT LET ME EMBED THE HTML", styleSheetUrl));
                Page.Header.Controls.Add(styleSheetLink);

In theory, that should work, right? It works in server controls, and it's worked for me in older web parts for MOSS 2007. But, when I built my 2010 web part, it wasn't working.

I viewed source on my page and could see that the embedded resource was added to the markup. But when I tried to load that URL myself, I got an error, implying my resource wasn't there at all! I checked and rechecked my path inside the DLL. Everything was right.

But then I noticed something different about 2010 web parts. They use a LoadControl mechanism. I was accessing my embedded resources, using the above code, directly inside the webpart.ascx.cs, not the webpart.cs file. On a hunch, I moved the code into the webpart.cs file. Success!

This got me curious, so I looked at the source for the generated HTML and noticed that the generated URL for the embedded resource had changed. Apparently, the path is based somewhat on that first parameter to GetWebResourceUrl(), which is a type. Tinkering a little more, I learned that I could actually leverage the embedded resource from the webpart.ascx.cs by making a minor adjustment.

string styleSheetUrl = Page.ClientScript.GetWebResourceUrl(this.Parent.GetType(), "MyAssembly.styles.MyStyleSheet.css");

Notice that I'm not passing the type of the parent, which for our webpart.ascx.cs, is the wrapper class that calls LoadControl.