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Posted 8 Feb 2006

WebResource ASP.NET 2.0 explained

, 26 Feb 2006
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WebResource (rumours and lies exposed): this is how you really do it.


This code drop is part of Redux series. This article started out to be about a dropdown date/time ASP.NET 2.0 server control. So I built the control and all its ancillary JavaScript, along with the images, and then everything was put into a zip file for uploading to the CodeProject. The installation instructions for the control went something like this:

  • Unzip the contents to a folder.
  • Copy the DLL to the Bin folder of your new project.
  • Copy the JavaScript file.
  • Copy the CSS file.
  • Copy the images.

Hey, wait a minute, this is really lame, why all the extra files, why not embed them into the DLL as resources. That was the beginning of three days of hell trying to understand and work with WebResources. I have boiled it down to about twenty lines of working code.

Nothing else on the net gives you an actual working sample and a lot of the information is simply wrong (possibly because it was based on beta versions). Well, this code compiles and runs on the release version of .NET 2.0.

Code snippets

Create a project which looks like this (you can get the control from the download and then just add an ASP.NET project to the solution):

Highlight the three files in MyResources, and in the Properties window, set Build Action to Embedded Resource:

The source for the control is as follows:

namespace MyWebResourceProj
  [ToolboxData("<{0}:MyWebResource runat="server"></{0}:MyWebResource>")]
  public class MyWebResource : System.Web.UI.WebControls.TextBox
      protected override void RenderContents(HtmlTextWriter output)

      protected override void OnInit(EventArgs e)
           this.GetType(), "Test", 

        // create the style sheet control
        // and put it in the document header
        string csslink = "<link href='" + 
           + "' rel='stylesheet' type='text/css' />";
        LiteralControl include = new LiteralControl(csslink);

This is not a discussion on server controls, so let's focus on the parameters of GetWebResourceUrl:

  • this.GetType() - mandatory, just do it.
  • "MyWebResourceProj.MyResources.Test.js" - this is the most misunderstood parameter and the source of just about all errors. It is composed of [Assembly of this project].[Folder containing resource].[Filename of resource].

No matter what you read anywhere else, including Microsoft's official documentation (which is wrong), if you don't do it this way, you will fail (I know this from personal experience).

Now on to the AssemblyInfo.cs:

[assembly: System.Web.UI.WebResource(
      "MyWebResourceProj.MyResources.Test.css", "text/css")]
[assembly: System.Web.UI.WebResource(
      "text/javascript", PerformSubstitution = true)]
[assembly: System.Web.UI.WebResource(
      "MyWebResourceProj.MyResources.Test.gif", "image/gif")]

You need to specify the resource name exactly as you did in your program code. You need to specify the mime-type. If the file contains JavaScript, you may want to have ASP.NET perform text substitution. For example, you may have a line in JavaScript like:

document.write("<img src='Test.gif'>");

When you embed your images in a resource, you no longer know the name of it as it appears in the resource. To fix this, code as follows:

document.write("<img src='<%=WebResource("MyWebResourceProj" + 

All the "official documentation" and all the articles on the web say that you can leave [AssemblyName].[FolderName] out. But they are dead wrong!

Note: if you are using this control as the base class of another, see yc4king's note below.


KonstantinG has pointed out an error which only becomes apparent when your namespace is not the same as your assembly name. Previously, I had indicated that the name of the resource is: [Namespace of this project].[Folder containing resource].[Filename of resource], but really it is [Assembly of this project].[Folder containing resource].[Filename of resource]. As always, the best way to find information on this is by using Lutz Roeder's .NET Reflector available at

SmashGrab / Redux series

I have recently started two series of articles here at CodeProject.

Smash and Grab is intended as a series of short articles on one specific code technique. Redux is intended as a series of longer articles which attempts to reduce a complicated topic (like WebResource) into its basic constituent parts and show that once you have all the information, it isn't really that hard. To find the Smash and Grab articles, search for the keyword SmashGrab. To find the Redux articles, search for the keyword Redux. I welcome any contributions to either series, but please follow the guidelines when submitting articles to either.


So there you have it, everything you need to know to use WebResources. This article documented how to place CSS files in the <head> section, extract JavaScript files, dynamically change the contents of a JavaScript file.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Gary Dryden
Software Developer (Senior)
Canada Canada
No Biography provided

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Comments and Discussions

GeneralThanks!!!! Pin
maurocodeproject22-Jan-07 13:50
membermaurocodeproject22-Jan-07 13:50 
GeneralMy Toolbox image not reflecting with new image Pin
Ramesh Tamma16-Jan-07 8:33
memberRamesh Tamma16-Jan-07 8:33 
GeneralDLL Resource Reference Pin
TonyCsr15-Nov-06 9:53
memberTonyCsr15-Nov-06 9:53 
GeneralThe folder problem Pin
ennixo14-Sep-06 11:16
memberennixo14-Sep-06 11:16 
QuestionBut Atlas Changes everything? Pin
jokva13-Sep-06 10:00
memberjokva13-Sep-06 10:00 
GeneralPage.ClientScript does not compile Pin
webber12345610-Sep-06 8:49
memberwebber12345610-Sep-06 8:49 
Generalthis.GetType() - mandatory, just do it. - EXPLAINED Pin
Adam Selene7-Sep-06 15:40
memberAdam Selene7-Sep-06 15:40 
GeneralRe: this.GetType() - mandatory, just do it. - EXPLAINED Pin
steph7530-Nov-06 9:30
membersteph7530-Nov-06 9:30 
Actually, the type used as a parameter doesn't need to extend Control. It can be an empty class. As long as the class is located within the same assembly as the resource, it should work.
General[Assembly of this project].[Folder containing resource].[Filename of resource] Pin
mephix4-Sep-06 6:08
membermephix4-Sep-06 6:08 
GeneralRe: [Assembly of this project].[Folder containing resource].[Filename of resource] Pin
stmarti22-Jan-07 6:01
memberstmarti22-Jan-07 6:01 
GeneralRe: [Assembly of this project].[Folder containing resource].[Filename of resource] Pin
cueshot4-Jun-07 10:31
membercueshot4-Jun-07 10:31 
GeneralRe: [Assembly of this project].[Folder containing resource].[Filename of resource] Pin
cueshot14-Jun-07 14:44
membercueshot14-Jun-07 14:44 
GeneralCheck that embedded resource exist before call Pin
Michael Freidgeim1-Sep-06 18:25
memberMichael Freidgeim1-Sep-06 18:25 
GeneralRe: Check that embedded resource exist before call Pin
stmarti22-Jan-07 6:25
memberstmarti22-Jan-07 6:25 
GeneralEmbedding an aspx Pin
Andrew de Klerk24-Aug-06 0:14
memberAndrew de Klerk24-Aug-06 0:14 
GeneralRe: Embedding an aspx Pin
Adam Selene7-Sep-06 15:47
memberAdam Selene7-Sep-06 15:47 
GeneralRe: Embedding an aspx Pin
Andrew de Klerk7-Sep-06 22:02
memberAndrew de Klerk7-Sep-06 22:02 
AnswerRe: Embedding an aspx Pin
Talk To The Hand6-Apr-07 22:06
memberTalk To The Hand6-Apr-07 22:06 
GeneralWrite out variabel or text in Embedded resource Pin
Skoder12-Aug-06 6:55
memberSkoder12-Aug-06 6:55 
QuestionBrowser Caching??? Pin
paul.tyng21-Jul-06 9:42
memberpaul.tyng21-Jul-06 9:42 
AnswerRe: Browser Caching??? Pin
Adam Selene7-Sep-06 16:00
memberAdam Selene7-Sep-06 16:00 
JokeSmall note Pin
Artur M.22-May-06 3:04
memberArtur M.22-May-06 3:04 
QuestionRe: Small note Pin
oujima6714-Jul-06 15:13
memberoujima6714-Jul-06 15:13 
GeneralRe: Small note Pin
Adam Selene7-Sep-06 16:03
memberAdam Selene7-Sep-06 16:03 
AnswerRe: Small note Pin
gedw9922-Mar-07 11:49
membergedw9922-Mar-07 11:49 

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