Code walkthrough

First of all, I am using Dot Net Core for this, you can easily achieve the same thing using the regular .NET Framework. Create a new class, I called mine CdnUrlHtmlHelper.cs, this makes it easy to see what it’s used for.

Within this file you will have two classes. But first, let’s have a look at the easiest part. This is reterieving the configuration setting from the configuration file.

public class CdnUrlConfig {
  private static IConfiguration _configuration;

  public CdnUrlConfig(IConfiguration configuration) {
    _configuration = configuration;
  }

  public static string CdnBaseUrl
  {
    get {
      return _configuration["CdnBaseUrl"];
    }
  }
}

Using dependency injection within Dot Net Core, I am able to access the configuration settings easily using a private property. I then pass the IConfiguration interface into the constructor of the class to set the private property. Any of my configuration settings can now be accessed using the _configuration property.

public static class CdnUrlHtmlHelper {
  public static string CdnUrl(this HtmlHelper helper, string contentPath) {
    if (contentPath.StartsWith("~")) {
      contentPath = contentPath.Substring(1);
    }

    contentPath = string.Format("{0}{1}", CdnUrlConfig.CdnBaseUrl.TrimEnd('/'), contentPath.TrimStart('/'));

    var url = new UrlHelper(new Microsoft.AspNetCore.Mvc.ActionContext(helper.ViewContext.HttpContext, helper.ViewContext.RouteData, helper.ViewContext.ActionDescriptor));

    return url.Content(contentPath);
  }
}

The next step is todefine a public static class for our actual helper. I shall move onto the usage shortly. The idea here is that I pass in the content path, then retrieve the base URL from configuration and build the URL to return back to the view engine.

I can then call this very simply, check out the examples below.

<img src="@Html.CdnUrl("~/images/image1.png")" alt="Test"/>

<link rel="stylesheet" type="text/css" href="@Html.CdnUrl("~/style/site.min.css")" />```