MVC Value Providers - Cookie Value Providers

Asp.NET MVC - Value providers

What are value providers?

A Value provider is a class that ties into the request pipeline and gets values out for you,

now this is fine for simple requests like when someone submits a form on your site. 

The built in one is quite powerful and covers simple data types all the way to creating models for you.

But what if you require a value that's not part of the form data or the query string, for example a header or a cookie.

Then you'll need to find or write a custom value provider to get one of these values in your action.

So today we're going to build a Cookie Value provider

public class HttpCookieValueProvider : System.Web.Mvc.IValueProvider
    {
        private ControllerContext _context;

        public HttpCookieValueProvider ( ControllerContext context )
        {
            if ( context == null )
                throw new ArgumentNullException( "context" );

            this._context = context;
        }

        #region IValueProvider Members

        bool IValueProvider.ContainsPrefix ( string prefix )
        {
            return prefix.StartsWith( "C_", true, CultureInfo.CurrentCulture );
        }

        ValueProviderResult IValueProvider.GetValue ( string key )
        {
            if ( string.IsNullOrWhiteSpace( key ) ) return null;

            string[] segments = key.Remove( 0, 1 ).Split( new char[] { '_' }, StringSplitOptions.RemoveEmptyEntries );

            if ( segments.Length == 0 )
                return null;

            HttpCookie cookie = this._context.HttpContext.Request.Cookies[segments[0]];

            if ( cookie == null )
                return null;

            if ( segments.Length < 2 )
                return new ValueProviderResult( cookie.Value, cookie.Value, CultureInfo.CurrentCulture );

            return new ValueProviderResult( cookie.Values.GetValues( segments[1] ), cookie.Values[segments[1]], CultureInfo.CurrentCulture );
        }

        #endregion
    }

Which basically Implements IValueProvider which can be found in the Mvc and Web Api namespaces. This Value provider above intends to get a value from a Request Cookie.

It checks your Mvc Action method for a parameter starting with C_ in this case then looks for a cookie with the name following C_(Name of the cookie here) 

Taking it a step further if you have a Cookie with more than one value use 
C_(Name of the cookie)_(Name of the value within the cookie you'd like to get)

Next hook to hook it up to MVC

We'll need a factory which will create a new instance of our Value Provider using the Controller Context

 public class HttpCookieValueProviderFactory : ValueProviderFactory
    {
        public override IValueProvider GetValueProvider ( ControllerContext controllerContext )
        {
            return new HttpCookieValueProvider( controllerContext );
        }

    }

Lastly

In the Global.asax file inside the Application_Start() method, register

//Cookie Value Provider Custom
ValueProviderFactories.Factories.Add( new HttpCookieValueProviderFactory() );

And thats it you're done. Now you can just pull cookie values out of your action methods like

public ActionResult (string C_City){
}