Asp.net MVC 3 global querystring?

Question

I'm building a generic web application for two business groups. The logo/banner needs to be changed based on the querystring. For example, if the url is http://foo.com/test?bg=a it shows the logo for business group a and if the url is http://foo.com/test?bg=b it shows the logo for business group b. This is not a problem if I only had one action. But I have many actions.

I could check the query string on all actions but there must be a nice way to do it. I have an perception that I need to do something with the routing stuff but just don't know how. Can anyone please let me know how to do it?

Answer 1

You can write a Custom Routing Handler and use routing to extract the querystring as a parameter, and pass into RouteData where it can be accessed anywhere.

public class RouteWithQueryStringValueHandler : MvcRouteHandler
{
    private readonly string key;

    public RouteWithQueryStringValueHandler(string key)
        : base()
    {
        this.key = key;
    }

    protected override IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        var request = requestContext.HttpContext.Request;
        var qsValue = requestContext.HttpContext.Request[key];
        var router = base.GetHttpHandler(requestContext);
        requestContext.RouteData.DataTokens[key] = qsValue;
        return router;
    }
}

Register as follows:

routes.Add(new Route("{controller}/{action}/{id}", 
                 new RouteValueDictionary(
                         new { controller = "Home", 
                               action = "Index",
                               id = UrlParameter.Optional 
                         }),
                 new RouteWithQueryStringValueHandler("bg")));

Get the logo for Routing data:

var logo = RouteData.DataTokens["bg"];

Answer 2

You could write a custom helper method which based on the query string parameter will append a given class name to some div. Then of course you would have different class definitions in your CSS file applying a background-image.

For example:

public static class HtmlExtensions
{
    public static string BannerClass(this HtmlHelper html)
    {
        var bg = html.ViewContext.Controller.ValueProvider.GetValue("bg");
        if (bg == null || string.IsNullOrEmpty(bg.AttemptedValue))
        {
            // no bg parameter => return a default class
            return "default_banner";
        }

        if (string.Equals("a", bg.AttemptedValue))
        {
            return "banner_a";
        }
        else if (string.Equals("b", bg.AttemptedValue))
        {
            return "banner_b";
        }

        // unknown value for the bg parameter => return a default class
        return "default_banner";
    }
}

and then in your _Layout you could apply this class to some placeholder like a div or even the body:

<div class="@Html.BannerClass()">OK</div>

This way it will always be applied for all view in your application.

Now all that's left is to define your CSS rules for the different banners:

.default_banner {
    background-image: url('../images/default_banner.png')
}

.banner_a {
    background-image: url('../images/banner_a.png')
}

.banner_b {
    background-image: url('../images/banner_b.png')
}