Setting the background in an MVC _Layout.cshtml page - asp.net-mvc

Question

Setting every page's background is rather simple in ASP.Net WebForms where you have access to the Page_Load event in the code-behind of a MasterPage but how is this best done in MVC? After spending several hours researching various alternatives I chose to assign the value to the ViewBag through a "base" controller, derive subsequent controllers from that base and then access that value in _Layout.cshtml.
Here is the base controller, in which I assign a url that points to a specific image:
public class BaseController : Controller
{
public BaseController()
{
ViewBag.url = BingImageLoader.getBingImageUrl();
}
}
The next step is to derive subsequent controllers, in this case the HomeController from that base class:
public class HomeController : BaseController
{
public ActionResult Index()
{
return View();
}
.
.
And finally, use the ViewBag in the head element of _Layout.cshtml to set the background-image style property.
.
.
<style type="text/css">
body {
background-image: url(#ViewBag.url);
background-repeat: no-repeat;
background-size: cover;
}
</style>
</head>
This did accomplish what I set out to do; however, along the way there were a number of alternatives indicated, including using ActionFilters. To be honest, creating a CustomActionFilter and using ActionFilterAttributes and overriding OnActionExecuting seems like overkill but sometimes the simplest way is not always the best.
Ultimately, the question comes down to "Is there a better way?" Are there side-effects from introducing an intermediary? If I override my ViewBag.url in the individual controller methods, the image changes accordingly. So I have yet to find any problems but there may be other issues resulting from this approach.
So again, "Is there a better way"?

Answer 1

One possible problem I can see with this approach is if the developer forgets to subclass hist controller from BaseController.
Using a global action filter would ensure that this will never happen and the property will be always available:
public class BackgroundImageFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuted(ActionExecutedContext context)
{
context.Controller.ViewBag.url = BingImageLoader.getBingImageUrl();
}
}
which will be registered only once in your Application_Start:
protected void Application_Start()
{
...
// Register global filter
GlobalFilters.Filters.Add(new BackgroundImageFilterAttribute());
}
If you find this filter approach cumbersome as an alternative I can suggest writing a custom Html helper that could be used in your _Layout.cshtml:
<style type="text/css">
body {
background-image: url(#Html.GetBackgroundImageUrl());
background-repeat: no-repeat;
background-size: cover;
}
</style>
which might be defined as a simple extension method:
public static class HtmlExtensions
{
public static IHtmlString GetBackgroundImageUrl(this HtmlHelper html)
{
string url = BingImageLoader.getBingImageUrl();
return new HtmlString(url);
}
}