how to override a views Layout declaration

Question

In asp.net MVC 3 is there a way to override the Layout declaration set in a view from a controller or action filter?

@{
    Layout = "~/Views/Shared/_Layout.cshtml";
}

I have tried overriding the MasterName property in the OnResultExecuted or the OnResultExecuting like the following code snippet, to no avail.

public override void OnResultExecuting(ResultExecutingContext filterContext)
{
    var view = filterContext.Result as ViewResult;
    view.MasterName = null;
}

Answer 1

You can create an action filter to override Layout file, but if you want to remove it, you will have to create an empty layout file instead of assigning the Master property to null. Like this:

public class OverrideLayoutFilter : ActionFilterAttribute
{
    public override void OnResultExecuting(ResultExecutingContext filterContext)
    {
        var view = filterContext.Result as ViewResult;
        view.MasterName = "_LayoutEmpty";
        base.OnResultExecuting(filterContext);
    }
}

Controller:

public class HomeController : Controller
{
    [OverrideLayoutFilter]
    public ActionResult Index()
    {
        return View();
    }
}

Now your new layout file needs to be placed in SharedFolder and you only put the RenderBody function inside

_LayoutEmpty.cshtml

@RenderBody()

Note: If you have sections defined in a view that you want to override layout you will also have to define those sections with an empty content.

Answer 2

Another place where you can control the layout is in the _ViewStart.cshtml.

Here, you can do the logic you need and programatically specify which layout to use. This allows you to place the logic in only one place and keep it out of the view.

@{
    if(myBusinessRule)
    {
       Layout = "~/Views/Shared/_Layout.cshtml";
    }
    else
    {
       Layout = "~/Views/Shared/_SecondaryLayout.cshtml";
    }
}

Blog post where it was introduced by Scott Gu