gistfile1.txt

public interface IDependOnProvideContent
{
    // TODO: consider making this Task<T> instead of setting the view data directly.
    Task Content { get; set; }
}

[ProvideContent("Common/Footer")]
public class ContactDetailsController : Controller, IDependOnProvideContent
{
    Task IDependOnProvideContent.Content { get; set; }

    private Task WaitForContentAsync()
    {
        return ((IDependOnProvideContent)this).Content;
    }

    public async Task<ActionResult> Index()
    {
        await WaitForContentAsync();
        //omitted for brevity - awaits some other async methods
        return View();
    }
}

// In ProvideContentAttribute
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var controller = filterContext.Controller as IDependOnProvideContent;
    if (controller == null)
        throw new InvalidOperationException("ProvideContentAttribute controllers must derive from IDependOnProvideContent.");

    if (filterContext.Result is ViewResult)
    {
        var localPath = filterContext.RouteData.Values["controller"] + "/" + filterContext.RouteData.Values["action"];

        if (!_useControllerActionAsPath)
            localPath = _path;

        var viewResult = filterContext.Result as ViewResult;

        controller.Task = GetContentAsync(localPath, viewResult);
    }
}

private async Task GetContentAsync(string localPath, ViewResult viewResult)
{
    var content = await _contentManager.GetContent(localPath);

    if (viewResult.ViewBag.SystemContent == null)
        viewResult.ViewBag.SystemContent = new Dictionary<string, MvcHtmlString>();

    viewResult.ViewBag.SystemContent[localPath] = new DisplayContentItem(content, localPath);
}