How to set ViewBag properties for all Views without using a base class for Controllers?

Question

In the past I've stuck common properties, such as the current user, onto ViewData/ViewBag in a global fashion by having all Controllers inherit from a common base controller.

This allowed my to use IoC on the base controller and not just reach out into global shared for such data.

I'm wondering if there is an alternate way of inserting this kind of code into the MVC pipeline?

Answer 1

The best way is using the ActionFilterAttribute. I'll show you how to use it in .Net Core and .Net Framework.

.Net Core 2.1 & 3.1

public class ViewBagActionFilter : ActionFilterAttribute
{
    public override void OnResultExecuting(ResultExecutingContext context)
    {
        // for razor pages
        if (context.Controller is PageModel)
        {
            var controller = context.Controller as PageModel;
            controller.ViewData.Add("Avatar", $"~/avatar/empty.png");
            // or
            controller.ViewBag.Avatar = $"~/avatar/empty.png";

            //also you have access to the httpcontext & route in controller.HttpContext & controller.RouteData
        }

        // for Razor Views
        if (context.Controller is Controller)
        {
            var controller = context.Controller as Controller;
            controller.ViewData.Add("Avatar", $"~/avatar/empty.png");
            // or
            controller.ViewBag.Avatar = $"~/avatar/empty.png";

            //also you have access to the httpcontext & route in controller.HttpContext & controller.RouteData
        }

        base.OnResultExecuting(context);
    }
}

Then you need to register this in your startup.cs.

.Net Core 3.1

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews(options => { options.Filters.Add(new Components.ViewBagActionFilter()); });
}

.Net Core 2.1

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(options =>
        {
            options.Filters.Add(new Configs.ViewBagActionFilter());
        });
}

Then you can use it in all views and pages

@ViewData["Avatar"]
@ViewBag.Avatar

---

.Net Framework (ASP.NET MVC .Net Framework)

public class UserProfilePictureActionFilter : ActionFilterAttribute
{

    public override void OnResultExecuting(ResultExecutingContext filterContext)
    {
        filterContext.Controller.ViewBag.IsAuthenticated = MembershipService.IsAuthenticated;
        filterContext.Controller.ViewBag.IsAdmin = MembershipService.IsAdmin;

        var userProfile = MembershipService.GetCurrentUserProfile();
        if (userProfile != null)
        {
            filterContext.Controller.ViewBag.Avatar = userProfile.Picture;
        }
    }

}

register your custom class in the global. asax (Application_Start)

protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        GlobalFilters.Filters.Add(new UserProfilePictureActionFilter(), 0);

    }

Then you can use it in all views

@ViewBag.IsAdmin
@ViewBag.IsAuthenticated
@ViewBag.Avatar

---

Also there is another way

Creating an extension method on HtmlHelper

[Extension()]
public string MyTest(System.Web.Mvc.HtmlHelper htmlHelper)
{
    return "This is a test";
}

Then you can use it in all views

@Html.MyTest()