Question

How can I set up a default value in my Action Filter when an ActionParameter is empty?

When I use the About and Area_1419 Actions on my controller the filter works fine as it picks up the passed SectionID parameter. When I use the index action I get the error below….

The given key was not present in the dictionary.
On this line…

var GetSectionID = filterContext.ActionParameters["SectionID"];

I don’t won’t to add the SectionID parameter to each controller action as it only applies to certain sections and I don’t want to add the filter to each action as the filter effects these pages aswell.

Is it possible to set up a default value for SectionID within the filter if no value is present for SectionID?

CategoriesAttribute

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace Website.ActionFilters
{
    public class CategoriesAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var GetSectionID = filterContext.ActionParameters["SectionID"];
            var NoSectionID = 1;

            if (GetSectionID == null)
            {
                filterContext.Controller.ViewData["SectionID"] = NoSectionID;
            }
            else
            {
                filterContext.Controller.ViewData["SectionID"] = GetSectionID;
            }              
        }
    }
}

Home Controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using Website.Models;
using Website.ActionFilters;

namespace Website.Controllers
{
    [HandleError,Categories]
    public class HomeController : Controller
   {
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult About(int SectionID)
        {
            return View();
        }

        public ActionResult Area_1419(int SectionID)
        {
            return View();
        }
    }
}

Answer 1

ActionParameters is a dictionary; check for the key via ActionParameters.ContainsKey(“SectionID”) first. With a dictionary, checking for a key never returns null, but throws that exception because it always expects the key.

if (filterContext.ActionParameters.ContainsKey("SectionID"))
{
   //Code to process as section ID
   filterContext.Controller.ViewData["SectionID"] = filterContext.ActionParameters["SectionID"]; 
}
else
{
   //Code to process as if no section ID
   filterContext.Controller.ViewData["SectionID"] = 1;
}