Action Parameters Add a default value when No Key

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();
        }
    }
}

Brian Mains · Accepted Answer · 2010-02-15 21:07:37Z

3

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;
}

edited Feb 15, 2010 at 21:07

answered Feb 15, 2010 at 16:28

Brian Mains

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2 Comments

Jemes Over a year ago

Thanks, I've not used Action Filters that much. How can I use put the ActionParameters.ContainsKey("SectionID") check into practice?

rjlopes Over a year ago

if you want set a default value for an action param and you want to use that value on an AuthorizationFilter you can't use an ActionFilterAttribute. In that case on the AuthorizationFilter you should use the RouteData instead of the ActionParameters because the later is not available.

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