How can I use Url.Action with list parameters?

Question

Say I have an action method:

[HttpGet]
public ActionResult Search(List<int> category){
    ...
}

The way the MVC model binding works, it expects a list of category like this:

/search?category=1&category=2

So my questions are:

How do I create that link using Url.Action() if I just hardcode it?

Url.Action("Search", new {category=???}) //Expect: /search?category=1&category=2

How do I create that link using Url.Action() if my input is a list of int?

var categories = new List<int>(){1,2}; //Expect: /search?category=1&category=2

Url.Action("Search", new {category=categories}) //does not work,

http://stackoverflow.com/questions/12285372/how-to-pass-a-filtered-list-into-action-parameters-asp-net-mvc — markpsmith
– markpsmith, Commented Feb 14, 2014 at 17:22

Sam B · Accepted Answer · 2014-02-14 17:41:20Z

20

Instead of using an Anonymous Type, build a RouteValueDictionary. Format the parameters as parameter[index].

@{
    var categories = new List<int>() { 6, 7 };

    var parameters = new RouteValueDictionary();

    for (int i = 0; i < categories.Count; ++i)
    {
        parameters.Add("category[" + i + "]", categories[i]);
    }
}

Then,

@Url.Action("Test", parameters)

answered Feb 14, 2014 at 17:41

Sam B

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4 Comments

Max Toro Over a year ago

It works, but it's not HTML form compatible, and adds unnecessary complexity to the querystring.

Kjensen Over a year ago

I can confirm this works. @MaxToro: Can you elaborate on those two statements?

Max Toro Over a year ago

@Kjensen e.g. you have a checkbox list to select categories, the default HTML behavior is to send category=val1&category=val2 and not category[1]=val1&category[2]=val2, unless you name the checkboxes like that, and that's the unnecessary complexity.

Meena Over a year ago

the baove solution is not working for me, can you please help me out

Max Toro · Accepted Answer · 2014-02-14 18:26:55Z

Build the querystring yourself, it's evident that UrlHelper was not designed for this use case.

Using:

   static class QueryStringBuilder {

      public static string ToQueryString(this NameValueCollection qs) {
         return ToQueryString(qs, includeDelimiter: false);
      }

      public static string ToQueryString(this NameValueCollection qs, bool includeDelimiter) {

         var sb = new StringBuilder();

         for (int i = 0; i < qs.AllKeys.Length; i++) {

            string key = qs.AllKeys[i];
            string[] values = qs.GetValues(key);

            if (values != null) {
               for (int j = 0; j < values.Length; j++) {

                  if (sb.Length > 0)
                     sb.Append('&');

                  sb.Append(HttpUtility.UrlEncode(key))
                     .Append('=')
                     .Append(HttpUtility.UrlEncode(values[j]));
               }
            }
         }

         if (includeDelimiter && sb.Length > 0)
            sb.Insert(0, '?');

         return sb.ToString();
      }
   }

You can write this:

var parameters = new NameValueCollection {
  { "category", "1" },
  { "category", "2" }
};

var url = Url.Action("Search") + parameters.ToQueryString(includeDelimiter: true);

Siddarth Modi · Accepted Answer · 2020-04-04 17:19:20Z

Instead Type Casting to “object” or “object[]” or using RouteValueDictionary. A simple way to achieve the same is using “Newtonsoft.Json”

If using .Net Core 3.0 or later;

Default to using the built in System.Text.Json parser implementation.

@using System.Text.Json;

…….

@Url.Action(“ActionName”, “ControllerName”, new {object = JsonConvert.SerializeObject(‘@ModalObject’)  }))

If stuck using .Net Core 2.2 or earlier;

Default to using Newtonsoft JSON.Net as your first choice JSON Parser.

@using Newtonsoft.Json;

…..

@Url.Action(“ActionName”, “ControllerName”, new {object = JsonConvert.SerializeObject(‘@ModalObject’)  }))

you may need to install the package first.

PM> Install-Package Newtonsoft.Json

Then,

public ActionResult ActionName(string modalObjectJSON)
{
    Modal modalObj = new Modal();
    modalObj = JsonConvert.DeserializeObject<Modal>(modalObjectJSON);

}

Slobodonosor · Accepted Answer · 2014-02-14 18:13:43Z

-2

It´s not the best way but you can Join the category list with your QueryString parameter name.

@Url.Action("Search", new {category = string.Join("&category=", categories)});

answered Feb 14, 2014 at 18:13

Slobodonosor

624 bronze badges

1 Comment

tkburbidge Over a year ago

This does not work because the '&' and '=' are url encoded. The end result looks like: /Search?category=category1%26category%3Dcategory2 rather than: /Search?category=category1&category=category2

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