When using .net MVC RadioButtonFor(), how do you group so only one selection can be made?

The first parameter of Html.RadioButtonFor() should be the property name you're using, and the second parameter should be the value of that specific radio button. Then they'll have the same name attribute value and the helper will select the given radio button when/if it matches the property value.

Example:

<div class="editor-field">    <%= Html.RadioButtonFor(m => m.Gender, "M" ) %> Male    <%= Html.RadioButtonFor(m => m.Gender, "F" ) %> Female</div>

Here's a more specific example:

I made a quick MVC project named "DeleteMeQuestion" (DeleteMe prefix so I know that I can remove it later after I forget about it).

I made the following model:

namespace DeleteMeQuestion.Models{    public class QuizModel    {        public int ParentQuestionId { get; set; }        public int QuestionId { get; set; }        public string QuestionDisplayText { get; set; }        public List<Response> Responses { get; set; }        [Range(1,999, ErrorMessage = "Please choose a response.")]        public int SelectedResponse { get; set; }    }    public class Response    {        public int ResponseId { get; set; }        public int ChildQuestionId { get; set; }        public string ResponseDisplayText { get; set; }    }}

There's a simple range validator in the model, just for fun. Next up, I made the following controller:

namespace DeleteMeQuestion.Controllers{    [HandleError]    public class HomeController : Controller    {        public ActionResult Index(int? id)        {            // TODO: get question to show based on method parameter             var model = GetModel(id);            return View(model);        }        [HttpPost]        public ActionResult Index(int? id, QuizModel model)        {            if (!ModelState.IsValid)            {                var freshModel = GetModel(id);                return View(freshModel);            }            // TODO: save selected answer in database            // TODO: get next question based on selected answer (hard coded to 999 for now)            var nextQuestionId = 999;            return RedirectToAction("Index", "Home", new {id = nextQuestionId});        }        private QuizModel GetModel(int? questionId)        {            // just a stub, in lieu of a database            var model = new QuizModel            {                QuestionDisplayText = questionId.HasValue ? "And so on..." : "What is your favorite color?",                QuestionId = 1,                Responses = new List<Response>                                                {                                                    new Response                                                        {                                                            ChildQuestionId = 2,                                                            ResponseId = 1,                                                            ResponseDisplayText = "Red"                                                        },                                                    new Response                                                        {                                                            ChildQuestionId = 3,                                                            ResponseId = 2,                                                            ResponseDisplayText = "Blue"                                                        },                                                    new Response                                                        {                                                            ChildQuestionId = 4,                                                            ResponseId = 3,                                                            ResponseDisplayText = "Green"                                                        },                                                }            };            return model;        }    }}

Finally, I made the following view that makes use of the model:

<%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<DeleteMeQuestion.Models.QuizModel>" %><asp:Content ContentPlaceHolderID="TitleContent" runat="server">    Home Page</asp:Content><asp:Content ContentPlaceHolderID="MainContent" runat="server">    <% using (Html.BeginForm()) { %>        <div>            <h1><%: Model.QuestionDisplayText %></h1>            <div>            <ul>            <% foreach (var item in Model.Responses) { %>                <li>                    <%= Html.RadioButtonFor(m => m.SelectedResponse, item.ResponseId, new {id="Response" + item.ResponseId}) %>                    <label for="Response<%: item.ResponseId %>"><%: item.ResponseDisplayText %></label>                </li>            <% } %>            </ul>            <%= Html.ValidationMessageFor(m => m.SelectedResponse) %>        </div>        <input type="submit" value="Submit" />    <% } %></asp:Content>

As I understand your context, you have questions with a list of available answers. Each answer will dictate the next question. Hopefully that makes sense from my model and TODO comments.

This gives you the radio buttons with the same name attribute, but different ID attributes.

In my case, I had a collection of radio buttons that needed to be in a group.I just included a 'Selected' property in the model. Then, in the loop to output the radiobuttons just do...

@Html.RadioButtonFor(m => Model.Selected, Model.Categories[i].Title)

This way, the name is the same for all radio buttons. When the form is posted, the 'Selected' property is equal to the category title (or id or whatever) and this can be used to update the binding on the relevant radiobutton, like this...

model.Categories.Find(m => m.Title.Equals(model.Selected)).Selected = true;

May not be the best way, but it does work.

In cases where the name attribute is different it is easiest to control the radio group via JQuery. When an option is selected use JQuery to un-select the other options.