– How to handle checkboxes in ASP.NET MVC forms

Caution: This question is over nine years old!

Your best option is to search for newer questions, or to search the answers below looking for your specific version of MVC, as many answers here are obsolete now.

If you do find an answer that works for your version, please make sure the answer contains the version of MVC you are using.
(The original question starts below)

This seems a bit bizarre to me, but as far as I can tell, this is how you do it.

I have a collection of objects, and I want users to select one or more of them. This says to me "form with checkboxes." My objects don't have any concept of "selected" (they're rudimentary POCO's formed by deserializing a wcf call). So, I do the following:

public class SampleObject{
  public Guid Id {get;set;}
  public string Name {get;set;}

In the view:

    using (Html.BeginForm())
  <%foreach (var o in ViewData.Model) {%>
    <%=Html.CheckBox(o.Id)%>&nbsp;<%= o.Name %>
  <input type="submit" value="Submit" />

And, in the controller, this is the only way I can see to figure out what objects the user checked:

public ActionResult ThisLooksWeird(FormCollection result)
  var winnars = from x in result.AllKeys
          where result[x] != "false"
          select x;
  // yadda

Its freaky in the first place, and secondly, for those items the user checked, the FormCollection lists its value as "true false" rather than just true.

Obviously, I'm missing something. I think this is built with the idea in mind that the objects in the collection that are acted upon within the html form are updated using UpdateModel() or through a ModelBinder.

But my objects aren't set up for this; does that mean that this is the only way? Is there another way to do it?

Best Solution

Html.CheckBox is doing something weird - if you view source on the resulting page, you'll see there's an <input type="hidden" /> being generated alongside each checkbox, which explains the "true false" values you're seeing for each form element.

Try this, which definitely works on ASP.NET MVC Beta because I've just tried it.

Put this in the view instead of using Html.CheckBox():

<% using (Html.BeginForm("ShowData", "Home")) {  %>
  <% foreach (var o in ViewData.Model) { %>
    <input type="checkbox" name="selectedObjects" value="<%=o.Id%>">
    <%= o.Name %>
  <input type="submit" value="Submit" />

Your checkboxes are all called selectedObjects, and the value of each checkbox is the GUID of the corresponding object.

Then post to the following controller action (or something similar that does something useful instead of Response.Write())

public ActionResult ShowData(Guid[] selectedObjects) {
    foreach (Guid guid in selectedObjects) {
    return (new EmptyResult());

This example will just write the GUIDs of the boxes you checked; ASP.NET MVC maps the GUID values of the selected checkboxes into the Guid[] selectedObjects parameter for you, and even parses the strings from the Request.Form collection into instantied GUID objects, which I think is rather nice.