CODEWITHSUNDEEP
asp.net-mvc
Frank Krueger
Frank Krueger

Reputation: 70993

Why does ASP.NET MVC Html.CheckBox output two INPUTs with the same name?

Why in the world does the line:

<%= Html.CheckBox("ForSale", Model.Product.ForSale)%> For Sale

result in the following HTML:

<input id="ForSale" name="ForSale" type="checkbox" value="true" />
<input name="ForSale" type="hidden" value="false" />
For Sale

Now whenever I check the box and access Request.Form["ForSale"], I get the ridiculous answer of "true,false". Am I supposed to parse that?

This hidden field doesn't appear for the other HtmlHelper controls, so why does it for CheckBox?

How do I turn this stupid "feature" off? Or did the HtmlHelper just outgrow its usefulness?

Update

From the answer below, it seems that there is some logic behind this. I have prepared a little extension method so I don't have to think about it (thanks to @eu-ge-ne):

    public static bool GetCheckBoxValue(this System.Web.HttpRequestBase req, 
                                        string name) {
        return Convert.ToBoolean(req.Form.GetValues(name).First());
    }

Upvotes: 32

Views: 15723

Answers (7)

Stef Heyenrath
Stef Heyenrath

Reputation: 9830

I took a different approach:

Do not use the Html.CheckBoxFor or Html.CheckBox helper method to render a checkbox, but render it using normal html:

<input id="ShowOther" name="ShowOther" value="<%=Model.ShowOther %>" type="checkbox" <% if (Model.ShowOther)  { %>checked="checked"<% } %> />

And I've added a jQuery script which sets the value when the checkbox is checked/unchecked.

<script type="text/javascript">
    $(function() {
        $('#ShowOther').click(function() {
            var checked = $(this).attr('checked');
            if (checked != undefined)
                $(this).val(true);
            else
                $(this).val(false);
        });
    });
</script>

As far as I could test this, it seems that the correct value is always sent to the Controller, and no more issues with "true,false".

Upvotes: 6

Pierre Henri Kuate
Pierre Henri Kuate

Reputation: 1

I think the cleanest solution is to do:

(bool)formCollection["key"].ConvertTo(typeof(bool))

Upvotes: 0

Doga
Doga

Reputation: 281

try

request.form["chkBoxes"].replace("false","").split(new char[] {','}, stringsplitoptions.removeemptyentries);

Upvotes: 0

eu-ge-ne
eu-ge-ne

Reputation: 28153

Now whenever I check the box and access Request.Form["ForSale"], I get the ridiculous answer of "true,false". Am I supposed to parse that?

Try this:

var ForSale = Convert.ToBoolean(Request.Form.GetValues("ForSale").First());

UPDATED:

What if in the next MVC build it will return the value in the revers order "false, true"? ... – Mastermind

var ForSale = Request.Form.GetValues("ForSale")
    .Select(x => x.ToUpperInvariant()).Contains("TRUE");

// or

// FormatException can be thrown from Convert.ToBoolean()
var ForSale = Request.Form.GetValues("ForSale")
    .Select(x => Convert.ToBoolean(x)).Contains(true);

Upvotes: 2

Brad Gignac
Brad Gignac

Reputation: 819

Here's how I've done it in one of my apps. Frustrating, but it seems to work.

public virtual ActionResult Edit(int id, FormCollection values)
{
    SomeObject dbData = _repository.GetSomeObject(id);

    try
    {
        UpdateModel(dbData);
        if (values.GetValues("CheckBoxId").Contains("true")) 
            dbData.SomeBooleanProperty = true;
        else 
            dbData.SomeBooleanProperty = false;

        _repository.Save();

        Session["Success"] = "Successfully edited the part.";
        return RedirectToAction("Index");
    }
    catch
    {
        // Handle validation errors here
        return View(new SomeObjectFormViewModel(dbData));
    }
}

Hope this helps. If you've got any follow-up questions, just leave a comment and I'll update my answer accordingly.

Upvotes: 3

CoderDennis
CoderDennis

Reputation: 13837

If a CheckBox is not checked, then it will not be included in the form submission. So this "feature" gives you a result for every CheckBox. Those that are not checked will be simply "false".

I have implemented my own CheckBox helper functions that work differently. Most of the time I don't want just true or false, but just a collection of the values of the checked boxes. It's great for selecting certain items by their id on which to perform an action. I don't want the unchecked items even in the list.

You can take a look at the source code for the html extensions and use a similar structure to create your own CheckBox methods.

http://aspnet.codeplex.com/sourcecontrol/changeset/view/23011?projectName=aspnet#288010

I would post mine, but I'm not using the standard HtmlHelper class, so it would probably be more confusing. I did add a value parameter to my CheckBox functions so that I can use a specific id value instead of "true" or "false".

Upvotes: 2

blowdart
blowdart

Reputation: 56500

It forces the field to be included if it's unchecked. If you uncheck a check box it doesn't get sent as part of the page - they are only sent if they're checked, and then there's a value of true. The hidden field ensures that false will be send if the check box is unchecked, as the hidden field is always sent.

Upvotes: 41

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