ASP.NET MVC 3 Razor view returning multiple values for a Html.CheckBoxFor

Question

I have a View that contains the following Line of code:

//(DaysOfWeek is a bool[])
@Html.CheckBoxFor(m => m.Data.DaysOfWeek[0])

It starts off as false. When the user "checks" the box and returns, it returns a value for both true and false;

Here is what is being passed back as part of the form data

Data.DaysOfWeek[0]:true
Data.DaysOfWeek[0]:false

Why is it doing that?

Although @RoryMcCrossan explained the why, and a answer, I have never seen this problem, doing what you are doing. Could you post your view model, I would think bool DayOfWeek0 = Data.DaysOfWeek[0] should be either true or false if you're not using a view model, you could just do @Html.CheckBox("VariableName") and in your controller method arguments bool VariableName — Garrett Fogerlie
– Garrett Fogerlie, Commented Aug 4, 2012 at 20:37

Rory McCrossan · Accepted Answer · 2012-08-04 20:21:52Z

6

This is because standard HTML checkboxes return no value if unchecked. To make this annoying behaviour more intuitive, the CheckBoxFor method creates a checkbox and a hidden control with the same name, with a value of false, something like this:

<input type="checkbox" name="myControl" value="True" /> My control
<input type="hidden" name="myControl" value="False" />

What you will see when the form is posted is either:

False // checkbox unchecked
True,False // checkbox was checked

Therefore, to test if the box was checked you should use Contains('True'):

bool checkboxChecked = formCollection["myControl"].Contains("True");

edited Aug 4, 2012 at 20:21

answered Aug 4, 2012 at 20:14

Rory McCrossan

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1 Comment

beauXjames Over a year ago

This pestilent feature is also resolved when using binding libraries, such as knockout.js...binding directly to a Boolean occurs flawlessly. I find it best to not use RazorFor syntax in most situations, but if you still do, the checked property can be overridden with a data-bind attribute and works great.

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