CheckBox helper keeps sending false value no matter what's the selection - asp.net-mvc

Question

Here's my code:
#using (Html.BeginForm("AddMCondition", "Admin"))
{
<td class="admin-textbox">
#Html.TextBox("txtMCondition")
</td>
<td>
#foreach (var exerType in Model.AllExerciseTypes)
{
<label>
#Html.CheckBox("RestrictedType")
#exerType.Name
</label>
}
<input type="submit" value="Add Medical Condition" />
</td>
}
and this is how I'm retrieving values in the controllers
public ActionResult AddMCondition(string txtMCondition, string[] RestrictedType)
{
//Code here...
}
There are only 3 item in the AllExerciseTypes collections. I've notice that each checkbox is sending at least a false value to the controller whether it's selected or not. If I don't check any checkbox, I get 3 false in the collection. If I check 1 checkbox, I get 4 values, i.e. 1 true and 3 falses, and so on. When I check all of them, I get 3 values, i.e. True, False, True, False, True, and False.
Is there any reason, checkboxes are sending at least false in each situation?

Answer 1

This is because the Html Helper for a checkbox adds an extra hidden field with a value of false to ensure that something is posted back to the server even if the checkbox is not checked. If you add <input type="checkbox" name="cbSomething" value="true"/> to your form and post it back without checking the checkbox then you won't get a value sent back to the server. If you use the strongly typed helper extension (Html.CheckBoxFor(m => m.RestrictedType) for example) and bind a checkbox to a property on your model, the model binder will correctly bind the value to the model property. Here's the code snippet from the input extensions within MVC:
if (inputType != InputType.CheckBox)
return TagBuilderExtensions.ToMvcHtmlString(tagBuilder1, TagRenderMode.SelfClosing);
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.Append(tagBuilder1.ToString(TagRenderMode.SelfClosing));
TagBuilder tagBuilder2 = new TagBuilder("input");
tagBuilder2.MergeAttribute("type", HtmlHelper.GetInputTypeString(InputType.Hidden));
tagBuilder2.MergeAttribute("name", fullHtmlFieldName);
tagBuilder2.MergeAttribute("value", "false");
stringBuilder.Append(tagBuilder2.ToString(TagRenderMode.SelfClosing));
return MvcHtmlString.Create(((object) stringBuilder).ToString());