Checkbox for nullable boolean

Question

My model has a boolean that has to be nullable

public bool? Foo
{
   get;
   set;
}

so in my Razor cshtml I have

@Html.CheckBoxFor(m => m.Foo)

except that doesn't work. Neither does casting it with (bool). If I do

@Html.CheckBoxFor(m => m.Foo.Value)

that doesn't create an error, but it doesn't bind to my model when posted and foo is set to null. Whats the best way to display Foo on the page and make it bind to my model on a post?

Answer 1

@{  bool testVar = ((bool)item.testVar ? true : false); }
  @Html.DisplayFor(modelItem => testVar)

Answer 2

Checkbox only offer you 2 values (true, false). Nullable boolean has 3 values (true, false, null) so it's impossible to do it with a checkbox.

A good option is to use a drop down instead.

Model

public bool? myValue;
public List<SelectListItem> valueList;

Controller

model.valueList = new List<SelectListItem>();
model.valueList.Add(new SelectListItem() { Text = "", Value = "" });
model.valueList.Add(new SelectListItem() { Text = "Yes", Value = "true" });
model.valueList.Add(new SelectListItem() { Text = "No", Value = "false" });

View

@Html.DropDownListFor(m => m.myValue, valueList)

Answer 3

I had a similar issue in the past.

Create a Checkbox input in HTML, and set the attribute name="Foo" This should still post properly.

<input type="checkbox" name="Foo" checked="@model.Foo.Value" /> Foo Checkbox<br />

Answer 4

This is an old question, and the existing answers describe most of the alternatives. But there's one simple option, if you have bool? in your viewmodel, and you don't care about null in your UI:

@Html.CheckBoxFor(m => m.boolValue ?? false);

Answer 5

Extension methods:

        public static MvcHtmlString CheckBoxFor<TModel>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, bool?>> expression)
        {
            return htmlHelper.CheckBoxFor<TModel>(expression, null);
        }
        public static MvcHtmlString CheckBoxFor<TModel>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, bool?>> expression, object htmlAttributes)
        {
            ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
            bool? isChecked = null;
            if (metadata.Model != null)
            {
                bool modelChecked;
                if (Boolean.TryParse(metadata.Model.ToString(), out modelChecked))
                {
                    isChecked = modelChecked;
                }
            }
            return htmlHelper.CheckBox(ExpressionHelper.GetExpressionText(expression), isChecked??false ,  htmlAttributes);
        }

Answer 6

I have bool? IsDisabled { get; set; } in Model. Inserted if in View.

<div class="inputClass" id="disabled">
    <div>
    @if(Model.IsDisabled==null)
    {
        Model.IsDisabled = false;
    }           
    @Html.CheckBoxFor(model => model.IsDisabled.Value)         
    </div>
</div>