How can I make Html.CheckBoxFor() work on a string field?

Question

I'm using ASP.NET MVC3 with Razor and C#. I am making a form builder of sorts, so I have a model that has a collection of the following object:

public class MyFormField
{
    public string Name { get; set; }
    public string Value { get; set; }
    public MyFormType Type { get; set; }
}

MyFormType is just an enum that tells me if the form field is a checkbox, or textbox, or file upload, or whatever. My editor template looks something like this (see the comment):

~/Views/EditorTemplates/MyFormField.cshtml

@model MyFormField
@{
    switch (Model.Type)
    {
        case MyFormType.Textbox:
            @Html.TextBoxFor(m => m.Value)
        case MyFormType.Checkbox:
            @Html.CheckBoxFor(m => m.Value)  // This does not work!
    }
}

I tried casting/converting the m.Value to a bool in the lambda expression for CheckBoxFor(), but that threw an error. I would just manually construct a checkbox input, but CheckBoxFor() seems to do two things that I can't seem to replicate:

1. Creates a hidden input that somehow gets populated by the checkbox. This appears to be what the model binder picks up.
2. Generates the name form the object so that the model binder gets the value into the right property.

Does anyone know a way around using CheckBoxFor() on a string, or a way to replicate its functionality manually, so that I can make this work?

Lax

Answer 1

You could also add a property on your viewmodel:

    public class MyFormField
    {
        public string Name { get; set; }
        public string Value { get; set; }

        public bool CheckBoxValue
        {
            get { return Boolean.Parse(Value); }
        }

        public MyFormType Type { get; set; }
    }

Your view would be something like this:

@model MyFormField
@{
    switch (Model.Type)
    {
        case MyFormType.Textbox:
            @Html.TextBoxFor(m => m.Value)
        case MyFormType.Checkbox:
            @Html.CheckBoxFor(m => m.CheckBoxValue)  // This does work!
    }
}

Use Boolean.TryParse if you want to avoid exceptions.

Lait

Answer 2

One way is to create your own htmlhelper extension method.

    public static MvcHtmlString CheckBoxStringFor<TModel>(this HtmlHelper<TModel> html, Expression<Func<TModel, string>> expression)
    {
        // get the name of the property
        string[] propertyNameParts = expression.Body.ToString().Split('.');
        string propertyName = propertyNameParts.Last();

        // get the value of the property
        Func<TModel, string> compiled = expression.Compile();
        string booleanStr = compiled(html.ViewData.Model);

        // convert it to a boolean
        bool isChecked = false;
        Boolean.TryParse(booleanStr, out isChecked);

        TagBuilder checkbox = new TagBuilder("input");
        checkbox.MergeAttribute("id", propertyName);
        checkbox.MergeAttribute("name", propertyName);
        checkbox.MergeAttribute("type", "checkbox");
        checkbox.MergeAttribute("value", "true");
        if (isChecked)
            checkbox.MergeAttribute("checked", "checked");

        TagBuilder hidden = new TagBuilder("input");
        hidden.MergeAttribute("name", propertyName);
        hidden.MergeAttribute("type", "hidden");
        hidden.MergeAttribute("value", "false");

        return MvcHtmlString.Create(checkbox.ToString(TagRenderMode.SelfClosing) + hidden.ToString(TagRenderMode.SelfClosing));
    }

The usage is the same as CheckBoxFor helper (e.Value is a string)

@Html.CheckBoxStringFor(e => e.Value)

Neologize

I think wrapping the property is the way easier/cleaner way in this situation, but I'll vote you up for this explanation. I've been looking for the code from the first two sections of your method, so thanks for that part! – Lax

Answer 3

Use the Checkbox, this simple way works fine

@Html.CheckBox("IsActive", Model.MyString == "Y" ? true : false)

Ballad

You don't need the ? true : false part. Model.MyString == "Y" is already a boolean. – Mosenthal

Answer 4

I had this problem as well but was unable to modify the view model. Tried mdm20s solution but as i suspected it does not work on collection properties (it does not add the indexes to the names and ids like the native html helpers). To overcome this you can use the Html.CheckBox instead. It adds the proper indexes and you can pass the value of the checkbox yourself.

If you really want to use an expression you can always write a wrapper similar to mdm20s but replace everything after the TryParse with return Html.CheckBox("propertyName", isChecked). Obviously you will need to add using System.Web.Mvc.Html as well.

Vanzandt