Html.DropDownListFor() with custom parameter

Question

I want to add extension method in HTML helpers for generating select and options like this

<select id="Country" name="Country">
<option data-domain="AN" value="1">Andorra</option>
<option data-domain="UI" value="2">United Arab Emirates</option>
<option data-domain="AF" value="3">Afghanistan</option>

the options have a data-domain attribute, and I can use it like this

@Html.DropDownListFor(m => m.Country, Model.CountryList)

the Model.CountryList is an arrayh of Country valiables

class Country
{
    public String Text { get; set; }
    public String Value { get; set; }
    public String Domain { get; set; }
}

please can anyone give a solution

Answer 1

You can build your CustomDropdownListFor with the help of a custom helper method as shown below:

Custom Helper Method:

public static class CustomHelpers
{    
    public class CustomSelectItem : SelectListItem
    {           
        public string Class { get; set; } 
        public string Disabled { get; set; }
        public string SelectedValue { get; set; }
    }

    public static MvcHtmlString CustomDropdownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<CustomSelectItem> list, string selectedValue, string optionLabel, object htmlAttributes = null)
    {
        if (expression == null)
        {
            throw new ArgumentNullException("expression");
        }
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression<TModel, TProperty>(expression, htmlHelper.ViewData);
        string name = ExpressionHelper.GetExpressionText((LambdaExpression)expression);
        return CustomDropdownList(htmlHelper, metadata, name, optionLabel, list, selectedValue, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
    }

    private static MvcHtmlString CustomDropdownList(this HtmlHelper htmlHelper, ModelMetadata metadata, string name, string optionLabel, IEnumerable<CustomSelectItem> list, string selectedValue, IDictionary<string, object> htmlAttributes)
    {
        string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
        if (String.IsNullOrEmpty(fullName))
        {
            throw new ArgumentException("name");
        }

        TagBuilder dropdown = new TagBuilder("select");
        dropdown.Attributes.Add("name", fullName);
        dropdown.MergeAttribute("data-val", "true");
        dropdown.MergeAttribute("data-val-required", "Mandatory field.");
        dropdown.MergeAttribute("data-val-number", "The field must be a number.");          
        dropdown.MergeAttributes(htmlAttributes); //dropdown.MergeAttributes(new RouteValueDictionary(htmlAttributes));
        dropdown.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata)); 

        StringBuilder options = new StringBuilder();

        // Make optionLabel the first item that gets rendered.
        if (optionLabel != null)
            options.Append("<option value='" + String.Empty + "'>" + optionLabel + "</option>");

        foreach (var item in list)
        {
            if (item.SelectedValue == "selected" && item.Disabled == "disabled")
                options.Append("<option value='" + item.Value + "' class='" + item.Class + "' selected='" + item.SelectedValue + "' disabled='" + item.Disabled + "'>" + item.Text + "</option>");
            else if (item.SelectedValue != "selected" && item.Disabled == "disabled")
                options.Append("<option value='" + item.Value + "' class='" + item.Class + "' disabled='" + item.Disabled + "'>" + item.Text + "</option>");
            else if (item.SelectedValue == "selected" && item.Disabled != "disabled")
                options.Append("<option value='" + item.Value + "' class='" + item.Class + "' selected='" + item.SelectedValue + "'>" + item.Text + "</option>");
            else
                options.Append("<option value='" + item.Value + "' class='" + item.Class + "'>" + item.Text + "</option>");
        }
        dropdown.InnerHtml = options.ToString();
        return MvcHtmlString.Create(dropdown.ToString(TagRenderMode.Normal));
    }
}

View (Razor):

@Html.CustomDropdownListFor(m => m.PersonId, ViewBag.PersonData as List<CustomHelpers.CustomSelectItem>, null, "---- Select ----", 
    new { name = "personId", id = "personId"})                   
@Html.ValidationMessageFor(m => m.PersonId, null , new { @class = "ValidationErrors" })

Hope this helps...

Answer 2

The standard DropDownList/DropDownListFor helpers do not support this. You will have to write a custom HTML helper from scratch if you need such functionality. You may checkout this example. And another one.

Answer 3

Method:

 public static MvcHtmlString DropDownList(this HtmlHelper htmlHelper, string name, IEnumerable<SelectListCodeItem> selectList)
        {
            var select = new TagBuilder("select");

            var options = "";
            TagBuilder option;

            foreach (var item in selectList)
            {
                option = new TagBuilder("option");
                option.MergeAttribute("value", item.Value.ToString());
                option.MergeAttribute("data-domain", item.Code.ToString());
                option.SetInnerText(item.Text);
                options += option.ToString(TagRenderMode.Normal) + "\n";
            }

            select.MergeAttribute("data-val", "true");
            select.MergeAttribute("data-val-required", "The field is required.");
            select.MergeAttribute("id", name);
            select.MergeAttribute("name", name);

            select.InnerHtml = options;

            return new MvcHtmlString(select.ToString(TagRenderMode.Normal));
        }

Call:

@Html.DropDownList("name" Model.OrganizationTypeList)