Question

After adding the class to the html.dropdownlist am facing the below error.

Error:‘System.Web.Mvc.HtmlHelper’ does not contain a definition for ‘DropDownList’ and the best extension method overload ‘System.Web.Mvc.Html.SelectExtensions.DropDownList(System.Web.Mvc.HtmlHelper, string, string)’ has some invalid arguments

<li>
                    @Html.LabelFor(m => m.BuildType)
                    @Html.DropDownList("BuildType", new { @class = "BuildType" })
                    @Html.ValidationMessageFor(m => m.BuildType)
                </li>
                <li>@Html.LabelFor(m => m.BuildMode)
                    @Html.DropDownList("BuildMode", new { @class = "BuildMode" })
                    @Html.ValidationMessageFor(m => m.BuildMode) </li>
                <li>

Answer 1

You can use:

@Html.DropDownListFor(m => m.BuildType, (SelectList)Viewbag.YourSelectList, "Select Build type", new { @class = "BuildType" })

or

@Html.DropDownListFor(m => m.BuildType, Model.YourSelectList, "Select Build type", new { @class = "BuildType" })

When you use @Html.DropDownList, you specify a name for the dropdownlist… but you are missing the SelectList itself. I think that out of the box, the helper will try to use the name of the DropDownList (in your case “BuildType”) to search in the ViewData collection for the SelectList.

When you use a @Html.DropDownListFor you don’t use a name, but a lamda expression m => m.BuildType that will help you in same cases to not have harcoded names.

Your SelectList (the second parameter) can be grabbed from Viewbag or from a property in your Model.