SelectList Data Annotation claimed as empty or not selected?

Question

Hi All, I don't understand why my SelectList Data Annotation claimed as empty or not selected?

**my.cls**
public class Data
{
    [Required]
    [Display(Name = "Contact Group")]
    public SelectList contactGroupsList { get; set; }

    [Required]
    [Display(Name = "Contact Name")]
    public string contactName { get; set; }

    [Required]
    [Display(Name = "Contact Person Name")]
    public string contactPicName { get; set; }
}

**my.cshtml**
@Html.DropDownListFor(x => x.contactGroupsList, 
    Model.contactGroupsList, "", 
    new { @id = "contactGroupsList", 
    @class = "form-select" })
<span asp-validation-for="contactGroupsList" class="text-danger"></span>


**Controller**

 if (!ModelState.IsValid)
 {
     var errors = ModelState.SelectMany(x => x.Value.Errors.Select(e => new { Field = x.Key, ErrorMessage = e.ErrorMessage }));
     return Json(new { result = false, errors = errors, message = "" });
 }
``

Answer 1

@AgaveJoe

So do you have any idea how to deal with this?, we start the @Html.DropDownListFor to avoid user to select the 1st option, user might accidentally select it so that's why I put "" but we have to check if they select the empty ones.

my.cshtml

@Html.DropDownListFor(x => x.contactGroupsList, Model.contactGroupsList, "", new { @id = "contactGroupsList", @class = "form-select" }) <span asp-validation-for="contactGroupsList" class="text-danger"></span>

Answer 2

So do you have any idea how to deal with this?

To put it simply, when using HTML helpers like DropDownListFor, you need to understand how they create HTML <select> elements. This involves two key parts:

1. The visible choices (options): These are the items the user sees in the dropdown list.
2. The chosen value (selected value): This is the value that gets submitted when the form is sent.

The name attribute of the DropDownListFor corresponds to the property in your model that has the [Required] attribute. This property holds the selected value. The options themselves are just a collection of items used to build the dropdown list.

Model

public class ContactListModel
{
    [Required]
    public string SelectedContact { get; set; }
}

View

@model MvcDemo.Models.ContactListModel
@{
    ViewBag.Title = "Index";
}

<h2>Index</h2>
<div class="container">
    <form method="post">
        <div>
            @Html.DropDownListFor(model => model.SelectedContact, (SelectList)ViewBag.ContactGroupsList)
            @Html.ValidationMessageFor(model => model.SelectedContact)
        </div>
        <div>
            <input type="submit" value="submit" name="submit"/>
        </div>
    </form>
</div>

Controller

public class HtmlSelectExampleController : Controller
{
    private SelectList contactGroupsList {get;set;}

    // GET: HtmlSelectExample
    [HttpGet]
    public ActionResult Index(string id)
    {
        if (string.IsNullOrEmpty(id))
        {
            id = string.Empty;
        }
        ContactListModel model = new ContactListModel() { SelectedContact = id };
        ViewBag.ContactGroupsList = PopulateOptions();
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(ContactListModel model)
    {
        ViewBag.ContactGroupsList = PopulateOptions();
        if (!ModelState.IsValid)
        { 
            return View();
        }
        return RedirectToAction("Index", "HtmlSelectExample", new { id= model.SelectedContact});
    }


    private SelectList PopulateOptions()
    {
        return new SelectList(new List<SelectListItem>
        {
            new SelectListItem { Text = "--Select--", Value = "" },
            new SelectListItem { Text = "Option 1", Value = "1" },
            new SelectListItem { Text = "Option 2", Value = "2" },
            new SelectListItem { Text = "Option 3", Value = "3" }
        }, "Value", "Text");    
    }
}

Answer 3

Hi @AgaveJoe

I try this, but the SelectList still claimed as empty although I don't set it as required as the snippet code below

@Html.DropDownListFor(x => x.selectedContactGroup, 
    Model.contactGroupsList, "", 
    new { @id = "contactGroupsList", 
    @class = "form-select" })
    <span asp-validation-for="selectedContactGroup" class="text-danger"></span>

[Required]
[Display(Name = "Contact Group")]
public string selectedContactGroup { get; set; }

public SelectList contactGroupsList { get; set; } 


Controller

if (!ModelState.IsValid)
{
    var errors = ModelState.SelectMany(x => x.Value.Errors.Select(e => new { Field = x.Key, ErrorMessage = e.ErrorMessage }));
    return Json(new { result = false, errors = errors, message = "" });
}