asp.net core dropdown list not setting selected value

Question

I have a bootstrap drop down and I am using tag helpers to enter render values and read them on post. Below is the code

asp-for="CfgType" -- value is set to SIN or UN based on that set the view to the selected value -- and on submittig the page I need to get the selected value for the drop down from CfgType property.

                <div class="form-row">
                    <div class="col-md-12">
                        <div class="form-group form-group--float">
                            <div class="form-group form-group--float">
                                <select id="dwType" class="form-control  custom-select" asp-for="CfgType">
                                    @if(Model.VehFlg)
                                    {
                                        <option value="SIN">Serial Num</option>
                                    }
                                    
                                    @if(Model.VinFlg)
                                    {
                                        <option value="UN">Unit Number</option>
                                    }

                               </select>
                                <label> Configuration Type</label>
                                <div class="invalid-tooltip"><span asp-validation-for="CfgType"></span></div>
                            </div>
                            <i class="form-group__bar"></i>
                        </div>

Below is how the value is being tried to retrive using controller

//now for fvIdentViewModel.CfgType is null

  [Route("/fv-identification/Save"), HttpPost, ValidateAntiForgeryToken]
 public IActionResult Save(FleetVehicleIdentificationViewModel fvIdentViewModel)
        {

}

Answer 1

Here is a working demo:

Model:

public class FleetVehicleIdentificationViewModel
{
    public string CfgType { get; set; }
    public bool VehFlg { get; set; }
    public bool VinFlg { get; set; }
}

View(Index.cshtml):

@model FleetVehicleIdentificationViewModel
<form action="/fv-identification/Save" method="post">

    @Html.AntiForgeryToken()

    <div class="form-row">
        <div class="col-md-12">
            <div class="form-group form-group--float">
                <div class="form-group form-group--float">
                    <select id="dwType" class="form-control  custom-select" asp-for="CfgType">
                        @if (Model.VehFlg)
                        {
                            <option value="SIN">Serial Num</option>
                        }

                        @if (Model.VinFlg)
                        {
                            <option value="UN">Unit Number</option>
                        }

                    </select>
                    <label> Configuration Type</label>
                    <div class="invalid-tooltip"><span asp-validation-for="CfgType"></span></div>
                </div>
                <i class="form-group__bar"></i>
            </div>
            <div>
                <input type="submit" value="create" />
            </div>
        </div>
    </div>
</form>

Controller:

For easy testing,I set the value manually to render your Index.cshtml :

public IActionResult Index()
{
    var model = new FleetVehicleIdentificationViewModel()
    {
        VehFlg = true,
        VinFlg = false
    };
    return View(model);
}

Your post action:

[Route("/fv-identification/Save"), HttpPost, ValidateAntiForgeryToken]
public IActionResult Save(FleetVehicleIdentificationViewModel fvIdentViewModel)
{
    //do your stuff...
}

Result:

Answer 2

you should put in tag form with button type submit.

<form action="/fv-identification/Save" method="post">
 <button type="submit" class="btn btn-info">@localizer["Submit"] </button>
</form>