DropDownList选择发布为空ASP.NET MVC

Question

I have a DropDownList that is populated from a database table that has one column called "IncidentNumber". When using this DropDownList to post as part of a form into a different database table the application is throwing an exception because the DropDownList selection is posting as null. Any help here would be much appreciated!

Controller Action

 var items = db.ViewIncidentNumbers.ToList();
        if (items != null)
        {
            ViewBag.data = items;
        }

        if (ModelState.IsValid)
        {
            using (LogInformationEntities4 dc = new LogInformationEntities4())
            {
                dc.LandLostPersonDetails.Add(land);
                dc.SaveChanges();
            }
         }

Code that is in the View

<div class="form-group">
        @Html.LabelFor(model => model.Incident_Number, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownList("IncidentNumber", new SelectList(ViewBag.data, "IncidentNumber", "IncidentNumber"))
        </div>
    </div>

EDIT: Incident Number class:

    public partial class IncidentNumber
{
    public int Id { get; set; }
    public string IncidentNumber1 { get; set; }
}

My controller currently looks like:

    [HttpGet]
    public ActionResult NewLandMissingPerson()
    {
        string teamsession = string.Empty;
        string username = string.Empty;
        teamsession = Convert.ToString(Session["Callsign"]);
        username = Convert.ToString(Session["Username"]);

        LogInformationEntities4 dc = new LogInformationEntities4();
        var items = dc.IncidentNumbers.ToList();
        ViewBag.data = new SelectList(items.Select(x => new { Text = x.IncidentNumber1, Id = x.Id, Value = x.IncidentNumber1 }).ToList());

        return View();
    }

        [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult NewLandMissingPerson(LandLostPersonDetail land)
    {
        LogInformationEntities4 db = new LogInformationEntities4();
        bool Status = false;
        string response = "";

        var items = db.IncidentNumbers.ToList();
        ViewBag.data = new SelectList(items.Select(x => new { Text=x.IncidentNumber1, Id=x.Id, Value = x.IncidentNumber1 }).ToList());
        if (ModelState.IsValid)
        {
            using (LogInformationEntities4 dc = new LogInformationEntities4())
            {
                dc.LandLostPersonDetails.Add(land);
                dc.SaveChanges();
                response = "New Missing Person Log Added.";
                Status = true;
            }
        }

And the view currently looks like:

@Html.DropDownListFor(model => model.Incident_Number, new SelectList(ViewBag.data, "IncidentNumber1", "IncidentNumber1"))

I am currently getting an exception which says that IncidentNumber1 does not exist in System.Web.Mvc.SelectListItem

Answer 1

 @Html.DropDownListFor(m => m.IncidentNumber, new SelectList(ViewBag.data, "IncidentNumber", "IncidentNumber"))

在Controller中，您必须使用IncidentNumber属性进行访问

Answer 2

Okay, based from the comments, I think this will help.

Since, IncidentNumber is a property of LandLostPersonDetail class, then you should use DropDownListFor instead of DropDownList . DropDownListFor allows for client-side validation based on your model.. so if in your LandLostPersonDetail class.. let's say that IncidentNumber is required.. then if there is no value for that when the form is submitted then validation will occur on the client-side rather than having to wait and go to if (ModelState.IsValid) on the server-side.

Here is what I recommend changing:

In your HttpGet Action

ViewBag.IncidentNumberSelection = new SelectList(db.IncidentNumbers.ToList(), "IncidentNumber1", "IncidentNumber1");

In your View

<div class="form-group">
    @Html.LabelFor(model => model.Incident_Number, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownListFor(model => model.Incident_Number,(IEnumerable<SelectListItem>)ViewBag.IncidentNumberSelection, "-- Select Incident Number --", new { @class = "form-control" })
    </div>
</div>

Then, in your HttpPost actionresult.. you will no longer need:

var items = db.IncidentNumbers.ToList();
ViewBag.data = new SelectList(items.Select(x => new { Text=x.IncidentNumber1, Id=x.Id, Value = x.IncidentNumber1 }).ToList());

Please let me know if this helps.