Question

I need to set a default value for the DropDown list as follows:

@Html.DropDownList("BillId", "") 

The user doesn’t necessarily need to select something but the list throws an error

The ViewData item that has the key 'BillId' is of type 'System.Int32' but must be of type 'IEnumerable<SelectListItem>'

if a value is not selected and the box is left on it’s default blank state.

My controllers as follows:

    Function Create(id As Integer) As ViewResult
        ViewBag.id = id
        Dim job As Job = New Job
        job.CustomerId = id
        job.JobAmount = 0
        job.JobDate = Date.Now()
        job.JobStatus = "Active"

        Dim BillList = New List(Of Bill)()

        Dim BillQuery = From s In db.Bills
                        Select s

        BillList.AddRange(BillQuery)

        ViewBag.BillId = New SelectList(BillList, "BillId", "BillDate")

        Return View(job)
    End Function

    '
    ' POST: /Job/Create

    <HttpPost()>
    Function Create(job As Job) As ActionResult
        If ModelState.IsValid Then
            db.Jobs.Add(job)
            db.SaveChanges()

            Dim customer As Customer = db.Customers.Find(job.CustomerId)
            Dim customerNumber As String = customer.CustCellphone.ToString()
            Dim messageSender As SendMessage = New SendMessage
            Dim smsMessage As String = "LAUNDRY: Job Number " & job.JobId & " has been booked in. You will be notified when individual services within it are ready for collection."
            messageSender.SendMessage(smsMessage, customerNumber)

            Dim url As String = "/RequestedService/AddService/" + job.JobId.ToString()
            Return Redirect(url)
        End If
        Return View(job)
    End Function

Answer 1

If your model Job doesn’t have the property of BillId than in the view the dropdown markup should be

@Html.DropDownList("Job_BillId", ViewBag.BillId)

And the model Job contains the property BillId than create the ViewBag with some different name and use them accordingly in view markup for example:

Create a ViewBag with different name instead of BillId in controller

ViewBag.BillIdList =  New SelectList(BillList, "BillId", "BillDate")

And in view use this as below

@Html.DropDownListFor(model => model.BillId, ViewBag.BillIdList)

Hope this will help you.