Vb.net 下拉列表的默认值

我需要为下拉列表设置一个默认值，如下所示：

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

    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

用户不一定需要选择某些内容，但列表会抛出一个错误

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

具有键“BillId”的ViewData项的类型为“System.Int32”，但必须为“IEnumerable”类型

如果未选择某个值，则该框保持默认空白状态

我的控制器如下所示：

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

    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

函数创建（id为整数）作为ViewResult
ViewBag.id=id
将作业变暗为作业=新作业
job.CustomerId=id
job.JobAmount=0
job.JobDate=Date.Now（）
job.JobStatus=“活动”
Dim BillList=新列表（票据）（）
Dim BillQuery=从s到db.票据
选择s
BillList.AddRange（BillQuery）
ViewBag.BillId=新建选择列表（BillList、“BillId”、“BillDate”）
返回视图（作业）
端函数
'
'发布：/Job/Create
函数创建（作业作为作业）作为操作结果
如果ModelState.IsValid，则
db.Jobs.Add（作业）
db.SaveChanges（）
Dim customer As customer=db.Customers.Find（job.CustomerId）
Dim customerNumber作为字符串=customer.customphone.ToString（）
Dim messageSender As SendMessage=新建SendMessage
Dim smsMessage As String=“洗衣房：工作编号”&Job.JobId&“已预订。当其中的个别服务准备好收取时，您将收到通知。”
messageSender.SendMessage（smsMessage，customerNumber）
Dim url为String=“/RequestedService/AddService/”+job.JobId.ToString（）
返回重定向（url）
如果结束
返回视图（作业）
端函数

如果模型作业没有视图中的BillId属性，则下拉标记应为

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

模型作业包含属性BillId，而不是创建具有不同名称的ViewBag，并在视图标记中相应地使用它们，例如：

在控制器中创建具有不同名称而不是BillId的ViewBag

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

鉴于此，请按如下方式使用

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

---

希望这对你有帮助

我的模型作业确实有BillId，所以我需要给它一个默认值？