Trouble with MVC ListBox

Question

So I have an MVC application in which I'm trying to display a list of items in a ListBox, allowing the user to add or remove items as needed. Here's what's happening:

This is my Get, in which I create the SelectList to show in the ListBox in the View:

' GET: Trucks/Edit/5
Async Function Edit(ByVal id As Integer?) As Task(Of ActionResult)
    ....
    Dim curItems As SelectList
    If truck.Items IsNot Nothing Then
        curItems = New SelectList(truck.Items, "ID", "Name")
    Else
        curItems = New SelectList("")
    End If
    ViewData("ItemNames") = curItems
    Return View(truck)
End Function

So then this is my Edit View:

@ModelType myproject.Truck
@Code
    ViewData("Title") = "Edit"

    Dim ItemNames As SelectList
    ItemNames = ViewData("ItemNames")
End Code

<h2>Edit Truck</h2>

@Using (Html.BeginForm("Edit", "Trucks", FormMethod.Post, New With {.name = "frmTruckEdit", .id = "frmTruckEdit"}))
    @Html.AntiForgeryToken()

    @<div class="form-horizontal">
        <hr />
        <div class="text-danger">@(ViewData("TError"))</div>

        @Html.ValidationSummary(True, "", New With {.class = "text-danger"})
        @Html.HiddenFor(Function(model) model.ID)
         <br />
....
         <div class="form-group">
             <div class="control-label col-md-2" style="font-weight: bold">Items for this Truck</div>
             <div class="col-md-10">
                 @Html.ListBox("ItemNames", New SelectList(ItemNames), htmlAttributes:=New With {.id = "ItemNames", .class = "mylistbox"})
             </div>
             <div class="col-md-offset-2 col-md-10">
                 <br />
                 <div class="btn-link" id="RemoveItem">Remove Selected Item</div>
             </div>
         </div>

    <br />
        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </div>
    </div>  End Using

So trying it this way, where I specify New SelectList(ItemNames) in the ListBox arguments, the items in the ListBox show as "System.Web.Mvc.SelectListItem".

If I simply remove the "New SelectList" so that argument is just ItemNames, the items in the ListBox show correctly (the name text), however, when I hit Post, I get error

There is no ViewData item of type 'IEnumerable< SelectListItem >' that has the key 'ItemNames'

Note: I also tried using it as an IEnumerable(Of SelectListItem) instead. 'New' can't be used with that so I can't try specifying "New IEnumerable(ItemNames)" in the ListBox, and just "ItemNames" gives me the same error about no ViewData item.

I am at a loss right now as to what I'm doing wrong here. Let me know if you need more info. Thank you!!

It would need to be `New SelectList(ItemNames, "Value", "Text")` in the `ListBox()` method, but that would be pointless - its already a `SelectList` so no need to create another identical one. But there are numerous other issues with your code including that your cannot use the same name for the property your bingding to and the `SelectList` (refer [this answer](http://stackoverflow.com/questions/37161202/will-there-be-any-conflict-if-i-specify-the-viewbag-name-to-be-equal-to-the-mode/37162557#37162557)) — , Mar 18 '17 at 23:02
And the _There is no ViewData item..._ error is thrown because you do not repopulate the `SelectList` in the POST method before you return the view (as you did in the GET method). Use a view model with a property `IEnumerable` and a property for the `SelectList` (refer [this question/answer](http://stackoverflow.com/questions/34366305/the-viewdata-item-that-has-the-key-xxx-is-of-type-system-int32-but-must-be-o) for the correct approach) — , Mar 18 '17 at 23:04
@StephenMuecke - OK so I changed the name, and I added populating the ViewData item in Post. Now the items in the listbox look right and I can post without getting that error. What are more of these 'numerous other issues' with my code? — Andy, Mar 19 '17 at 19:31

Trouble with MVC ListBox

0 Answers0