Binding data to a combobox and add a select option - vb.net

Question

I'm using VB.NET and Visual Studio 2010
I've got a windows form with a combobox.
I fill the combobox using the following
Dim objSizes As List(Of ASME_Hub_Sizes) = ASME_Hub_Sizes.GetAllHubSizes()
If Not objSizes Is Nothing Then
With Me.cboSize
.DisplayMember = "Size"
.ValueMember = "ID"
.DataSource = objSizes
End With
End If
This works fine, but i would like to add a "Select Size..." option but i'm unsure how to do this.
It seems so much easier to do this in asp.net, but this has me baffled
Thanks
Mick

Answer 1

You could try adding a custom objSize object to the objSizes collection that has ID = 0 and value = "Select size..." as it's ID 0 it should be at the top (I think) and won't clash with any values in your database, upon saving the record you can validate the combobox to avoid writing the "Select size..." object to your database. I'll have a bit of a code and see if this will work...
Ok, I've had another look. You can do as I suggested but you must sort the list before passing it to the combobox. Here is my example:
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
With Me.ComboBox1
.DisplayMember = "Description"
.ValueMember = "ID"
.DataSource = GetListOfObjects.returnListOFObjects
End With
End Sub
End Class
Public Class dummyObjectForCombo
Public Property ID As Integer
Public Property Description As String
Public Sub New(ByVal id As Integer,
ByVal description As String)
_ID = id
_Description = description
End Sub
End Class
Public Class GetListOfObjects
Public Shared Function returnListOFObjects() As List(Of dummyObjectForCombo)
Dim col As New List(Of dummyObjectForCombo)
Dim obj0 As New dummyObjectForCombo(-1, "Herp")
Dim obj1 As New dummyObjectForCombo(1, "Jamie")
Dim obj2 As New dummyObjectForCombo(2, "Bob")
col.Add(obj1)
col.Add(obj2)
col.Add(obj0)
'using a lambda to sort by ID as per http://stackoverflow.com/questions/3309188/c-net-how-to-sort-a-list-t-by-a-property-in-the-object
Return col.OrderBy(Function(x) x.ID).ToList
End Function
End Class
I've used -1 as the topmost record instead of 0.
So you'd get your list as usual, add in the extra dummy record, then sort it as per the above code before assigning it as your combo boxes datasource.

Answer 2

simply add the item before setting the datasource property
C# : cboSize.items.add(...);