Nerdy Dork

I’ve had this problem for a couple days and I told myself that if I found the solution I would post it on this blog. Basically, what I have is a ComboBox control which has a data binding to its SelectedValue.

I’ve figured out how to populate the ComboBox with my own custom list using a custom built class and an ArrayList.

Here is my class:
Public Class SkewValues
Private iValue As Integer
Private sDisplay As String

Public Sub New(ByVal Value As Integer, ByVal Display As String)
Me.iValue = Value
Me.sDisplay = Display
End Sub ‘New

Public ReadOnly Property Value() As Integer
Get
Return iValue
End Get
End Property

Public ReadOnly Property Display() As String
Get
Return sDisplay
End Get
End Property
End Class

Populating the ArrayList:
Dim Skews As New ArrayList
Skews.Add(New SkewValues(0, "Up to 5 Degrees"))
Skews.Add(New SkewValues(1, "13 Degrees"))
Skews.Add(New SkewValues(2, "21 Degrees"))
Skews.Add(New SkewValues(3, "29 Degrees"))
Skews.Add(New SkewValues(4, "37 Degrees"))
Skews.Add(New SkewValues(5, "45 Degrees"))

And setting the DataSource:
Me.cboSkewTolerance.DataSource = Skews
Me.cboSkewTolerance.ValueMember = "Value"
Me.cboSkewTolerance.DisplayMember = "Display"

This worked so far as populating the list, letting me select the value, and updating the database. The problem was that when I loaded the form it wouldn’t display the right value, and after selecting a value, it would disappear as soon as the ComboBox lost focus.

The Odd thing was I was having the problem in two locations on my application and the cause was essentially the same, but different.

The first problem was that with the code above, in my SkewValues class, I was returning a string for my Value property (accident) and the value it was bound to was expecting an integer. So there were no errors or warnings, just that quirk of not displaying what was selected.

This was essentially the same issue I had elsewhere - the DataBinding expected value was not the same type as what was in the ArrayList.

It is really essential that the DataType in the DataBinding and the DataSource be of the same type. I had another issue were the bound data was Int64 (created by the designer based on my database) and my DataSouce value was an Integer. Once I changed my DataTableAdapter so the bound data was and Int32 it worked as expected.

On other issue that I had to resolve was that the value was populated initially, but it was wrong. For this, I called SuspendBinding on the BindingSource before setting the ComboBox.DataSource, and then ResumeBinding when I was done - like so:

Me.ZonesBindingSource.SuspendBinding()
Dim FieldVals As New ArrayList
For i As Integer = 0 To DocGroup.Schemas.Count - 1
FieldVals.Add(New FieldValues(i, DocGroup.Schemas(i).Label))
Next
With Me.cboKfField
.DataSource = FieldVals
.ValueMember = "Value"
.DisplayMember = "Display"
End With
Me.ZonesBindingSource.ResumeBinding()

I hope this makes sense to whomever was searching this out. If you have questions, feel free to email me, or leave a comment and I will get an email notification.

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