What is an interface that specifies an enumerable Windows control?

Question

I have a method that validates a combo box control like so:

Public Function ValidateComboBox(ByVal objMessageMode As Errors.MessageMode, ByVal cboInput As ComboBox) As Boolean

    Dim blnValidated As Boolean

    'no value--invalidate'
    If cboInput.SelectedValue Is Nothing Then
        Errors.InvalidateField(cboInput, Errors.errFieldBlank, Me.ErrorProviderPurchaseTag, objMessageMode)
        blnValidated = False

        'value--validate'
    Else
        Errors.ValidateField(cboInput, Me.ErrorProviderPurchaseTag)
        blnValidated = True
    End If

    Return blnValidated

End Function

What I want is to be able to substitute any control as a parameter that implements the behavior of the "SelectedValue" object. Is there an interface that I could specify? Thanks for the help!

Answer 1

ComboBox doesn't implement an interface, but instead inherits from the abstract class ListControl.

Answer 2

I don't believe there is. I've created my own interface (usually I(Product)Field that also contains other helper info) that each different type of control implements. Then, in the validation I just cast to that; it's not the best design in the world but it works like a charm.

Note that this also involves subclassing each type of control (edit box, combo box, etc) but, I'm usually already subclassing them for other purposes so I don't consider this is a problem.