' This method is called by the ExtractRowValues methods of
' GridView and DetailsView. Retrieve the current value of the 
' cell from the Checked state of the Radio button.
Public Overrides Sub ExtractValuesFromCell( _
    ByVal dictionary As IOrderedDictionary, _
    ByVal cell As DataControlFieldCell, _
    ByVal rowState As DataControlRowState, _
    ByVal includeReadOnly As Boolean)
    ' Determine whether the cell contain a RadioButton 
    ' in its Controls collection.
    If cell.Controls.Count > 0 Then
        Dim radio As RadioButton = CType(cell.Controls(0), RadioButton)

        Dim checkedValue As Object = Nothing
        If radio Is Nothing Then
            ' A RadioButton is expected, but a null is encountered.
            ' Add error handling.
            Throw New InvalidOperationException( _
                "RadioButtonField could not extract control.")
        Else
            checkedValue = radio.Checked
        End If


        ' Add the value of the Checked attribute of the
        ' RadioButton to the dictionary.
        If dictionary.Contains(DataField) Then
            dictionary(DataField) = checkedValue
        Else
            dictionary.Add(DataField, checkedValue)
        End If
    End If
End Sub