Validar un texbox

[kaliche]

yo quiero validar que cuando se ingrese el codigo de barra

me diga si existe en la base de datos lo hago con el evento txtbarra_lostfocus

ayuda?

Private Sub txtbarra_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtbarra.LostFocus
Connection.Open()
Try
Dim da As SqlDataAdapter
Dim dt As New DataTable
Dim ds As New DataSet
Dim b As String
Dim s As String = "SELECT codigo_barra FROM articulo WHERE codigo_barra = '" & txtbarra.Text & "'"
da = New SqlDataAdapter(s, Connection)
da.Fill(dt)

If s = "" Then
b = CStr(1)
If txtbarra.Text <> b Then
MsgBox("no existe el articulo")
Else
MsgBox(" existe el articulo")
End If

End If

Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
Connection.Close()
End Sub