How can I call a sub using visual basic. Net in a web form right after a txtfield is entered/changed? I have tried this but is doesn't do what I wish.

Code:
Private Sub post1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles post1.TextChanged, post1.Unload, post1.DataBinding
        If post1.Text <> "-" Then
            getZip()
        End If
    End Sub