Private Sub ToolBar1_ButtonClick(ByVal sender As System.Object, ByVal e As _
  System.Windows.Forms.ToolBarButtonClickEventArgs) Hendles ToolBar1.ButtonClick
    If e.Button Is ToolBarButtonÖffnen Then
        ' ...
    ElseIf e.Button Is ToolBarButtonSchließen Then
        ' ...
    End If
End Sub

Private Sub ToolBar1_ButtonClick(ByVal sender As System.Object, ByVal e As _
  System.Windows.Forms.ToolBarButtonClickEventArgs) Hendles ToolBar1.ButtonClick
    Select Case e.Button.Tag.ToString
        Case "Öffnen"
            ' ...
        Case "Schließen"
            ' ...
    End Select
End Sub