devexpress aspxgridview asp.net "CustomButtonInitialize" hide/show custom buttons

protected void ASPxGridView1_CustomButtonInitialize(object sender, DevExpress.Web.ASPxGridViewCustomButtonEventArgs e)
{
if (e.ButtonID == "btnDegistir")
{
if (((ASPxGridView)sender).GetRowValues(e.VisibleIndex, "OnayDurumu").ToString() != "Bekliyor")
e.Visible = DefaultBoolean.False;
}
}