private void barButtonItem1_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e) { if (!this.MdiChildren.OfType <FrmDemirbaslar>().Any()) { FrmDemirbaslar demirbas = new FrmDemirbaslar(); demirbas.Owner = this; demirbas.MdiParent = this; demirbas.Show(); } }