void FrmOMS_FormClosed(object sender, FormClosedEventArgs e)
 {
     if (sender is frmDataCenter)
     {
         frmDataCenter = null;
     }
 }
 private void toolStripMenuItem1_Click(object sender, EventArgs e)
 {
     if (frmDataCenter == null)
     {
         frmDataCenter             = new frmDataCenter();
         frmDataCenter.FormClosed += new FormClosedEventHandler(FrmOMS_FormClosed);
     }
     if (frmDataCenter == null)
     {
         frmDataCenter = new frmDataCenter();
     }
     frmDataCenter.Show(this.dockPanel2);
 }