.NET MDI(only one form)

1.Show method.
int index = Opened(this, "FrmMytest");

if (index == -1)
           

{
               

  FrmMytest frmMytest = new FrmMytest();


 frmMytest.MdiParent = this;
               

     frmMytest.Show();
           

}
           

else
           
{
               
     this.MdiChildren[index].Show();
           
}


        public static int Opened(Form frmMdiFather, string strMdiChild)
        {
            int bReturn = -1;
            for (int i = 0; i < frmMdiFather.MdiChildren.Length; i++)
            {
                if (frmMdiFather.MdiChildren[i].Name == strMdiChild)
                {
                    frmMdiFather.MdiChildren[i].BringToFront();
                    bReturn = i;
                    break;
                }
            }
            return bReturn;
        }


2.use singleton method
Mainform中调用的代码：
try
            {
                FrmLot objfrmbl = FrmLot.getInstance();
                objfrmbl.MdiParent = this;
                objfrmbl.WindowState = FormWindowState.Maximized;
                objfrmbl.Show();
                objfrmbl.BringToFront();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

FrmLot 的方法及实例化:
         private string MaterialName = String.Empty;
        private string Route = String.Empty;
        private string RouteVersion = String.Empty;
        private string StepOperationName = String.Empty;
        private string StepName = String.Empty;
        private static FrmLot objfrmCL = null;

        protected FrmLot()
        {
            InitializeComponent();
        }

        public static FrmLot getInstance()
        {
            if (objfrmCL == null)
            {
                lock (typeof(FrmLot))
                {
                    if (objfrmCL == null)
                    {
                        objfrmCL = new FrmLot();
                    }
                }
            }
            return objfrmCL;
        }