登录窗体为主线程窗体时实现重登录的一个困难

 if (new UserService().loginCheckWithSqlparameters(txt_userID.Text, pwd))
                    {
                        CurrentUser.userID = txt_userID.Text;
                        //AuthorizationEventArgs a = new AuthorizationEventArgs();
                        //a.userAndPwdRight = true;
                        //onAuthorizPass(a);
                        DialogResult = DialogResult.OK;

                        //if (loginSuccessFlag==true)
                        //{

                        //}
                        //Frm_main f = new Frm_main();

                        //f.Show();
                        //loginSuccessFlag = true;

                        //登录成功后隐藏登录窗体
                        //this.Hide();
                        ////主窗体关闭后登录窗体也关闭
                        //f.FormClosed += closeLoginForm;
                        ////主窗体点击重登录时，调出登录窗体
                        //f.重登录ToolStripMenuItem.Click += 重登录ToolStripMenuItem_Click;
                    }

   [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            Frm_login frm_Login = new Frm_login();

            frm_Login.ShowDialog();
            if (frm_Login.DialogResult == DialogResult.OK)
            {
                Application.Run(new Frm_main());
            }
            else
            {
                Application.Exit();
            }


        }