panel2.Controls.Clear();            frm.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;            frm.ShowIcon = false;            frm.ShowInTaskbar = false;            frm.BackColor = Color.White;            //要将是否顶级控件设置为false，否则会报错            frm.TopLevel = false;            frm.Dock = DockStyle.Fill;            panel2.Controls.Add(frm);            ////TabPage tab = new TabPage(frm.Name);            ////tab.Controls.Add(frm);            ////tabControl1.TabPages.Add(tab);            ////tab.Show();            frm.Show();            frm.BringToFront();            frm.Focus();