去掉Mdi子窗体的标题栏

    Form2 frm = new Form2();
    frm.MdiParent = this;
    frm.FormBorderStyle = FormBorderStyle.None;
    frm.ControlBox = false;
    frm.MinimizeBox = false;
    frm.MaximizeBox = false;
    frm.Show();
    frm.Dock = DockStyle.Fill;
...