private void Form1_Load(object sender, System.EventArgs e) { FormBased frm1 = new FormBased(); FrameBased frm2 = new FrameBased(); ControlBased frm3 = new ControlBased(); frm1.MdiParent = this; frm2.MdiParent = this; frm3.MdiParent = this; frm1.Show(); frm2.Show(); frm3.Show(); }