winform 如何创建mdi--属性IsMdiContainer=true

private void MDI_MainForm_Load(object sender, EventArgs e)
{

frm_DataCenter dtCenter = new frm_DataCenter();

dtCenter.MdiParent = this;
dtCenter.Show();
dtCenter.WindowState = FormWindowState.Maximized;

}

dtCenter.WindowState = FormWindowState.Maximized;
dtCenter.WindowState = FormWindowState.Normal; //原窗体的默认大小