public partial class Form1 : Form
    {
        ToolStripDropDown ddown;
        Popup popup;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Click(object sender, EventArgs e)
        {
            ddown = new ToolStripDropDown();
            popup = new Popup();
            ToolStripControlHost dhost = new ToolStripControlHost(popup);
            dhost.AutoSize = false;
            ddown.Items.Add(dhost);
            ddown.Region = popup.Region;
            ddown.Visible = true;
        }
    }

if (mPopup==null)