Combobox cancel dropdown
private void comboBox1_DropDown(object sender, EventArgs e)
    {
        valSel.incBox = (ComboBox)sender;
        valSel.Show();
        if (this.comboBox1.DroppedDown)
        {
            MessageBox.Show("test");
            SendMessage(this.comboBox1.Handle, CB_SHOWDROPDOWN, 0, 0);
        }
    }