.NET Compact Framework.代码展开ComboBox下拉选项

.NET Framework中可以用this.comboBox1.DroppedDown=true;来展开Combobox。
但Windows Mobile 用的.NET Compact Framework中不支持ComboBox.DroppedDown这一属性。
.NET Compact Framework中可以用以下代码实现展开ComboBox：

        private const uint CB_SHOWDROPDOWN = 0x014f;
        private const int TRUE = 1;
        private const int FALSE = 0;

        [DllImport("Coredll.dll", EntryPoint = "SendMessage", SetLastError = true)]
        private static extern int SendMessage(IntPtr hWnd, uint msg, int wParam, int
        lParam);
       
        private void btn_MouseDown(object sender, MouseEventArgs e)
        {
            SendMessage(this.comboBox1.Handle, CB_SHOWDROPDOWN, TRUE, 0);
        }