Hi Michael ,
If you want to hide the dropdown of comboDropDown control then you can use HidePopup() method of its PopupContainer. Please refer to the following code snippet.
this.userControl11.radioButton1.CheckedChanged += new EventHandler(radioButton1_CheckedChanged);
void radioButton1_CheckedChanged(object sender, EventArgs e)
{
this.comboDropDown1.PopupContainer.HidePopup();
}
Please refer to the attached sample that illustrates this.
http://websamples.syncfusion.com/samples/Tools.Windows/41965/main.htmPlease let me know if you have any other questions.
Regards,
Nagaraj