How To Fire Checkbox Checked Event in DropDownCheckBoxes control

I am using DropDownCheckBoxes control in my webpage. I want to show checked items of DropDownCheckBoxes in label control of form. Whenever user checked or unchecked the item, it should get added or removed from list. Also i want to restrict the user to select maximum 8 items.

I have taken reference of below article

https://www.aspsnippets.com/Articles/DropDownCheckBoxes-ASPNet-DropDownList-CheckBoxList-Server-control.aspx

I have searched so many articles over internet for DropDownCheckBoxes controls but no success. Can anyone please tell me?