dynamically call ddl selectedindex change event

I have a global user control thats just a a dropdownlist with values.
Now in one of my web pages where I am using this user control, has one more dropdownlist whose values are dependent on this global one.
How can I add selected index change event to the user control as a property so that in my webpage i can use something like:
ddl.AutoPostback = true;
void ddl_selectedindexchange(.......)
...
Any suggestions, code would be appreciated.
Am using C#.
Thanks
 
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