Custom Server Controls :: Want To Implement On Client Side  "onchange" Event?

I have developed and multicolumn combo box server control using textbox and image(for arrow) as described in following sample

http://www.codeproject.com/KB/custom-controls/Multi_Column_Combo_Box.aspx

It is working fine. Now what i want is to implement is client side "onchange" event.

for e.g. if we want to call javascript function on selection change event of dropdownlist control then we can do it as follows

DropDownList1.Attributes("onchange") = "javascript:Validate();"

Here "onchange" is inbuilt client side event for dropdownlist control

Similarly i want such client side event that the is fired when selection is changed in my multicolum control,something like this

MultiColDropDown1.Attributes("onchange") = "javascript:Validate();"