How dropdown find out that its selected index has changed and need to fire selected index changed event?
<p>How dropdown find out that its selected index has changed and need to fire selected index changed event?</p>

<p>Suppose i have a dropdown which is bounded with objectdatasource
and objectdatasource has following items 
opt1
opt2
opt3
opt4
then i added default value --select-- to objectdatasource, now dropdown is populated and i can see all the items on it. I have a button and on its client click, through java script i set opt4 to selected item. now if i select --select-- from dropdown then it does not fire selected index changed event but it fires dropdown's data bound event and then if i select any other value it fire both events and then if i again select --select-- then it fire both event, only first time if i select --select--then it will not fire selected index change event but if i select other than --select-- it fire both events.</p>

<p>So my question is how dorpdown find out that its selection index has changed.</p>
