How to know Array Index of sender object in Event?

The key information would either be the sender or the Event args. Either the event's data will have the selected item/index or you will have to cast the sender to something else. For example, a ListBox OnSelectedIndexChanged, you will cast the sender as a ListBox and then use the SelectedIndex Property to get that index.

Without more details about the Event and Code, I cannot get more specific.

Thanks,

Brad