ASP.NET C# Set OnSelectedIndexChanged from Code Behind

Im trying to set the SelectedIndexChanged from the code behind of a Web Forms application. I have a variable amount of dropdowns being added onto the page from the database and need a method to trigger each time one of the dropdowns change.

Im currently trying:

ddlProductCause.SelectedIndexChanged += new EventHandler(ddlProductCause_Changed);
ddlProductCause.ID = "ddlProductCause_" + row["item_id"].ToString();
ddlProductCause.AutoPostBack = true;

and...

public void ddlProductCause_Changed(object sender, CommandEventArgs e)
    {
        // do stuff
    }

But I have no luck.

Any ideas?