如何使ASP.NET TextBox在AJAX UpdatePanel中触发onTextChanged事件？

I am trying to get an textBox to fire it's onTextChanged event every time a keystroke is made rather than only firing only when it looses focus. I thought that adding the AsyncPostBackTrigger would do this but it's still not working. Is what I'm trying to do even possible? The code is below:I am trying to get an textBox to fire it's onTe