How to Autotrigger a event/Action?

Hi gurus,

Here I have to display the subtotal for the Amount column.....(Note- its a normal table) ....currently what I am doing is, entering each and every row for amount column and manually pressing enter button (OnAction) , and calculating inside that event handler method and setting to subtotal field...which is not user friendly. Can anybody please give some how to do this automatically.....means whenever I will enter amount in Amount column ....subsequently i have to display the subtotal amount.......hope someone will help me.

thanks & regards

Suman Kumar