如何在添加新行后在gridview中保留行值？

I have a gridview with textboxes for item no, desc qty, cost, extncost. When itemno entered in the textbox desc and cost of the item will comes automatically by on textbox event change. Here when i add a new row in the grid view, values of last entered value got disappears. when i am checking using break point i can able to see the last entered values in data table. Since, while adding new row has blank text boxes, now system considers blank text box for on text change event. So, last entered values also not displaying. Text box changes in one row also affects in other rows.I have a gridview with textboxes for item no, d