Gridview row addition should not refresh

Hello All,

I am searching a vin number from database table and adding one by one to gridview (Wheni am entering or selecting in dropdown in the search row), when i add the new row the old row refreshes and entered text become blank.

In othere word the page refresh after adding each row and i want to avoid this.

Hope i explain well and need more i will tell.

below my code

Thanks