how to get the data from unigrid using id and get rows data

Hi, I tried to update the products data using csv file, I am binding my csv file to unigrid using dataset and i need to get the data from the unigrid to update the data on button click, so i created a method and tried to retrieve the data from the unigrid using GridViewRow row in bulkGridProductsdata.GridView.Row ) but i am getting null value from it, is there any specific format to get the data from the unigrid.