保持DropDownList选择的值与GridView中显示的值相同

I am using a ListView to show the table. I change one of the field in the to a dropdownlist so that when I click on "Edit" button, that field will be a dropdown with all the values already populate in it. My problem is that when I click on the "Edit" the dropdownlist's selected value will change to the first value of the dropdown rather than the previous value that shows in the ListView. How could I control this to make the selected value same as the one showed originally. Thanks. I would be happy to make any clarifications if the question is not clear.I am using a ListView to show the table. I chan