display warning message if dropdownbox is checked even when the values in grid view changed but not saved

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C#

C#4.0

hi,
i have a drop down box, which retrieves data from database and displays in gridview...
i have 4 columns in gridview in which 2 columns are duplicate.

ex:
C1 C2 D1 D2
1   4  1   4
5   6  5   6



i took extra duplicate columns for reference and those columns are kept hidden..

here when i changed any of the values in column1 and column2 but not saved(doesn't click on save button)
and i changed the selection in drop down box.. the it should display an warning message that values are changed but not saved....


can you please help in this code..