Need help to create a unique id

I got a gridview with some checboxes, and I've found a way to hold the selected rows even if I change page. I'm using this to create a unique id for each row.
Here is a part of it:

if (checkbox.Checked)
        {
            ViewState[GridView1.UniqueID] = true;
        }
        else
        {
            ViewState.Remove(GridView1.UniqueID);
        }
 I wonder what I should set as ViewState. Now I got GridView1.UniqueID, but I need something that is unique for each row, like the id from the database or something. How can I get the value in there? In the ViewState[## IN HERE ##]?
Thanks for any help!

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