At your aspx.cs try below code:
foreach (GridViewRow gridrow in GridView1.Rows)
{
CheckBox cb = (CheckBox)gridrow.FindControl("MovieSelector");
if (cb != null && cb.Checked)
{
string obj = gridrow.Cells[2].Text;
totalId = totalId + ","+ obj;
}
}
this was you can work on every row for which check box is checkedand can update database with required details.
gridrow.Cells[] gives you the value of corresponding column in gridview.
Hope this helped !
Regards,
Divya