When you try to check for the Edit mode in the OnRowDataBound event of the GridView, you will face a problem when you try to edit the alternate row and checking for edit mode.
In the BindDetailsForEditMode event, you can check for following condition to ensure that you are into edit mode irrespective of normal row or alternate row you are editing.
if (e.Row.RowState == DataControlRowState.Edit || e.Row.RowState ==
(DataControlRowState.Edit | DataControlRowState.Alternate))
// write your statement that you want to fire in Edit mode