if (!GridView1.Rows[GridView1.CurrentCell.RowIndex].IsNewRow)
{
foreach (DataGridViewCell cell in GridView1.Rows[GridView1.CurrentCell.RowIndex].Cells)
{
//here you must test for all and then return only if it is false
if (cell.Value == System.DBNull.Value)
{
return false;
}
}
}