protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        //判断是否是编辑行
        if ((e.Row.RowState & DataControlRowState.Edit) != 0)
        {
            //在这里找你的文本框
        }
    }
}