สอบถามปัญหาค่ะ linkbutton ใน data gridview ไม่ทำงาน

protected void Page_Init(object sender, EventArgs e)
        {
            GridView1.DataBind();
        }

        protected void GridView1_DataBound(object sender, EventArgs e)
        {
            foreach (GridViewRow row in GridView1.Rows)
            {
                if (row.RowType == DataControlRowType.DataRow)
                {
                    LinkButton lb = new LinkButton();
                    lb.Text = "Approve";
                    lb.CommandName = "ApproveVacation";
                    lb.Command += LinkButton_Command;
                    row.Cells[0].Controls.Add(lb);
                }
            }
        }

        protected void LinkButton_Command(object sender, CommandEventArgs e)
        {
            if (e.CommandName == "ApproveVacation")
            {

            }
        }