Realization of Gridview automatic sorting function

Two points to note:
1. To set the AllowSorting attribute of gridview to true, set the OnSorting event

2. Set the SortExpression attribute on the sorted columns in the OnSorting event

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                if (Session["Admin"] != "admin")
                {
                    // If the session expires, you should log in again 
                    this.Response.Write(" <script language=javascript>alert(' You do not have access to this page, please contact the administrator! ');window.location.href='../UserLogin.aspx';</script> ");
                }

                ViewState["sortExpression"] = "Isdistribution";
                ViewState["sort"] = " ASC";
            }
            // The binding information 
            BindNodeInfo();
        }

        public void BindNodeInfo()
        {
            NodeLogic log = new NodeLogic();
            DataSet myset = log.GetNodeInfo();     // Get data source 
            DataView myview = myset.Tables[0].DefaultView;
            myview.Sort = ViewState["sortExpression"].ToString() +" "+ ViewState["sort"].ToString();
            this.NodeGridView.DataSource = myview;
            NodeGridView.DataKeyNames = new string[] { "node_id" };               // Set the primary key field 
            NodeGridView.DataBind();                                                  // The binding GridView controls   
        }
        protected void NodeGridView_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            this.NodeGridView.PageIndex = e.NewPageIndex;
            BindNodeInfo();
        }
        protected void NodeGridView_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            //  Automatically to the first 1 Column number 
            if (e.Row.RowIndex > -1)
            {
                e.Row.Cells[0].Text = Convert.ToString(e.Row.RowIndex + 1);
            }
        }
        protected void NodeGridView_RowDeleting(object sender, GridViewDeleteEventArgs e)
        {
            NodeLogic log = new NodeLogic();
            int id = int.Parse(this.NodeGridView.DataKeys[e.RowIndex].Values[0].ToString());
            if (log.DeleteNodeInfo(id))
            {
                this.Page.ClientScript.RegisterStartupScript(this.GetType(), "", "alert(' Delete successful! ');", true);
            }
            else
                this.Page.ClientScript.RegisterStartupScript(this.GetType(), "", "alert(' Delete failed! ');", true);
            // Re-update the data display 
            BindNodeInfo();
        }
        protected void NodemGridView_RowEditing(object sender, GridViewEditEventArgs e)
        {
        }
        protected void AddNode_Click(object sender, EventArgs e)
        {
            Response.Redirect("AddNode.aspx");
        }
        protected void NodeGridView_Sorting(object sender, GridViewSortEventArgs e)
        {
            if (ViewState["sortExpression"] != null)
            {
                if (ViewState["sort"].ToString() == "Asc")
                {
                    ViewState["sort"] = "Desc";
                }
                else
                {
                    ViewState["sort"] = "Asc";

                }
            }
            BindNodeInfo();
        }