Question

i want to do sorting in the listview from code behind, and i have done it by below code:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
        BindLV("");
}

public DataTable GetEmployee(string query)
{
    SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString);
    SqlDataAdapter ada = new SqlDataAdapter(query, con);
    DataTable dtEmp = new DataTable();
    ada.Fill(dtEmp);
    return dtEmp;
}

private void BindLV(string SortExpression)
{
    string UpdateQuery = "Select * from Employee" + SortExpression;
    SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString);

    lvEmployee.DataSource = GetEmployee(UpdateQuery);
    lvEmployee.DataBind();
}

protected void lvEmployee_Sorting(object sender, ListViewSortEventArgs e)
{
    ImageButton imEmpID = lvEmployee.FindControl("imEmpID") as ImageButton;
    ImageButton imEmpName = lvEmployee.FindControl("imEmpName") as ImageButton;

    string DefaultSortIMG = "~/img/asc.png";
    string imgUrl = "~/img/desc.png";

    if (ViewState["SortExpression"] != null)
    {
        if (ViewState["SortExpression"].ToString() == e.SortExpression)
        {
            ViewState["SortExpression"] = null;
            imgUrl = DefaultSortIMG;
        }
        else
        {
            ViewState["SortExpression"] = e.SortExpression;
        }
    }
    else
    {
        ViewState["SortExpression"] = e.SortExpression;
    }

    switch (e.SortExpression)
    {
        case "EmpID":
            if (imEmpName != null)
                imEmpName.ImageUrl = DefaultSortIMG;

            if (imEmpID != null)
                imEmpID.ImageUrl = imgUrl;

            break;

        case "EmpName":

            if (imEmpID != null)
                imEmpID.ImageUrl = DefaultSortIMG;

            if (imEmpName != null)
                imEmpName.ImageUrl = imgUrl;

            break;
    }
    BindLV(" order by " + e.SortExpression + " " + ((ViewState["SortExpression"] != null) ? "ASC" : "DESC"));
}

but the problem is i’m using another function for data paging as below in code behind which is contain of sorting as well:

 protected void DataPager1_PreRender(object sender, EventArgs e)
{
    lvEmployee.DataSource = GetEmployee("Select * from Employee");
    lvEmployee.DataBind();

}

and my data pager code which is located at LayoutTemplate in .aspx page:

<asp:DataPager ID="DataPager1" runat="server" PagedControlID="lvEmployee" PageSize="5" onprerender="DataPager1_PreRender">
                <Fields>
                    <asp:NextPreviousPagerField ButtonType="Button" ShowFirstPageButton="true" ShowLastPageButton="true"/>
                </Fields>
            </asp:DataPager>

Every time i click at the name to sort it, there will be no change in the list. E have traced the problem, and I have found out that the sorting function is working properly. But before the page come up, the DataPager1_PreRender function is called and again shows the list without sorting.

Could you please guide me how to do sorting and dataPaging together without this problem. Appreciate your consideration.

Answer 1

I have over come to this problem by using Session.
before i use session i found out every time i press the next page or anytime the page refresh it will execute the DataPager1_PreRender() and i have set the data source to

GetEmployee("Select * from Employee");

that’s why the sorting never happens.
i have add Session["UpdateQT"] = UpdateQuery; to BindLV() to keep the update query and i have change the DataPager1_PreRender() to

string strtmp = Session["UpdateQT"].ToString();
    if (strtmp == null) 
    {
        strtmp = "Select * from Employee";
    }

    lvEmployee.DataSource = GetEmployee(strtmp);
    lvEmployee.DataBind();

to keep the latest query after sorting.
i hope it helps somebody.