FilteredBindingList and paging

colema18 posted on Wednesday, March 14, 2007

I have custom paging for a datagrid control that is binding to a BulletinList :
    ReadOnlyListBase<BulletinList, BulletinInfo> collection.

The 2.1 handbook refers to implementing paging, but it is more focused on only returning the rows JIT from the database. I however already have the fully populated BulletinList (under 200 rows) and my datagrid is only showing 10 rows at a time. This seemed to plug in just fine with the standard paging of the datagrid, but when I am trying to do custom navigation controls it is always displaying the 1st 10 records, no matter what currentpageindex is being set on the grid.

Can someone look at the snippets below and give me some ideas:

SearchResults.ascx
...
<asp:datagrid id="dgSearchResults" runat="server" BorderColor="#CCCCCC" BorderWidth="1px" CellPadding="0"
         HorizontalAlign="Center" Width="100%" AllowPaging="True" AllowSorting="True" AutoGenerateColumns="False"
         DataKeyField="" BorderStyle="Solid" AllowCustomPaging="True" PagerStyle-Visible="False" PageSize="4" >
        <AlternatingItemStyle HorizontalAlign="Left" CssClass="resultsTableEvenItemNoBorder"></AlternatingItemStyle>
        <ItemStyle HorizontalAlign="Left" CssClass="resultsTableOddItemNoBorder"></ItemStyle>
        <HeaderStyle HorizontalAlign="Left"   CssClass="resultsTableHeaderNoBorder" VerticalAlign="Middle"></HeaderStyle>
        <Columns>

    <asp:TemplateColumn HeaderStyle-HorizontalAlign ="Left" HeaderText = "<%$Resources:cde, resSlct %>" ItemStyle-Width="12px">
        <ItemTemplate >
        <asp:HyperLink id="lnkGo" runat="server" ImageUrl="../Images/view.gif" NavigateUrl='http://dev.vwcredit.com/dealers/applications/bulletins/PDFs/<%# DataBinder.Eval(Container.DataItem, "EncryptedPdfLink")%>' />
        </ItemTemplate>
   </asp:TemplateColumn>
   <asp:TemplateColumn HeaderStyle-HorizontalAlign ="Left" SortExpression="Number" HeaderText = "<%$Resources:FinanceSource, resBulletin %>" >
         <ItemTemplate >
            <asp:Label runat="server" ID= "lblBulletin" Text ='<%# DataBinder.Eval(Container.DataItem, "Number") %>' ></asp:Label>
         </ItemTemplate >
    </asp:TemplateColumn>
    <asp:TemplateColumn HeaderStyle-HorizontalAlign ="Left" SortExpression="Title" HeaderText="<%$Resources:FinanceSource, resTitle %>">
        <ItemTemplate >
            <asp:Label runat="server" ID= "lblTitle" Text ='<%# DataBinder.Eval(Container.DataItem, "Title") %>' ></asp:Label>
        </ItemTemplate >
    </asp:TemplateColumn>
    <asp:TemplateColumn HeaderStyle-HorizontalAlign ="Left" SortExpression="Comments" HeaderText="<%$Resources:cde, resComments%>">
        <ItemTemplate >
            <asp:Label runat="server" ID= "lblComments" Text ='<%# DataBinder.Eval(Container.DataItem, "Comments") %>' ></asp:Label>
        </ItemTemplate >
    </asp:TemplateColumn>
      </Columns>
    </asp:datagrid>

    <table width="100%">
    <tr>
        <td>Page
            <asp:Label ID="lblCurrentPage" runat="server" Text="1"></asp:Label>
            of
            <asp:Label ID="lblTotalPages" runat="server" Text="2"></asp:Label></td>
        <td align="right">Result Pages:
            <asp:LinkButton ID="lbtnPrevious" runat="server" CausesValidation="False" CommandArgument="Previous"
                CommandName="SetPage" OnClick="PageNav_Click"><<Prev</asp:LinkButton>
            <asp:PlaceHolder ID="phPages" runat="server"></asp:PlaceHolder>
            <asp:LinkButton ID="lbtnNext" runat="server" CausesValidation="False" CommandArgument="Next"
                CommandName="SetPage" OnClick="PageNav_Click">Next>></asp:LinkButton></td>
    </tr>
    </table>
...

SearchResults.ascx
...
protected void Page_Load(object sender, EventArgs e)
    {
        Session["days"] = "30";
        BulletinList bulletins;
        if (Session[key] != null)
        {
            bulletins = (BulletinList)Session[key];
        }
        else
        {
            bulletins = BulletinList.GetBulletinList(_dealerNumber);
            Session[key] = bulletins;
        }

        if (bulletins.Count != 0)
        {
            filteredBulletins = new FilteredBindingList<BulletinInfo>(bulletins);
            filteredBulletins.ApplyFilter("Language", Page.UICulture);
            if (Session["SortBy"] != null)
            {
                SortedBindingList<BulletinInfo> sortedBulletins = new SortedBindingList<BulletinInfo>(filteredBulletins);
                sortedBulletins.ApplySort((string)Session["SortBy"], (ListSortDirection)Session["SortByOrder"]);
                dgSearchResults.DataSource = sortedBulletins;
            }
            else
            {
                dgSearchResults.DataSource = filteredBulletins;
            }
        }
        if (!IsPostBack)
        {
            if (bulletins.Count != 0)
            {
                string ModifiedDaysRows;
                ModifiedDaysRows = Resources.FinanceSource.resBulletinResult.Replace("[rows]", bulletins.Count.ToString());
                lblText.Text = ModifiedDaysRows.Replace("[days]", Session["days"].ToString());
                dgSearchResults.VirtualItemCount = filteredBulletins.Count;
                BindGrid();
            }
            else
            {
                lblText.Text = Resources.FinanceSource.resNoSearchResults;
                dgSearchResults.Visible = false;
            }
        }
    }

---

    protected void BindGrid()
    {
        dgSearchResults.DataSource = filteredBulletins;
        dgSearchResults.DataBind();
    }

...

    protected void PageNav_Click(object sender, EventArgs e)
    {
        LinkButton lb = (LinkButton)sender;
        switch (lb.CommandArgument)
        {
            case "Previous":
                currentPage = dgSearchResults.CurrentPageIndex - 1;
                break;
            case "Next":
                currentPage = dgSearchResults.CurrentPageIndex + 1;
                break;
            default:
                currentPage = int.Parse(lb.CommandArgument) - 1;
                break;
        }
        dgSearchResults.CurrentPageIndex = currentPage;

        dgSearchResults.DataBind();
    }

RockfordLhotka replied on Thursday, March 15, 2007

If you already have the entire list in memory, then you need to take a different approach from what's shown in the book.

Data binding will raise the SelectObject event each time it needs a page. And that's where your options begin. You can either

Do the paging in the SelectObject event handler
Do the paging in your factory method
Do the paging in your DataPortal_Fetch method
Do the paging in your stored procedure

In your case only 1 and 2 are options, because those are the only options that run on the client (or web server) in all cases.

You'll need to create a list object that only contains the requested page of data. In 2.1.3+ the paging data comes to you in the EventArgs parameter passed to the SelectObject event handler. The solution is like this (pseudocode, I don't remember all the property names from the args):

CustomerList source = // get your complete data list
List<Customer> result = new List<Customer>();
int position;
foreach (Customer item in source)
{
if (position >= e.StartRow)
result.Add(item);
if (position > e.StartRow + e.PageSize)
break; // exit loop, we're done
position++;
}
return result;

That assumes you put the code in the factory method. You could just as easily put it in the SelectObject event handler.

FilteredBindingList and paging

colema18 posted on Wednesday, March 14, 2007

somayajulu replied on Thursday, March 15, 2007

RockfordLhotka replied on Thursday, March 15, 2007

mongo replied on Saturday, April 14, 2007