Linq paging Question

barakros · January 27th, 2010, 06:39 AM

hi
I created a simple page with dropdownlist which holds categories of items
- category 1

also I have a tree view of category 2 of items

also I placed a grid view on the page with no datasource associated with it.

when the dropdownlist selected index change I run a linq code to select the items where category1== the selected dropdownlist value and bind the results to the grid

when the tree view selected node change I run a linq code to select the items where category2==the selected treenode value and bind the results to the grid

thats works fine until I start paging - I get empty data when going to the next page (which we know has data since the grid pager show page 2,3...)

why is that?
does the linq code is good just for the first bind and after that I need to handle the paging myself in code?

TIA
BARAK

Imar · January 27th, 2010, 09:42 AM

Maybe the new data overwrites the current state? Difficult to say without seeing any code.

Can you post the full, working code for this page?

Imar

barakros · January 27th, 2010, 10:44 AM

thanks
I post the code:
I created linq dbml with some tables
the main of them is items from where I take the data for the grid

the init function are not so important - they just put the data in the treeview and dropdownlist in the first time the page is load
so we have the filters GUI objects.

ASPX:

Code:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title></title>
</head>
<body>
  <form id="form1" runat="server">
  <div>
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
      <ContentTemplate>
        <table width="100">
          <tr valign="top">
            <td width="20%">
              
              <asp:DropDownList ID="DropDownList1" runat="server" 
                AppendDataBoundItems="True" 
                AutoPostBack="True">
                <asp:ListItem Value="0">Select Designer:</asp:ListItem>
              </asp:DropDownList>
              
              <asp:TreeView ID="TreeView1" runat="server" ImageSet="Arrows">
                <ParentNodeStyle Font-Bold="True" />
                <HoverNodeStyle Font-Underline="True" ForeColor="#6D266A" />
                <SelectedNodeStyle Font-Underline="True" ForeColor="#6D266A" 
                 HorizontalPadding="0px"
                  VerticalPadding="0px" />
                <NodeStyle Font-Names="Tahoma" Font-Size="10pt" 
                ForeColor="#6D266A" HorizontalPadding="5px"
                  NodeSpacing="0px" VerticalPadding="0px" />
              </asp:TreeView>
            </td>
            <td width="80%">
              <asp:GridView ID="GridView1" runat="server"
               AllowPaging="True" AutoGenerateColumns="False" 
               DataKeyNames="item" >
                <Columns>
                  <asp:BoundField DataField="item" HeaderText="Item" ReadOnly="True" 
                    SortExpression="item" />
                  <asp:BoundField DataField="itemdesc" HeaderText="Description" 
                    SortExpression="itemdesc" />
                 </Columns>
              </asp:GridView>              
            </td>
          </tr>
        </table>
        </ContentTemplate>        
    </asp:UpdatePanel>
  </div>
  </form>
</body>
</html>

code behind (VB.NET):

Code:

Partial Class _Default
  Inherits System.Web.UI.Page

  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If Not Page.IsPostBack Then
      Using mydata As New TreeTestDataContext()
        InitItemClassTree(mydata)
        InitDesigners(mydata)
      End Using
    End If
  End Sub
  Private Sub InitDesigners(ByRef aDataContext As TreeTestDataContext)
    Dim allDesigners = From d In aDataContext.designers _
                      Order By d.designer _
                      Select New With {d.id, d.designer}

    For Each d In allDesigners
      Dim newListItem As New ListItem
      newListItem.Value = d.id
      newListItem.Text = d.designer
      DropDownList1.Items.Add(newListItem)
    Next
  End Sub
  Private Sub InitItemClassTree(ByRef aDataContext As TreeTestDataContext)
    Dim allclasses = From c In aDataContext.itemclassesgroups _
                     Order By c.forder _
                     Select New With {c.id, c.name, c.itemclasses}

    For Each c In allclasses
      Dim newExpandNode As New TreeNode
      With newExpandNode
        .Text = c.name
        .Value = c.id
        .SelectAction = TreeNodeSelectAction.Expand
        .Expanded = False
        For Each i As itemclass In c.itemclasses
          Dim newSelectNode As New TreeNode
          With newSelectNode
            .SelectAction = TreeNodeSelectAction.Select
            .Text = i.itemclass
            .Value = i.id
          End With
          newExpandNode.ChildNodes.Add(newSelectNode)
        Next
      End With
      TreeView1.Nodes.Add(newExpandNode)
    Next
  End Sub

  Protected Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged
    Using mydata As New TreeTestDataContext
      Dim allItemsByDesignerId = From it In mydata.items _
                                  Where it.designerid = DropDownList1.SelectedValue _
                                  Order By it.sortorder _
                                  Select New With {it.item, it.itemdesc}
      GridView1.DataSource = allItemsByDesignerId
      GridView1.DataBind()
    End Using
  End Sub

  Protected Sub TreeView1_SelectedNodeChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles TreeView1.SelectedNodeChanged
    Using mydata As New TreeTestDataContext
      Dim allItemsByClassId = From it In mydata.items _
                                  Where it.itemclassid = TreeView1.SelectedValue _
                                  Order By it.sortorder _
                                  Select New With {it.item, it.itemdesc}
      GridView1.DataSource = allItemsByClassId
      GridView1.DataBind()
    End Using
  End Sub
End Class

the error I am getting when pressing on the paging links (2 3 ...)
is this:

Code:

Line: 4723
Error: Sys.WebForms.PageRequestManagerServerErrorException: The GridView 'GridView1' fired event PageIndexChanging which wasn't handled.

what handeling I need to do here? isn't it suppose to be auomatically?

Thanks very much
BARAK

Imar · January 27th, 2010, 11:48 AM

Nope; not when manually binding data. Take a look at this:

Code:

 
  If Not Page.IsPostBack Then
     Using mydata As New TreeTestDataContext()
       InitItemClassTree(mydata)
       InitDesigners(mydata)
     End Using
   End If

You only bind data when the page does't post back. The GridView doesn't maintain all its data in ViewState (otherwise it would create too much overhead, and defeat the purpose of paging) so the data is gone after a Postback.

You can use a LinqDataSource and let the controls handle it, or read a bit more about implementing custom paging scenarios: http://www.google.nl/search?hl=nl&q=...&meta=&aq=f&oq=

Cheers,

Imar