Disappearing GridView - Newsgroup???

  • Thread starter Thread starter Don Miller
  • Start date Start date
D

Don Miller

This is a repost of a reproducible problem/bug with GridView with dynamic
SQL and binding. Is there a better ASP.NET newsgroup I should post to where
MS techs or MVPs take an interest in such problems?

Thanks.


Here is an example of what I believe is a bug in ASP.NET 2.0 GridView paging
without postbacks (or at least not documented how to fix it). Once the
GridView is displayed, clicking on any of the paging tools causes the
GridView to completely disappear! This happens when either DataSets or
DataTables are used (it doesn't work at all for DataReaders because they
don't support paging apparently).

If you remove the EnableSortingAndPageCallbacks parameter from the script
below and add a PageIndexChanging sub, the paging works fine except there is
a postback for every page. I would prefer to NOT have a postback and instead
use the the AJAX-like callbacks when EnableSortingAndPageCallbacks is
enabled.
Protected Sub AuthorsGridView_PageIndexChanging(ByVal sender As Object,
ByVal e As System.Web.UI.WebControls.GridViewPageEventArgs) Handles
AuthorsGridView.PageIndexChanging

AuthorsGridView.PageIndex = e.NewPageIndex

bindDataToGridView()

End Sub

So, how can you use GridView with callback paging without postbacks? What's
missing from the code and why shouldn't the code work? And where is the
documentation for avoiding this problem?

Thanks for any help.

<%@ Page language="VB" %>

<script runat="server">

Private Sub bindDataToGridView()
'This example uses Microsoft SQL Server and connects
Dim strSQL As String = "SELECT [au_fname], [au_lname], [city] FROM
[authors]"
Dim con As New
System.Data.SqlClient.SqlConnection("server=localhost;database=pubs;integrated
security=SSPI")
Dim cmd = New System.Data.SqlClient.SqlCommand(strSQL, con)
Dim ad As New System.Data.SqlClient.SqlDataAdapter(cmd)

Dim ds As New Data.DataSet
'Dim dt As New Data.DataTable

ad.Fill(ds)
'ad.Fill(dt)

AuthorsGridView.DataSource = ds
'AuthorsGridView.DataSource = dt
AuthorsGridView.DataBind()
End Sub

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
If Not IsPostBack Then
bindDataToGridView()
End If
End Sub

</script>

<html>
<body>
<form id="Form1" runat="server">

<h3>Disappearing GridView Example</h3>

<asp:gridview id="AuthorsGridView"
autogeneratecolumns="False"
AllowPaging="True"
EnableSortingAndPagingCallbacks="True"
PageSize="3"
runat="server" CellPadding="4" ForeColor="#333333" GridLines="None">
<Columns>
<asp:BoundField DataField="au_fname" HeaderText="First Name">
</asp:BoundField>
<asp:BoundField DataField="au_lname" HeaderText="Last Name">
</asp:BoundField>
<asp:BoundField DataField="City" HeaderText="City">
</asp:BoundField>
</Columns>
<RowStyle BackColor="#E3EAEB" />
<PagerStyle BackColor="#666666" ForeColor="White"
HorizontalAlign="Center" />
<HeaderStyle BackColor="#1C5E55" Font-Bold="True"
ForeColor="White" />
<AlternatingRowStyle BackColor="White" />
</asp:gridview>
</form>
</body>
</html>
 
Don said:
So, how can you use GridView with callback paging without postbacks? What's
missing from the code and why shouldn't the code work? And where is the
documentation for avoiding this problem?
Click to expand...

Hi,
The GridView disappers because it is empty. If you want to use a
callback to change the page set GridView's datasource in the page load
event handler. You don't need to process PageIndexChanging event, it
is not raised.

<asp:GridView ID="AuthorsGridView" runat="server" AllowPaging="True"
EnableSortingAndPagingCallbacks="True" PageSize="3">
......
</asp:GridView>

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
If Not IsPostBack Then
bindDataToGridView()
End If

If Not IsCallback Then
......
AuthorsGridView.DataSource = ds
'AuthorsGridView.DataBind() Don't bind here!
End If
End Sub

Regards
 
Thanks very much for the reply. What I'm really trying to do is to
dynamically change the GridView by changing (on command) the SELECT
statement for the GridView. Initially, the GridView is empty until a command
is chosen (with a hyperlink button). In the actual application the GridView
is only one of several on a page that are hidden by changing Views. I would
like to do this (AJAX paging) with a SQL datasource by dynamically changing
the SELECT statement but I run into the same disappearing GridView when I
tried that (see example below)

I appreciate your help and I obviously don't understand how these things
work but I've already spent hours of reading and trial and error and seem no
closer. Thanks again.

<%@ Page language="VB" %>

<script runat="server">

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

End Sub

Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As
System.EventArgs)
GridViewSQLDataSource.SelectCommand = "SELECT [au_fname],
[au_lname], [city] FROM [authors] WHERE [city] = 'Oakland'"
End Sub

Protected Sub LinkButton2_Click(ByVal sender As Object, ByVal e As
System.EventArgs)
GridViewSQLDataSource.SelectCommand = "SELECT [au_fname],
[au_lname], [city] FROM [authors]"
End Sub
</script>

<html>
<body>
<form id="Form1" runat="server">

<h3>Disappearing GridViews</h3>

<asp:LinkButton ID="LinkButton1" runat="server"
OnClick="LinkButton1_Click">Oakland Only</asp:LinkButton>
<asp:LinkButton ID="LinkButton2" runat="server"
OnClick="LinkButton2_Click">All Cities</asp:LinkButton>

<asp:gridview id="AuthorsGridView"
autogeneratecolumns="False"
AllowPaging="True"
EnableSortingAndPagingCallbacks="True"
PageSize="3"
DataSourceID = "GridViewSQLDataSource"
runat="server" CellPadding="4" ForeColor="#333333" GridLines="None">
<Columns>
<asp:BoundField DataField="au_fname" HeaderText="First Name">
</asp:BoundField>
<asp:BoundField DataField="au_lname" HeaderText="Last Name">
</asp:BoundField>
<asp:BoundField DataField="City" HeaderText="City">
</asp:BoundField>
</Columns>
<RowStyle BackColor="#E3EAEB" />
<PagerStyle BackColor="#666666" ForeColor="White"
HorizontalAlign="Center" />
<HeaderStyle BackColor="#1C5E55" Font-Bold="True"
ForeColor="White" />
<AlternatingRowStyle BackColor="White" />
</asp:gridview>

<asp:SqlDataSource ID="GridViewSQLDataSource"
ConnectionString="server=localhost;database=pubs;integrated
security=SSPI"
runat="server">
</asp:SqlDataSource>

</form>
</body>
</html>
 
Don said:
Thanks very much for the reply. What I'm really trying to do is to
dynamically change the GridView by changing (on command) the SELECT
statement for the GridView. Initially, the GridView is empty until a command
is chosen (with a hyperlink button). In the actual application the GridView
is only one of several on a page that are hidden by changing Views. I would
like to do this (AJAX paging) with a SQL datasource by dynamically changing
the SELECT statement but I run into the same disappearing GridView when I
tried that (see example below)
Click to expand...


Save the chosen select command text in the ViewState and assign it to
GridViewSQLDataSource.SelectCommand in the page load event handler.
Example:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Me.Load
If (IsCallback) Then
GridViewSQLDataSource.SelectCommand = Me.SelectCommand
End If
End Sub

Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As
System.EventArgs)
Me.SelectCommand = "SELECT .... "
GridViewSQLDataSource.SelectCommand = Me.SelectCommand
End Sub

Protected Sub LinkButton2_Click(ByVal sender As Object, ByVal e As
System.EventArgs)
Me.SelectCommand = "SELECT ...."
GridViewSQLDataSource.SelectCommand = Me.SelectCommand
End Sub

Private Property SelectCommand() As String
Get
Return ViewState("SelectCommand").ToString()
End Get
Set(ByVal value As String)
ViewState("SelectCommand") = value
End Set
End Property

Regards
 
Thank you so much! I'm still learning and quite sure I wouldn't have come up
that solution using ViewState or even know where to place the code in the
Event cascade (onLoad, onCallback, GridView init/load, etc.).

It still seems like a bug to me that the SELECT command for the DataSource
has to be reset again with a Callback. It is set for the GridView each time
a link button was pressed and it seems like that should be enough. Why
should a dynamic SELECT statement assigned to a DataSource get trashed on a
Callback? This solution (thanks again) seems like a hack to get around this
unexpected behavior. I mean, why should anyone expect that you have to do
this?

Anyway, I did find I had to add one line of code to reset the PageIndex back
to 0 when a new SELECT is displayed to keep the Pages straight.

Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As
System.EventArgs)
Me.SelectCommand = "SELECT [au_fname], [au_lname], [city] FROM
[authors] WHERE [city] = 'Oakland'"
GridViewSQLDataSource.SelectCommand = Me.SelectCommand
AuthorsGridView.PageIndex = 0
End Sub
 
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