Disappearing GridView - Newsgroup???

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 EnableSortingAn dPageCallbacks parameter from the script
below and add a PageIndexChangi ng 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 EnableSortingAn dPageCallbacks is
enabled.
Protected Sub AuthorsGridView _PageIndexChang ing(ByVal sender As Object,
ByVal e As System.Web.UI.W ebControls.Grid ViewPageEventAr gs) Handles
AuthorsGridView .PageIndexChang ing

AuthorsGridView .PageIndex = e.NewPageIndex

bindDataToGridV iew()

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 bindDataToGridV iew()
'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.Sql Client.SqlConne ction("server=l ocalhost;databa se=pubs;integra ted
security=SSPI")
Dim cmd = New System.Data.Sql Client.SqlComma nd(strSQL, con)
Dim ad As New System.Data.Sql Client.SqlDataA dapter(cmd)

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

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

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

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

</script>

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

<h3>Disappearin g GridView Example</h3>

<asp:gridview id="AuthorsGrid View"
autogeneratecol umns="False"
AllowPaging="Tr ue"
EnableSortingAn dPagingCallback s="True"
PageSize="3"
runat="server" CellPadding="4" ForeColor="#333 333" GridLines="None ">
<Columns>
<asp:BoundFie ld DataField="au_f name" HeaderText="Fir st Name">
</asp:BoundField>
<asp:BoundFie ld DataField="au_l name" HeaderText="Las t Name">
</asp:BoundField>
<asp:BoundFie ld DataField="City " HeaderText="Cit y">
</asp:BoundField>
</Columns>
<RowStyle BackColor="#E3E AEB" />
<PagerStyle BackColor="#666 666" ForeColor="Whit e"
HorizontalAlign ="Center" />
<HeaderStyle BackColor="#1C5 E55" Font-Bold="True"
ForeColor="Whit e" />
<AlternatingRow Style BackColor="Whit e" />
</asp:gridview>
</form>
</body>
</html>

Apr 16 '07 #1

Subscribe Reply

2716

marss

Don Miller wrote:

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?

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 PageIndexChangi ng event, it
is not raised.

<asp:GridView ID="AuthorsGrid View" runat="server" AllowPaging="Tr ue"
EnableSortingAn dPagingCallback s="True" PageSize="3">
......
</asp:GridView>

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

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

Regards

Apr 16 '07 #2

Don Miller

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_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
GridViewSQLData Source.SelectCo mmand = "SELECT [au_fname],
[au_lname], [city] FROM [authors] WHERE [city] = 'Oakland'"
End Sub

Protected Sub LinkButton2_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
GridViewSQLData Source.SelectCo mmand = "SELECT [au_fname],
[au_lname], [city] FROM [authors]"
End Sub
</script>

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

<h3>Disappearin g GridViews</h3>

<asp:LinkButt on ID="LinkButton1 " runat="server"
OnClick="LinkBu tton1_Click">Oa kland Only</asp:LinkButton>
<asp:LinkButt on ID="LinkButton2 " runat="server"
OnClick="LinkBu tton2_Click">Al l Cities</asp:LinkButton>

<asp:gridview id="AuthorsGrid View"
autogeneratecol umns="False"
AllowPaging="Tr ue"
EnableSortingAn dPagingCallback s="True"
PageSize="3"
DataSourceID = "GridViewSQLDat aSource"
runat="server" CellPadding="4" ForeColor="#333 333" GridLines="None ">
<Columns>
<asp:BoundFie ld DataField="au_f name" HeaderText="Fir st Name">
</asp:BoundField>
<asp:BoundFie ld DataField="au_l name" HeaderText="Las t Name">
</asp:BoundField>
<asp:BoundFie ld DataField="City " HeaderText="Cit y">
</asp:BoundField>
</Columns>
<RowStyle BackColor="#E3E AEB" />
<PagerStyle BackColor="#666 666" ForeColor="Whit e"
HorizontalAlign ="Center" />
<HeaderStyle BackColor="#1C5 E55" Font-Bold="True"
ForeColor="Whit e" />
<AlternatingRow Style BackColor="Whit e" />
</asp:gridview>

<asp:SqlDataSou rce ID="GridViewSQL DataSource"
ConnectionStrin g="server=local host;database=p ubs;integrated
security=SSPI"
runat="server">
</asp:SqlDataSour ce>

</form>
</body>
</html>

Apr 16 '07 #3

marss

Don Miller wrote:

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)

Save the chosen select command text in the ViewState and assign it to
GridViewSQLData Source.SelectCo mmand in the page load event handler.
Example:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As
System.EventArg s) Handles Me.Load
If (IsCallback) Then
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
End If
End Sub

Protected Sub LinkButton1_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
Me.SelectComman d = "SELECT .... "
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
End Sub

Protected Sub LinkButton2_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
Me.SelectComman d = "SELECT ...."
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
End Sub

Private Property SelectCommand() As String
Get
Return ViewState("Sele ctCommand").ToS tring()
End Get
Set(ByVal value As String)
ViewState("Sele ctCommand") = value
End Set
End Property

Regards

Apr 17 '07 #4

Don Miller

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_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
Me.SelectComman d = "SELECT [au_fname], [au_lname], [city] FROM
[authors] WHERE [city] = 'Oakland'"
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
AuthorsGridView .PageIndex = 0
End Sub

"marss" <ma******@gmail .comwrote in message
news:11******** *************@y 80g2000hsf.goog legroups.com...

>
Don Miller wrote:
>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)

Save the chosen select command text in the ViewState and assign it to
GridViewSQLData Source.SelectCo mmand in the page load event handler.
Example:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As
System.EventArg s) Handles Me.Load
If (IsCallback) Then
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
End If
End Sub

Protected Sub LinkButton1_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
Me.SelectComman d = "SELECT .... "
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
End Sub

Protected Sub LinkButton2_Cli ck(ByVal sender As Object, ByVal e As
System.EventArg s)
Me.SelectComman d = "SELECT ...."
GridViewSQLData Source.SelectCo mmand = Me.SelectComman d
End Sub

Private Property SelectCommand() As String
Get
Return ViewState("Sele ctCommand").ToS tring()
End Get
Set(ByVal value As String)
ViewState("Sele ctCommand") = value
End Set
End Property

Regards

Apr 17 '07 #5

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