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Archive for the ‘Asp.Net’ Category

Handling multiple configuration settings (Development, Staging, Production) gracefully.

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In 2.0 multiple connectionStrings & appSettings can be handled very easily using the attribute “configSource”

create a new xml file devAppSettings.config under a new folder myConfigsettings

(continue reading…)

Written by gchandra

May 1, 2008 at 8:52 pm

Posted in Asp.Net, Web Coding

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AJAX – Export to Excel / Word

with 17 comments

If you are using Update Panel and try to Export gridview contents to EXCEL or Word, your page will throw nasty error. “Sys.WebForms.PageRequestManagerParserErrorException”

Its because AJAX & Response.write don’t go together.  By calling Response.Write() directly you are bypassing the normal rendering mechanism of ASP.NET controls. The bits you write are going straight out to the client without further processing (well, mostly…). This means that UpdatePanel can’t encode the data in its special format.

There are couple of ways to solve this problem.

1. Place the Export Button outside of Update Panel.

2. By Pass the Export Button using <Triggers>

            <asp:PostBackTrigger ControlID=”cmdExport” />

if your Export button is part of UserControl then specify usercontrolid:buttonid

            <asp:PostBackTrigger ControlID=”uscSelCtl:cmdExport” />

More Reading…

Written by gchandra

January 8, 2008 at 10:12 am Web Service Timing Out (0x80004005)

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Recently if your webservices started failing / timing out it its worth your time to take a look at this support article.

“HttpException (0x80004005): Request timed out.”

“System.InvalidOperationException: There were not enough free threads in the ThreadPool object to complete the operation”

 Contention, poor performance, and deadlocks when you make Web service requests from ASP.NET applications

Related Reading :

Item 5 talks about Asp.Net WS

Written by gchandra

January 8, 2008 at 9:47 am

Asp.Net Filter Datatable by Column

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Filter Datatable by Rows

If you need to get subset of a big dataset into datatable Rowwise …

Dim dtEmp as DataTable
Dim dsEmployee as New DataSet

dsEmployee = someobject.getdata()  'dataset can be populated in many ways which is not explained here.

Dim sExpr as String
Dim drRows() as DataRow, drSingleRow as DataRow

sExpr = "EmpID > 100"  'Condition

drRows = dsEmployee.Tables(0).Select(sExpr)

'If you need to add Sort Order it can be added to sExpr

Dim sSortOrder as String
sSortOrder = "EmpName DESC"
drRows = dsEmployee.Tables(0).Select(sExpr,sSortOrder)

For Each drSingleRow in drRows

' Datatable dtEmp has filtered records

Filter Datatable by Column

If you need to get subset of big dataset into datatable columnwise…

Dim dtEmp as DataTable
Dim dsEmployee as New DataSet

dsEmployoee = someobject.getdata()  'dataset can be populated in many ways which is not explained here.

'This copies the structure and data

dtEmp = dsEmployee.Tables(0).Copy

dtEmp.Columns.Remove("Unwanted Column 1")
dtEmp.Columns.Remove("Unwanted Column 2")
dtEmp.Columns.Remove("Unwanted Column 3")

Written by gchandra

January 7, 2008 at 4:13 pm

Prevent Session Timeout in

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Prevent Session Timeout in [VB]

ASP.Net 2.0 [VB]

Inspired by this article from Code Project. [Thanks Ach1lles ]

I slightly modified few things to work for VB and VS2005 environment. The code works perfect and I’m very happy with it.First I created a Module file and created this function.

Public Function KeepAlive() As String

        Dim int_MilliSecondsTimeOut As Integer = (HttpContext.Current.Session.Timeout * 60000) - 30000
        Dim sScript As New StringBuilder
        sScript.Append("<script type='text/javascript'>" & vbNewLine)
        'Number Of Reconnects
        sScript.Append("var count=0;" & vbNewLine)
        'Maximum reconnects Setting
        sScript.Append("var max = 6;" & vbNewLine)
        sScript.Append("function Reconnect(){" & vbNewLine)
        sScript.Append("count++;" & vbNewLine)
        sScript.Append("var d = new Date();" & vbNewLine)
        sScript.Append("var curr_hour = d.getHours();" & vbNewLine)
        sScript.Append("var curr_min = d.getMinutes();" & vbNewLine)
        sScript.Append("if (count < max){" & vbNewLine)
        sScript.Append("window.status = 'Refreshed ' + count.toString() + ' time(s) &#91;' + curr_hour + ':' + curr_min + '&#93;';" & vbNewLine)
        sScript.Append("var img = new Image(1,1);" & vbNewLine)
        sScript.Append("img.src = 'http://localhost/myapp/reconnect.aspx';" & vbNewLine)

        sScript.Append("}" & vbNewLine)
        sScript.Append("}" & vbNewLine)
        sScript.Append(int_MilliSecondsTimeOut.ToString() & "); //Set to length required" & vbNewLine)

        KeepAlive = sScript.ToString
End Function

All this code does is, build a simple javascript function and its called from server side.The works like this,- Gets the current session timeout duration.
– Subtract 30 seconds from it and assign it to MilliSecondsTimeOut variable
– Create a Reconnect() javascript function
– Create a global variable with max value 6
– Get current hour and Min [just for displaying the last refresh time]
– Verify whether count is less than max value (ie 6)
– If so, change the window status with Text
– Create a dummy image and set reconnect.aspx url as its source [this way a call is made to server and it wont session timeout]Create a timer using window.setInterval and assign the MilliSecondsTimeOut value.
[this way this function is called 30 seconds before session timeout]Tha max value (6) can be set to any number. If its 6 then this session timeout is avoided 5 times.

Default session timeout is 20min. 20 * 5 = 100 mins. Which is good for non-secure page.


On the pages where I want to prevent Session Timeout I entered this line.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
  'dont forget to add this line 
  Page.ClientScript.RegisterClientScriptBlock(Me.GetType, "reconn key", KeepAlive())
 If Not Page.IsPostBack Then
 End If

Catch eX as Exception
End Try
End Sub

Created reconnect.aspx in Visual Studio and deleted the .vb and .designer.vb files.This is the final version of reconnect.aspx

<%@ Page Language="vb" AutoEventWireup="false"%>
<%@ OutputCache Location="None" VaryByParam="None" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "<a href="" mce_href=""></a>">
<html xmlns="<a href="" mce_href=""></a>" >

Note : When you compile the project sometimes, VS2005 complains reconnect.aspx is not in right format.
So I EXCLUDED this file from my project. Now VS 2005 will compile without complaining and the logic will also work.- Happy Programming

Written by gchandra

November 26, 2007 at 3:42 pm

Copy Datatable from one Dataset to another Dataset

with 10 comments

 Copying a datatable from one dataset  to another was not that straightforward as I thought.

Dim dsSource As New DataSet
Dim dsDestination As New DataSet

'Your way to get data from XML or DB.
dsSource = object.getdata()

dsDestination = object.getmoredata()

'This is important, without this it will result in error
'when you try to copy the datatable from one dataset to another

dsSource.Tables(0).TableName = "NewTableName"


dsDestination.Tables(0).Tablename = "SomeTable"
dsDestination.Tables(1).Tablename = "NewTableName"   'The one we copied from other Dataset

Note 1 : When you are using more than one datatable in a dataset it is advisable you name the datatables.

Note 2 : These kinds of scenarios arise, when you are trying to establish Relation between datatables in a dataset.

(Cascading master – detail relation)

Written by gchandra

November 15, 2007 at 2:12 pm

Posted in Asp.Net, Web Coding

Tagged with , , ,

Creating dynamic, fancy EmptyDataText for GridView

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Gridview has capability to display “default” messages when “No data” exists during binding.

Standard Way in .aspx

<asp:GridView ID=”gvControl” runat=”server” AutoGenerateColumns=”False” GridLines=”None” CellPadding=”0″ CellSpacing=”0″ OnRowDataBound=”gvCategories_RowDataBound” BackColor=”#dddddd” ShowHeader=”false” EmptyDataText=”<BR> No data exists <BR><BR>“>

Fancy Way (.vb or .cs)

You can make it fancy & dynamic by doing it in code behind.


Create fancy texts using WordArt (MS Word) and copy it to Image Editor (, gimp, Paint) and save it as JPG.

gvControl.EmptyDataText = "<img src='~/images/NoData.jpg' border='0'>"
gvControl.EmptyDataRowStyle.HorizontalAlign = HorizontalAlign.Center

Note: When you use emptydatatext in codebehind donot forget to use databind.

Written by gchandra

October 24, 2007 at 2:17 pm

Posted in Asp.Net, Web Coding

Tagged with , ,