March 2012 Entries
App_Offline.htm, taking site down for maintenance

There is much simpler and graceful way to shut down a site while doing upgrade to avoid the problem of people accessing site in the middle of a content update.


Basically, if you place file with name 'app_offline.htm' with below contents in the root of a web application directory, ASP.NET will shut-down the application,  and stop processing any new incoming requests for that application. 

ASP.NET will also then respond to all requests for dynamic pages in the application by sending back the content of the app_offline.htm file (for example: you might want to have a “site under construction” or “down for maintenance” message).


Then after upgrade, just rename/delete app_offline.htm file…and the site would be back to normal.

Just remember that the size of the file should be greater than 512 bytes, doesn't matter even if you add some comments to it to push the byte size as long as it's of the size greater than 512 - it'll work fine.



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<html xmlns="" >
    <title>Maintenance Mode - Outage Message</title>
    <h1>Maintenance Mode</h1>

    <p>We're currently undergoing scheduled maintenance. We will come back very shortly.</p>
    <p>Sorry for the inconvenience!</p>

    Adding additional hidden content so that IE Friendly Errors don't prevent
    this message from displaying (note: it will show a "friendly" 404
    error if the content isn't of a certain size).
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 
    <h2>Site under maintenance...</h2> 




Posted On Wednesday, March 28, 2012 4:25 PM | Comments (10)
Show line breaks in asp:label inside gridview

To show line breaks in asp:label element or for that matter inside Gridview, do the following  in case of Mandatory/ Nullable fields.

<%# ((string)Eval("Details")).Replace("\n", "<br/>")
<%# FormatString(Eval("Details"))


In code behind, add the following FormatString function -


string FormatString(string strHelpMessage)


string rtnString = string.Empty;

if (!string.IsNullOrEmpty(strHelpMessage))

rtnString = strHelpMessage.Replace(

Environment.NewLine, "<br/>");

return rtnString;


Posted On Thursday, March 22, 2012 4:02 PM | Comments (3)
Page_BlockSubmit - reset it to False, if there is a scenario when page doesn't postback on validation error

Recently, I was facing a problem where if there was a validation error, and if I changed the state of checkbox it won't postback on first attempt. But when I uncheck and check again , it postbacks on second attempt...this is some quirky behaviour in .ASP.Net platform.

The solution was to reset Page_BlockSubmit flag to false and it works fine.

The following explanation is from


Submit button on the page is a member of vgMain, so automatically it will only run the validation on that group. A solution is needed that will run validation on multiple groups and block the postback if needed.


Include the following function on the page:

function DoValidation()
   //validate the primary group
   var validated = Page_ClientValidate('vgPrimary ');
   //if it is valid
   if (validated)
      //valid the main group
      validated = Page_ClientValidate('vgMain');
   //remove the flag to block the submit if it was raised
   Page_BlockSubmit = false;
   //return the results
   return validated;

Call the above function from the submit button’s OnClientClick event.

<asp:Button runat="server" ID="btnSubmit" CausesValidation="true" 
   ValidationGroup="vgMain" Text="Next" OnClick="btnSubmit_Click"
   OnClientClick="return DoValidation();"  />

What is Page_BlockSubmit

When the user clicks on a button causing a full post back, after running Page_ClientValidate ASP.NET runs another built in function ValidatorCommonOnSubmit. Within Page_ClientValidate, Page_BlockSubmit is set based on the validation. The postback is then blocked in ValidatorCommonOnSubmit if Page_BlockSubmit is true. No matter what, at the end of the function Page_BlockSubmit is always reset back to false.

If a page does a partial postback without running any validation and Page_BlockSubmit has not been reset to false, the partial postback will be blocked. In essence the above function, RunValidation, acts similar to ValidatorCommonOnSubmit. It runs the validation and then returns false to block the postback if needed. Since the built in postback is never run, we need to reset Page_BlockSubmit manually before returning the validation result.

Posted On Thursday, March 22, 2012 3:59 PM | Comments (5)
Update Query in SQL with SELECT statement
Table.col1 = other_table.col1, 
Table.col2 = other_table.col2 
ON = 
Posted On Tuesday, March 13, 2012 4:16 PM | Comments (2)
ThrowIfMaxHttpCollectionKeysExceeded error message when doing postback

Microsoft recently (12-29-2011) released an update to address several serious security vulnerabilities in the .NET Framework. One of the fixes introduced by MS11-100 temporarily mitigates a potential DoS attack involving hash table collisions. It appears this fix breaks pages that contain a lot of POST data. In our case, on pages that have very large checkbox lists. Why would this be the case?

There are some information on this limit to be at if your webpage was working fine earlier and it all of a sudden started crashing with the following message -

"Operation is not valid due to the current state of the object." whenever a post back is done.

the stack trace is

at System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded() at System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding) at System.Web.HttpRequest.FillInFormCollection()

Then  probably you have crossed the default limit for the postdata collection key.

To overcome this limit, add the following line of code in you <appsetting> section of web.config

<add key="aspnet:MaxHttpCollectionKeys" value="2001" />

Hope this helps someone..           

Posted On Monday, March 5, 2012 4:05 PM | Comments (19)