Error handling with Global.asax and Update Panel

This morning while working with the Global.asax to handle my application level errors, I faced a very strange problem.

Despite of having a Error Handling routine in my Global.asax file, I was unable to trap an exception from the application and instead it was just throwing up a Message Box with the exception message.

So all my routine of logging the error and recording it into the DB was going without being executed.

After a fair bit of research, the UPDATEPANEL came out to be the culprit.

By its very design, UpdatePanels are designed not to bubble up the exception by default and thus it just pops up a Message Box and thus the Error handling routine in Global.asax was never called.

So to call this and feature a full post-back, we need to handle the AsyncPostBackError event of the Script Manager. Here is the code for that.
1. Add the following attribute to the Script Manager

OnAsyncPostBackError="scriptMan_AsyncPostBackError"

2. Create the event handler on the code behind

protected void scriptMan_AsyncPostBackError(object
sender, AsyncPostBackErrorEventArgs e)
{
MethodInfo preserveStackTrace =
typeof(Exception).GetMethod("InternalPreserveStackTrace", BindingFlags.Instance BindingFlags.NonPublic);
preserveStackTrace.Invoke(e.Exception, null);
throw e.Exception;
}

This would bubble up the event and Global.asax would be able to catch the exception thrown and here we could have our all cleanup routine for error trapping and recording.

-- Ashutosh

The row value(s) updated or deleted either do not make the row unique or they alter multiple rows.

This is not a common error to see in the context of today's world, but it is really annoying when it does come up.

This morning while working on a SQL Table, I got this error to come up when I inserted a new row to a table. It did not complain to me when I did an insert on that table, but when I tried to update a few values in that newly added row, it threw up this error.

After a further look down into the issue, I noticed that the table did not had a Primary Key and therefore it allowed me to enter the duplicate records.

Now using SQL Server Management Studio, when I tried to update that row, this error showed up.

Now the worst part, it would not even let you delete that row from the table, since it gets confused which row to delete as there are two rows with exactly same values in the DB.

So below are the two methods to get rid of such an issue.

1. Use "SET ROWCOUNT = 1" when deleting the row.
When you do a

DELETE FROM Table1 where Name = 'ABCD'

it will not work since there are two rows with the value of Name = 'ABCD'
So by simple doing

SET ROWCOUNT = 1
DELETE FROM Table1 where Name = 'ABCD'

it works as it now looks for the first row that matches the criteria and deletes that.

2. Adding an Identity Column
Another way of tackling this problem is adding a new temporary Identity column that would serve as Primary key and we could safely delete the row based on that PK.

ALTER TABLE Table1
ADD TempPKID INT IDENTITY(1, 1)

This will give seperate identity values to both the rows and thus one of them could be deleted by using this column in the where clause.

Component Container

Just recently, one of my collegues came up to me asking if I knew what a .NET developer MUST KNOW as per MSDN.... and fired me a simple straight question.....


WHAT IS A COMPONENT CONTAINER ??


Well the question was straight and simple, but certainly the answer was not. Not atleast for me.


So I quick fired MSDN and searched for the same.


Here is what it says:

The IContainer that contains the Component, if any, or nullNothingnullptra null
reference (Nothing in Visual Basic) if the Component is not encapsulated in an
IContainer.

Does not really a help for someone new to the concept. So I expanded my search to google. And off came quite a few results. Now uptill now, this is what I could understand and would CERTAINLY WELCOME OTHERS THOUGHTS ON IT

Javascript Rounding

Just discovered:

Math.Round() function in Javascript return only the nearest whole number for any values.

So Math.Round(4.366) = 4
and Math.Round(8.33345) = 8.

We had a problem where we also needed to have the number rounded upto 2 or 3 decimal places.

Here is a way of doing the same:

function RoundNumber(Number, decimal)
{
var orgNumber = Math.round(Number*(Math.pow(10,decimal)));
var result = orgNumber /(Math.pow(10,decimal));
return result;
}


-- Ashutosh

Google AJAX Search API

Hi,

While browsing through, I just stumblled upon what is known as Google AJAX Search API.

I was in seach of something where I could encorporate a google search right into my blog and which looks a touch different than the normal search page from google.

And I did well to land upon the Google AJAX Search API

It was quite simple and had enough tutorials and sample codes written for someone looking to encorporate a decent search into their site.

Take a look at the search box at the right bar on the blog. And try searching for something through it. It displays the results for each category as a seperate tab on the very same page.

Here is the way to encorporate the same in your blog.

1. Obtain a Google API Key. This is a kinda composite key for all the services of google that we would be using.

2. Integrate the API key code into your blog. OPen your blog and go to Edit HTML and in the head section of your blog, add the following script tag:

<script src='http://www.google.com/jsapi?key=developer_key'
type='text/javascript'/>

3. This will allow us to use all the services that google offers. Now we need to put up the code for displaying the search box. Here is the code for that.

<script type="'text/javascript'">
google.load("search", "1");

// Call this function when the page has been loaded

function initialize()
{

var searchControl = new google.search.SearchControl();

searchControl.addSearcher(new GwebSearch());

searchControl.addSearcher(new GvideoSearch());

searchControl.addSearcher(new GblogSearch());

searchControl.addSearcher(new GnewsSearch());

searchControl.addSearcher(new GimageSearch());

searchControl.addSearcher(new GbookSearch());

// create a drawOptions object

var drawOptions = new GdrawOptions();
// tell the searcher to draw itself in tabbed mode

drawOptions.setDrawMode(GSearchControl.DRAW_MODE_TABBED);
drawOptions.setSearchFormRoot(document.getElementById("searchPlaceHolder"));
searchControl.draw(document.getElementById("searchcontrol"), drawOptions);

}

google.setOnLoadCallback(initialize);
</script>

4. An explaination of this code is as below:
a. google.load("search", "1"); - This line of code prepares the search API from google and loads all the functions necessary to perfrom the search.

b. google.search.SearchControl();- This is the main control that displays the search results.

c. searchControl.addSearcher(new GwebSearch());- This is used to add various searchers to the control. Add as many searches as you like.

d. GdrawOptions();- A draawoptions object gives you the flexibility of customizing your search results display. The below two lines show the examples of its usage.

e. drawOptions.setDrawMode(GSearchControl.DRAW_MODE_TABBED); - This tells the search control how to display the search results. Here we have set it to display in the form of different tabs.

f. drawOptions.setSearchFormRoot(document.getElementById("searchPlaceHolder"));- This tells the search option the control to which the search box would be bind. I created a div with the ID searchPlaceHolder to hold my search box.

g. searchControl.draw(document.getElementById("searchcontrol"), drawOptions); - This is used to actually draw the search control with the appropriate draw options.

h.

Loading

- This provides us with an instance of a searchcontrol. Place it where you want the results to be displayed.

This way it would display a search box where you place the searchPlaceHolder control and would display the search results where you place the searchcontrol.


Hope this helps a lot of people like me ....

-- Ashutosh

Harbhajan Banned for 3 test matches.......

Yes this indeed is a technical blog but being a sentimental Indian, I could not stop myself from writing my own views of the story.

First of all, comments from a few commendable people:

• "I am South African, and I understand the word racism. - Mike Proctor"

• "They're entitled to do whatever they think is appropriate at the time but for me that would be a little bit extreme, I must admit. - Ricky Ponting"

• "What to do? Calls for sackings are knee-jerk, the threat to abandon the tour nonsensical. Apart from anything else, the all-powerful television moguls here and in India would not countenance it. The tour will go on, and so will the captains. So law and order it must be. - Greg Baum (The AGE)"

• "I saw the footage of what had happened involving Andrew Symonds when the
  Australians were in India. Most of the spectators were just having some light-hearted banter, and there was no malice in most cases. - Steve Waugh"

• "Michael Clarke also had a dreadful match but he is a young man and has time to rethink his outlook. That his mind was in disarray could be told from his batting. In the first innings he offered no shot to a straight ball and in the second he remained at the crease after giving an easy catch to slip. On this evidence Clarke cannot be promoted to the vice-captaincy of his country. - Peter Roebuck"

• There are times when you don't know. So, you ask the question. Every player has right to ask the umpire. I will say I don't appeal if I don't think they are out. If I am not sure, I will ask the umpire and I'll accept his decision. - Adam Gilchrist"

SO these are the view of certain people who are known to be experts of their own fields.
Well Mr. Mike Proctor just to let you know, We are the citizens of India and We really do not know what RACISM is. We never hear such words in our country because we never had views and culture as in SA our even Australia where people are discriminated on the basis of color.

And the statement from a reputed person from Australia "WHY SYMONDS ONLY !!" confirms the stand that they still have racism running through their blood. I mean had the same statement been made against Ponting or any white cricketer that would have not been a Racial comment but since it has been againsta Black, it is definitely the ONE..........

Regarding cancellation of the tour - As an Indian, yes I would most definitely like it to happen, but as an ardent cricket fan, I would most definitely like the tour to go on. Because the fight from here on would definitely be an interesting one becuase now it would most certainly not be a mere game of cricket but it would be a question of the national pride at stake.

As Greg Baum quoted - The television media that is presenting the live coverage all over the world is strong enough to make the tour continue. There would be a huge loss to the industry if it does not. After all we are talking of around 3 months of cricket going out of question.

And lastly, to comment on what Adam Gilchrist had to say on Rahul Dravid's dismissal, well Gilli your statement suggests that you were not confirm if that was out or not so you had put up a question to bucknor asking for his openion.

Well I would leave that to the readers to decide upon after having a look at the footage of the dismissal.


--Ashutosh

Double v/s Decimal

Just recently, one of my Colleagues approached me with a very strange problem. He had made a function for Rounding the numbers to the specified number of decimal places.

He was facing a problem where his function would Round off 544.435 to 544.43 but would Round off 544.445 to 544.45 which was the intended one.

After a fair bit of research I could conclude the following:

The error was because he was taking input and providing the output as DOUBLE.

Now MSDN says that DOUBLE is a FLOATING POINT VARIABLE Type. It takes up less space in the memory but is prone to some Rounding problems.

So while storing the above two DOUBLES, .NET stored them as follows:

544.435 ------------- 544.43499999999994543031789362430572509765625
544.445 ------------- 544.4450000000000500222085975110530853271484375

So doing a Multiplication with the precision factor (100 in this case) and taking a Math.Floor of that number converts

544.435 to 544.43
&
544.445 to 544.45

More explanation about the Binary Floating point could be found at

http://www.yoda.arachsys.com/csharp/floatingpoint.html

BTW, the solution to the above mentioned problem is using something that is Fixed Point Variable and not a Floating Point Variable like Double.

So using DECIMAL instead of DOUBLE in the application resolves the Rounding Issue.


-- Ashutosh

Garbage Collection

Thanks to marble_eater for the article which is now in the form of a slideshow.......

If you wish to download the presentation, it can be downloaded from here

Why is a Short of 4 bytes

Why is a Short of 4 bytes

This is where it all started. I faced an interesting problem while working on my Sessions application. Declaring a structure as :

Struct ShortInt
{
Short firstShort;
Int32 secondInt;
}

If someone is asked about the size of this structure. I bet most people would answer it as I did : 6 bytes.

But surprisingly, the answer is 8 bytes.

Simple reason for that being the memory is allocated in the chunks and if the declaration of structure is done wisely, it could save a lot of memory:

Taking example:

Struct exampleStruct
{
Byte b1;
Int32 i;
short s;
Byte b2;
}

Here if we look at this structure, the memory for this block is allocated as follows:
Byte b1 ----- A chunk of 4 bytes is allocated
Int32 i ------ This chunk has only 3 bytes left so a new chunk of 4 bytes alloted
short s ------ Previous chunk is full. So next 4 byte chunk is alloted.
Byte b2 ----- Previous chunk has 2 bytes left and can accomodate a byte. Hence the byte variable is accomodated in teh same chunk.

So total size becomes 12 bytes.

Now if we redefine our structure as follows:

Struct
exampleStruct
{
Byte b1;
Byte b2;
short s;
Int32 i;
}

Now the memory allocation would be as follows:

Byte b1 ----- A chunk of 4 bytes is alloted
Byte b2 ----- A byte in teh same chunk
short s ------ Previous chunk has 2 bytes left in it
Int32 i ----- Since the previous chunk is full, a new chunk is alloted

Hense the total size is 8 bytes only.

More could be found on the following links :

http://www.vsj.co.uk/articles/display.asp?id=501
http://msdn.microsoft.com/msdnmag/issues/05/01/MemoryOptimization/default.aspx



--Ashutosh

SecureString in c#

System.Security.SecureString



Per MSDN:

Represents text that should be kept confidential. The text is encrypted for privacy when being used, and deleted from computer memory when no longer needed. This class cannot be inherited.



Storing any sensitive data like passwords etc in the standard System.String can be a potential threat to the data for the following reasons:

>> It is stored on the Managed Heap and is not pinned in the memory, so the garbage collector can move it around at will leaving several copies in memory. The code will not know that this has happened, and even if it could figure out that the string was moved, there is no way to clear out the other copies. Instead we have to wait for the CLR to allocate another object where the sensitive data is so that the memory gets erased.

>> It's not encrypted, so anyone who can read process's memory will be able to see the value of the string easily. Also, if the process gets swapped out to disk, the unencrypted contents of the string will be written to the swap file.

>> It's not mutable, so whenever it is modified, there will be the old version and the new version both in memory

>> Since it's not mutable, there's no effective way to clear it out when you're done using it

Hence, .NET 2.0 introduced a new class under System.Security namespace called SecureString, that can be used in place of standard Strings to store sensitive values.

Using SecureString eliminates the above mentioned issues as:

>> The SecureString is not stored in the managed heap while standard strings are and therefore it will not be replicated to multiple locations in memory.

>> SecureStrings are stored in an encrypted form. They need to be decrypted when they are used. this period of decryption can be kept as small as possible. So even if the process is swapped out to disk while the string is encrypted, the plaintext will not end up in the swap file.

>> The keys used to encrypt the string are tied to the user, logon session, and process. This means that any minidumps taken of the process will contain secure strings which are not decryptable.

>> SecureStrings are securely zeroed out when they're disposed of. System.Strings are immutable and cannot be cleared when you've finished with the sensitive data

create a SecureString, you append one character at a time:

System.Security.SecureString secString = new System.Security.SecureString();
secString.AppendChar(p);
secString.AppendChar('a');
secString.AppendChar('s');
secString.AppendChar('s');
secString.AppendChar('w');
secString.AppendChar('d');

When the string contains the data you want, you can make it immutable and uncopyable by calling the MakeReadOnly method:

secString.MakeReadOnly();

To read the secure value, use the SecureStringToBSTR() method as follows:

IntPtr ptr = System.Runtime.InteropServices.Marshal.SecureStringToBSTR(secString);
string sDecrypString = System.Runtime.InteropServices.Marshal.PtrToStringUni(ptr);

The garbage collector will remove SecureStrings when they're no longer referenced, but you
can dispose of a SecureString by using the Dispose() method:

secString.Dispose();