Thursday 30 September 2010

Design Patterns ~ Singleton Pattern using C#

It is considered as the simplest of patterns. Main objective of singleton pattern is to restrict the instantiation of a class to a singe object. It can be implemented like this.

public class Singleton {
private static Singleton _instance;

private Singleton() {


public static Singleton Instance {
if(_instance == null){
_instance = new Singleton();
return _instance;

The above mentioned implementation has advantages and disadvantages. The main advantages are :

  1. Since the instance is created inside the ‘Instance’ property, the class can handle additional functionality like instantiating a subclass.

  2. Lazy Instantiation’ approach. That is, instantiation of the class is not performed, till an object asks for an instance. This will avoid instantiating unnecessary  singletons when the application starts.

And the main disadvantage of this approach is, that this is not ideal for multithreaded environments. If separate threads of execution enter the Instance property method at the same time, more that one instance of the Singleton object may be created. Each thread could execute the following statement and decide that a new instance has to be created.

if(_instance == null)


The most common and suitable solution to overcome this is to use the ‘Double-Check Locking’. This will keep separate threads from creating new instances of the singleton at the same time.

public class Singleton {
private static volatile Singleton _instance;
private static object syncRoot = new object();

private Singleton() {


public static Singleton Instance {
if(_instance == null){
lock (syncRoot) {
if (_instance == null) {
_instance = new Singleton();
return _instance;
This method make sure that only one instance is created and only when the instance is required. Making the variable ‘volatile’ make sure that assignment to the instance variable completes before the instance variable can be accessed. And in order to avoid deadlocks it uses a separate object to lock on, rather than using the type itself.

Saturday 25 September 2010

Removing Duplicate Records From a MS SQL Table – (MS SQL 2005 or above)

Have you ever been in a situation that your SQL tables contain duplicate records, where you have not defined a primary key or an auto increment field. And you need to keep one record and delete the rest.

The usual method of  doing this is to use a temporary table or to use a cursor. But there is another method of doing this using a single query in SQL 2005 or above.

To illustrate this first I will create the following table.

create table SampleTable(
id int not null,
name varchar(20) not null,
age int not null

Now I will insert some duplicate records to the above created table.

insert into SampleTable    (id,name,age) values (1,'John',30)
insert into SampleTable (id,name,age) values (1,'John',30)
insert into SampleTable (id,name,age) values (1,'John',30)
insert into SampleTable (id,name,age) values (1,'John',30)
insert into SampleTable (id,name,age) values (1,'John',30)
insert into SampleTable (id,name,age) values (2,'Mary',26)
insert into SampleTable (id,name,age) values (2,'Mary',26)
insert into SampleTable (id,name,age) values (2,'Mary',26)
insert into SampleTable (id,name,age) values (2,'Mary',26)
insert into SampleTable (id,name,age) values (3,'Ann',25)
insert into SampleTable (id,name,age) values (3,'Ann',25)
insert into SampleTable (id,name,age) values (3,'Ann',25)
insert into SampleTable (id,name,age) values (3,'Ann',25)
insert into SampleTable (id,name,age) values (3,'Ann',25)
insert into SampleTable (id,name,age) values (4,'James',21)


Using the below given query you can easily find out the duplicates (number of duplicate records).

select SUM(rec_count) as rec_count from(
select COUNT (*) - 1 as rec_count from SampleTable group by CHECKSUM(*)
T having COUNT(*) > 1

On the above query I have remove one record (COUNT (*) - 1), since one should be there as a valid record. And you really don’t need ‘having COUNT(*) > 1’, since non duplicate record count(*) will return 1 and count(*)-1 will be 0. It’s there for the ease of readability. So if you execute the above query you will get 11 records as the record count (Total 15 records, 4 valid records. So 15-4 = 11 records).

If you can see I have used ‘CHECKSUM(*)’. This to avoid typing all field names. Without using that the query would be like ‘group by id,name,age’.

And finally we can build the query to delete duplicates like this. First we must find the valid records, which should not be deleted. The way to do is using the function ‘ROW_NUMBER’. Using that we assign a unique row number for each record and select the maximum row number for each group. Then we will only get one record per group.

select MAX(row_num) from (
select ROW_NUMBER() over (order by checksum(*)) as row_num, CHECKSUM(*) as ChkSum
from SampleTable
) as T Group By ChkSum

And if you execute the above query you will get the following result:

Valid Records

It will return row numbers 5,9,14 and 15 as valid records which we must keep. And we must only delete records which the row number is not equal to the ones that’s been returned from the above mentioned query. First we’ll select those records (Only for checking purpose). You can select those records using the following query.

select T.* from(
select ROW_NUMBER() over (order by checksum(*)) as row_num, CHECKSUM(*)
as ChkSum from SampleTable) as T
where T.row_num not in (
select MAX(row_num) from (
select ROW_NUMBER() over (order by checksum(*)) as row_num, CHECKSUM(*)
as ChkSum from SampleTable
) as T Group By ChkSum

And if you execute the above query you will get the following result.

Duplicate Records

So if you see closely row numbers 5,9,14 and 15 are not there. So we can sure, that we are deleting the correct set of records. So in order to delete the duplicated we can use the following query.

delete T from(
select ROW_NUMBER() over (order by checksum(*)) as row_num, CHECKSUM(*)
as ChkSum from SampleTable) as T
where T.row_num not in (
select MAX(row_num) from (
select ROW_NUMBER() over (order by checksum(*)) as row_num, CHECKSUM(*)
as ChkSum from SampleTable
) as T Group By ChkSum

And if you query the table you will get the following result.


Friday 10 September 2010

The Null Coalescing Operator (??)

This operator can be extremely useful in situations where you have to check for the value of a variable and if it's null assign an empty string instead (or any other value).

Well you can achieve this using an if statement.

string zVar = somevalue;
if (somevalue == null) {
zVar = string.Empty;


Or you could use the ternary operator (?:)

string zVar = (somevalue != null) ? somevalue : string.Empty;


But we can do better using the null coalescing operator (??)

string zVar = somevalue ?? string.Empty;

Monday 30 August 2010

Installing Android Lock Screen on iPhone 3GS – IOS4

Run “Cydia” on your iPhone


Go to Manage


Select Sources


Select “Edit


Select “Add


Enter following url:


Select “Done” and go to “SinfuL iPhone Repo


Now select “AndroidLock XT Cracked


Select Install and Confirm


After installation go to “Settings” and setup the application



** Please Note : If you forgot the pattern, do the following steps :


Saturday 21 August 2010

How to Add a Splash Screen to a WPF Application

Adding a Splash Screen to a WPF Application is really easy. For this I will be using VS 2010.

First prepare your image using an image editing application (Such as Photoshop). For this example I will be using the following image that I created using the MSPaint application.



Create a WPF application using VS 2010. And add your Splash Screen image to the project.

Add Existing


And change the build action of your image to “SplashScreen”.

Build Action

And when you run the application you can see the Splash Screen with a fading effect, before the Main Window.

But there are times that we want to keep the splash screen for more than the default time (300 Milliseconds). In order to do that, follow these steps.

Change the application’s build action from “Application Definition” to “Page”

Build Action 2


Create a constructor, and call the “InitializeComponent” method within that.

public App() {

Write your own Main method. And call for the splash screen within that main method. And you can state the amount of time that you wish to keep your splash screen visible.

public static void Main() {
SplashScreen sc = new SplashScreen("Splash.png");
SplashScreenExample.App app = new SplashScreenExample.App();
app.Run(new MainWindow());

Now go to project properties and change the startup object from “Not Set” to your app class name (In this example its “SplashScreenExample.App”).

Startup Object 

Now when you run your application, you can see that the splash screen stays for 4 seconds. (Including the fading time)

Wednesday 18 August 2010

Create table from existing table structure and insert data

Sometimes we might need to create a SQL table from an existing table and insert data from that particular table. So instead of creating the table separately using the ‘CREATE TABLE’ command, we can use the following statement.

select <FieldList> into new_table
from existing_table
<where condition>


select emp_id, emp_fname, emp_lname into emp_temp
from emp_master
where emp_state = 'NY'

** If  you created the table for temporary usage, make sure to drop it, after using it.

Monday 9 August 2010

Create a Multiline TextBox Control using WPF [WPF – Multiline Text Box]

In windows applications we set the “Multiline” property to “true” in order to make a textbox multiline. But in WPF, there’s no property called “Multiline”. In order to make textbox multiline in WPF, you have to set three properties. That is :

  • TextWrapping=”Wrap”
  • VerticalScrollBarVisibility=”True”
  • AcceptsReturn=”True”



<TextBox Name="txtaddress" 

Saturday 15 May 2010

Deploying windows applications using ClickOnce (Visual Studio 2008)

ClickOnce deployment allows you to publish Windows-based applications to a Web server or network file share for simplified installation. Visual Studio provides full support for publishing and updating applications deployed with ClickOnce. ClickOnce deployment is available for projects created with Visual Basic, Visual C#, and Visual J#, but not for Visual C++.
You can publish a ClickOnce application in three different ways: from a Web page, from a network file share, or from media such as a CD-ROM. A ClickOnce application can be installed on an end user's computer and run locally even when the computer is offline, or it can be run in an online-only mode without permanently installing anything on the end user's computer.

Open visual studio 2008 IDE and create a new windows application.

Go to Project –> <Application Name> Properties –> Publish

Publish Location
Publishing folder location can be either web site (, ftp (ftp://mydomain/installation) or file share. If you are using other than a file share to deployment, then you can provide a Installation Folder URL, since the end users may not have the permission to access the publishing folder directly. (Since I am using a shared path, installation folder URL will not be required)

Install Mode and Settings
If you select ‘The application is available online only’, each time it is run, it will be run from the published location and no start menu icon will be created.
But selecting ‘The application is available offline as well’, A shortcut on the Start menu will be created for the application and it will enable the application to be run when the user is disconnected from the network.

Publish Version
Here you should state the publish version (Not the application version). And if you check ‘Automatically increment revision with each publish’ will make sure that the revision number will get incremented automatically when you publish your application.

Application Files
Sometimes it is necessary to publish other files than the application. So this is where you state which ones to include or exclude from the deployment.

You can create a setup file to install the prerequisites, which are required by your application in order to function correctly. And all required prerequisites are selected automatically. But if you want you can either add or remove them from your prerequisites setup.

In this window you should define how your application should be updated. Check ‘The application should check for updates’. And choose whether it should be updated before or after the application starts. If you choose to update it after running the application, you can mention whether you want to check each time it runs or can mention a time period, which it should check. But it is always advisable to check before application starts, so users will get the latest updates each time they run the application.
And mention a minimum required version, so that end user will get the mentioned version of the application, if they have an older version installed on their pc.
If the updating location is other than the publish location, please mention the path.

Save settings and go to the form designer and add a label to the form.
Save and go to Build –> Publish <Application Name>
If you wish do any changes to the publish settings which you completed earlier click next or click on the finish button.
Click next
Click next
And the deployment setup will be created in the published path.
Run the setup.exe to install the application. And click on install button.

Now close the application and change the label to ‘Version’. And go to publish settings and on the update window change the minimum required version to
Click ok and save settings and publish the application.
There will be a start menu shortcut from the first installation.
Click on that to run the application. You will see an update screen and the updated application will be downloaded, installed and executed.
Above mentioned are the basic steps which is required to deploy a .Net windows application using ClickOnce.

For further information please click here

Sunday 2 May 2010

Visual Studio 2010 and Smart Device Development - Disappointing

Visual Studio 2010 does not support mobile application development for versions of Windows Phone prior to Windows Phone OS 7.0.

For information about using Visual Studio 2010 to create applications for Windows Phone OS 7.0, see Windows Phone Development and Silverlight for Windows Phone.

For Visual Studio 2008 mobile developers, Microsoft released the Windows Mobile 6.5 Developer Tool Kit, which works with the Windows Mobile 6 SDK.

Because Visual Studio 2010 does not support mobile application development for Windows Phone prior to Windows Phone OS 7.0, you cannot use the following features: .NET Compact Framework projects, Visual C++ device projects, smart device CAB projects, Device Emulator and Device Emulator Manager, testing tools for device projects, and Device Security Manager.

Mobile application development is still supported in earlier versions of Visual Studio, such as Visual Studio 2008. For more information about smart device projects, see Windows Mobile Developer Center and Smart Device Development in Visual Studio 2008.

VMWare – Shutting down of guests take long time - Resolved

People who uses virtual machines, using vmware might have noticed that when shutting down the guest operating system, it takes hell of a time to shutdown.
This can be fixed by adding these to the .vmx file
prefvmx.minVmMemPct = "100"

mainMem.useNamedFile = "FALSE" 

mainMem.partialLazySave = "FALSE"

mainMem.partialLazyRestore = "FALSE"

Above mentioned filed is located, where the .vmdk file is located.