asp.net interview questions

When I create a new ASP.NET 4 web application, the web.config file is almost empty. What happened to all the configuration elements that were there prior to ASP.NET 4?

2011-12-12T11:53:00.000-08:00

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All the major configuration settings are moved into machine.config file, and all the applications will inherit the setting from this file. If an application needs to override the default settings, we can do so using the application specific configuration (web.config) file. ASP.NET 4 applications have clean web.config files.

If you create a new asp.net 4 empty web application, the only entry that you will find is shown below.

Note: If you create a new ASP.NET Web Application, instead of a new ASP.NET Empty Web Application, you will find a lot more confiuration entries in the web.config file. This is because, the template for ASP.NET web application overrides some of the default settings inherited from machine.config.

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Difference between EnableViewState and ViewStateMode properties

2011-12-09T10:21:00.000-08:00

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1. Using EnableViewState property we only have 2 options
We can turn off view state altogether,
or
Enable viewstate for the entire page and then turn it off on a control-by-control basis.

2. If you want to turn of ViewState for the entire page and only enable it for specific controls on the page, then we have to use ViewStateMode property in conjunction with EnableViewState.

3. EnableViewState property only accepts true or false values and the default value is true, where as ViewStateMode property can have a value of - Enabled, Disabled and inherit. Inherit is the default value for ViewStateMode property.

4. ViewStateMode property is introduced in ASP.NET 4, where as EnableViewState exists from a long time.

5. If EnableViewState is to True, only then the ViewStateMode settings are applied, where as, if EnableViewState is set to False then the control will not save its view state, regardless of the ViewStateMode setting. In short if EnableViewState is set to False, ViewStateMode setting is not respected.

6. To disable view state for a page and to enable it for a specific control on the page, set the EnableViewState property of the page and the control to true, set the ViewStateMode property of the page to Disabled, and set the ViewStateMode property of the control to Enabled.

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Dot Net Videos

2011-11-28T13:52:00.000-08:00

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What are generics?

What is a SQL Injection Attack?

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ASP.NET Page is very slow. What will you do to make it fast

2011-09-03T08:26:00.000-07:00

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This is a very common asp.net interview question asked in many interviews. There are several reasons for the page being slow. We need to identify the cause.

1. Find out which is slow, is it the application or the database : If the page is executing SQL queries or stored procedures, run those on the database and check how long do they take to run. If the queries are taking most of the time, then you know you have to tune the queries for better performance. To tune the queries, there are several ways and I have listed some of them below.
   a) Check if there are indexes to help the query
   b) Select only the required columns, avoid Select *.
   c) Check if there is a possiblity to reduce the number of joins
   d) If possible use NO LOCK on your select statements
   e) Check if there are cursors and if you can replace them with joins

2. If the queries are running fast, then we know it is the application code that is causing the slowness. Isolate the page event that is causing the issue by turning tracing on. To turn tracing on, set Trace="true" in the page directive. Once you have tracing turned on you should see trace information at the bottom of the page as shown in the image below. In this case Page Load event is taking the maximum time. So we know, the code in Page_Load event is causing the issue. Once you look at the code, you should be able to nail down the issue.

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What is SQL Injection Attack

2011-07-21T13:03:00.000-07:00

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Let us understand SQL injection attack, with an example. I have an Employee Search Page as shown in the image below. This webform has a very simple functionality. You enter the ID of the employee, you want to search and click the Search Employee button. If a match is found in the database, we show the employee record in the GridView.

Employee Search Page

The HTML for the Employee Serach Page is shown below. As you can see from the HTML, the Employee Serach Page contains TextBox, Button and a GridView control.

Employee Search Page HTML

The codebehind page for the EmployeeSearchPage is shown below.

Employee Search Page Code Behind

The Button1_Click event handler has the required ADO.NET code to get data from the database. This code is highly susceptible to sql injection attack and I will never ever have code like this in production environment. The second line in Button1_Click event handler, dynamically builds the sql query by concatenating the Employee ID that we typed into the TextBox.

So, for example, if we had typed 2 into the Employee ID textbox, we will have a SQL query as shown below.
Select * from Employees where Id=2

If a malicious user, types something like 2; Delete from Employees into the TextBox, then we will have a SQL query as shown below.
Select * from Employees where Id=2; Delete from Employees

When this query is executed, we loose all the data in the Employees table. This is SQL Injection Attack, as the user of the application is able to inject SQL and get it executed against the database. It is very easy to avoid SQL Injection attacks by using either parameterized queries or using stored procedures.

You may be thinking, how will the user of the application know the name of the table. Well, one way is to simply guess or inject a sql syntax error. The injected SQL syntax error causes the page to crash and can possibly reveal the name of the table as shown below. However, proper exception handling and custom error pages can be used to prevent the end user from seeing the yello screen of death. The screen shot below shows the table name Employees.

Page crash revealing Employees table name

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Reusable SQL function to split a string

2011-07-12T10:21:00.000-07:00

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Write a reusable split function that can be used to split any given string with a given delimiter?

To further understand the question better, consider the examples below
Input String : 123|456|234|435
Delimiter Character : |
The output should be as shown below:
101
102
103
104
105

Create Function SplitFunction (@InputString nvarchar(max), @Delimiter Char(1))
Returns @ResultTable Table (Items nvarchar(4000))
as
Begin
   Declare @Index int
   Declare @Slice nvarchar(4000)
   Set @Index = 1

   If(@InputString is null)
   Begin
      Return
   End

   While (@Index != 0)
   Begin
      Set @Index = CHARINDEX(@Delimiter, @InputString)

      If(@Index != 0)
         Begin
            Select @Slice = LEFT(@InputString, @Index - 1)
         End
      Else
         Begin
            Select @Slice = @InputString
         End

      Insert into @ResultTable(Items) Values (@Slice)

      SET @InputString = RIGHT(@InputString, LEN(@InputString) - @Index)

      If(LEN(@InputString)) = 0
      Begin
         Break;
      End
End
Return
End

When we execute Select * from SplitFunction('123|456|234|435','|'), we get the desired output. You may try with different inputs and delimiters.

This split function is a classic example for multi-statement table valued function in SQL server.

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Interview Questions related to Dependency Injection

2011-06-09T10:59:00.000-07:00

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It is very important that, you understand the concept of dependency injection before you read these questions. Please read Dependency Injection with an example article if you have not done so already.

When do you use Setter Injection over Constructor Injection and vice versa ?
Constructor Injection is normally the standard for dependency injection. Constructor Injection, ensures that all the dependency objects are initialized before we attempt to invoke any methods or peroperties, thus avoiding null reference exceptions.

Setter Injection is used rarely in exceptional cases. For example, if I have a class that has several methods which does not depend on any other objects, and now I need to introduce a new method with in this class, which depends on another object. We can use, constructor injection here, but we need to change the exisitng constructor calls at all the other places. This can become cumbersome, especially if the project is a huge one. Hence, Setter Injection could be a choice when we want to change the legacy code.

Setter Injection, enables you to inject the object, just before you need it. So, if the object is an expensive object to create, and you want to create it as late as possible, then setter injection is your choice.

What are the advantages of using Dependency Injection?
1. Dependency Injection allows us to develop very loosely coupled systems.

2. Easy to swap in a different implementation of a component, as long as the component implements the interface type.

3. Dependency Injection, allows objects to be mocked with in the Unit Tests. This is the greatest advantage of Dependency Injection.

What Dependency Injection Container have you used in your project?
There are lot of Dependency Injection Containers available in the market. I have included, the very commonly used list of Dependency Injection Containers for your quick refernce.
1. Unity
2. Castle Windsor
3. StructureMap
4. Spring.NET

I have used Unity in most of my projects.

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Explain Dependency Injection with an example

2011-06-08T13:32:00.000-07:00

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One of the very common interview questions, asked these days. This is the most common approach used today to solve dependencies between objects. In many of the enterprise class ASP.NET application, Dependency Injection is a common standard to follow. Let us understand Dependency Injection with an example.

In the example above, Employee class depends on EmployeeDAL class to get the data from the database. In GetAllEmployees() method of the Employee class, we create an instance of the EmployeeDAL (Employee Data Access Layer) class and then invoke SelectAllEmployees() method. This is tight coupling, EmployeeDAL is tightly copuled with the Employee class. Everytime the EmployeeDAL class changes, the Employee class also needs to change. EmployeeDAL cannot be mocked and hence unit testing becomes cumbersome and time consuming.

The same example can be re-written using dependency injection as shown below. First thing to notice is that, we are using interface types instead of concrete types. Using interfaces help us to plugin any implemenation of the interface, with less or no code modification at all. We are not creating the instance of the EmployeeDAL in the Employee class, instead we are passing it as a parameter to the constructor of the Employee class. As, we are injecting an instance of a class into a class that depends on it, we can call this process as Dependency Injection.

Dependency Injection is of 2 types.
1. Constructor Injection
2. Setter Injection.

We have already seen how to use Constructor Injection in the example above. An, example for Setter Injection is shown below. We are injecting an object instance through the Setter property, instead of a constructor. Hence, we call Setter Injection. It is very important to use the property EmployeeDataObject to access the instance of IEmployeeDAL, rather than the private variable employeeDAL. The property checks to see if employeeDAL is null, and throws the exception accordingly.

For other follow up interview questions on Dependency Injection, please read the articles below.
1. When do you choose Setter Injection over Constructor Injection and vice versa ?
2. What are the advantages of using Dependency Injection ?
3. What Dependency Injection Container have you used in your project ?

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Interview Questions related to strong named assemblies

2011-06-06T13:53:00.000-07:00

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Can you copy a weak named assembly into GAC?
No, an assembly has to be strongly named to be copied into the GAC

What is the difference between a strong and weak named assemblies?
The following are the differences between a strong and weak named assemblies
1. Weak named assemblies can be duplicated and tampered with, where as strong named assemblies cannoth be tampered and duplicated.

2. Strong named assemblies can be copied into GAC, where as weak named assemblies cannot be copied.

3. A single copy of strong named assembly present in the GAC can be shared with multiple applications, where as weak named assembly must be copied into the bin directory of each project.

What is the main advantage of strong naming an assembly?
A shared assembly that is strongly named solves the DLL hell problem, that microsoft is notoriously known for. Please follow the articles below, to understand DLL hell and the solution.
What is DLL hell
How is DLL hell problem solved

Can a strong named assembly refer, a weak named assembly and why?
No, a strong named assembly cannot reference, another weak named assembly. If this is possible, the DLL hell problem will reoccur.

Explantion: When you reference a strong named assembly, you expect to get certain benefits, such as versioning and naming protection. If the strong named assembly then references an assembly with a simple name, which does not have these benefits, you lose the benefits you would derive from using a strong named assembly and revert to DLL conflicts. Therefore, strong named assemblies can only reference other strong named assemblies.

What is the downside of strong naming an executable (.EXE) ?
A strongly named assembly cannot reference a weak named assembly. Therefore, strong naming an EXE prevents the EXE from referencing weak named dlls, that are deployed with the application. For this reason, the Visual Studio project system does not strong name application EXEs. Instead, it strong-names the Application manifest, which internally points to the weak named application EXE. In addition, you may want to avoid strong-naming components that are private to your application. In this case, strong-naming can make it more difficult to manage dependencies and add unnecessary overhead for private components.

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What is the process for strong naming an assembly

2011-06-06T12:48:00.000-07:00

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What is the process for strong naming an assembly ?
or
What is the purpose of strong naming tool ( sn.exe ) in .NET ?

In .NET, the assembly name usually consists of 4 parts as listed below.
1. Simple Textual Name
2. Version Number (The version number is also divided into 4 parts)
3. Culture
4. Public Key Token

If an assembly contains, all the 4 parts, then the assembly is a strongly named assembly, other wise the assembly is called as a weak named assembly. In general, when you compile any .NET application, the generated assembly by default will have the Simple Textual Name, Version Number and Culture but not the public key token. If you have to sign the assembly with a public key token, you first have to generate the key pair using key generation tool called strong naming tool (sn.exe). The generated key pair will consist of a private and a public key and are written into a key file. Key files have the extension of .snk.

We now have to associate the key file with the project, so that when we compile the project, the generated assembly is signed using the key pair. To do this, In AssemblyInfo.cs file of the project, specify AssemblyKeyFile attribute as shown below.
[assembly: AssemblyKeyFile("MyKey.snk")]

The last and final step is to build the project which will automatically sign the assembly using the key file. This process generates the strongly named assembly.

In short, there are 3 simple steps to generate a strongly named assembly.
1. Generate the key pair using strong naming tool, SN.exe.

2. Associate the generated Key file to the project using AssemblyKeyFile, which is present in AssemblyInfo.cs file.

3. Build the project.

Once, you have strongly named the assembly, you can copy it to GAC. There are 2 ways to copy an assembly into GAC.
1. Using simple drag and drop : Drag the generated assembly into the GAC folder. Usually the path for GAC is c:\windows\assembly. On some machines this could be c:\winnt\assembly.

2. Use GAC utility : Use GAC Utility tool(gacutil.exe) as shown below in visual studio command prompt.
gacutil.exe -i C:\MyAssembly.dll (- i stands for install)

Once, you have successfuly copied the assembly into GAC, notice the four parts of the assembly name. The culture column could be empty, indicating that the assembly is language neutral.

Please click here to read few other follow up interview questions related to strong named assemblies.

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ASP.NET Interview Questions Index

2011-06-03T11:18:00.000-07:00

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2011-06-02T12:42:00.000-07:00

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How is the DLL HELL problem solved in .NET

2011-06-01T12:20:00.000-07:00

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Please read What is dll hell? interview question, before proceeding with this article.

In short, the dll hell problem is solved in .NET by signing the shared assemblies with strong name. Please follow this article, to understand the process of strong naming an assembly.

In dot net all the shared assemblies are usually in the GAC. GAC stands for Global Assembly Cache. The path for GAC is C:\[OperatingSystemDirectory]\assembly. For example on my computer the path is C:\WINDOWS\assembly. The image below shows the shared assemblies in the GAC.

Only strong named assemblies can be copied into GAC. Strong named assemblies in .NET has 4 pieces in its name as listed below.
1. Simple Textual Name
2. Version Number
3. Culture
4. Public Key Token

All these four pieces put together, is called as the fully qualified name of the assembly. In the GAC image above Accessibility assembly has a version of 2.0.0.0.

Now consider the example below:
1. I have 2 applications, Application - A1 and Application - A2 which relies on the shared assembly Accessibility.dll (Version 2.0.0.0) as shown in the image below.

2. Now, I have a latest version of Application - A2 available on the internet.
3. I download the latest version of A2 and install it on my machine.
4. This new installation copies a newer version of Accessibility.dll into the GAC with version 3.0.0.0.
5. So, in the GAC we now have 2 versions of Accessibility.dll.
6. Application - A1 continues to use Accessibility.dll (version 2.0.0.0) and Application - A2 uses Accessibility.dll (version 3.0.0.0)
7. So, now the assemblies are able to reside side by side in the GAC. For this reason dot net assemblies are also said to be supporting side by side execution.

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What is DLL HELL in .NET

2011-05-31T11:57:00.000-07:00

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Let us try and understand DLL HELL problem with an example. Please refer to the image below. If you want to know how dll hell problem is solved in .net, you can read this article.

1. I have 2 applications, A1 and A2 installed on my computer.

2. Both of these applications use shared assembly shared.dll

3. Now, I have a latest version of Application - A2 available on the internet.

4. I download the latest version of A2 and install it on my machine.

5. This new installation has over written Shared.dll, which is also used by Application - A1.

6. Application - A2 works fine, but A1 fails to work, because the newly installed Shared.dll is not backward compatible.

So, DLL HELL is a problem where one application will install a new version of the shared component that is not backward compatible with the version already on the machine, causing all the other existing applications that rely on the shared component to break. With .NET versioning we donot have DLL HELL problem any more.

How is the DLL HELL problem solved in .NET, is another very important .net interview question. Click here to read.

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ASP.NET Interview Questions by topic

2011-05-22T03:49:00.000-07:00

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What are the advantages and disadvantages of a layered architecture

2011-03-10T14:39:00.000-08:00

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The following are the advantages of a layered architecture:

Layered architecture increases flexibility, maintainability, and scalability. In a Layered architecture we separate the user interface from the business logic, and the business logic from the data access logic. Separation of concerns among these logical layers and components is easily achieved with the help of layered architecture.

Multiple applications can reuse the components. For example if we want a windows user interface rather than a web browser interface, this can be done in an easy and fast way by just replacing the UI component. All the other components like business logic, data access and the database remains the same. Layered architecture allows to swap and reuse components at will.

Layered architecture enables teams to work on different parts of the application parallely with minimal dependencies on other teams.

Layered architecture enables develop loosely coupled systems.

Different components of the application can be independently deployed, maintained, and updated, on different time schedules.

Layered architecture also makes it possible to configure different levels of security to different components deployed on different boxes. sO Layered architecture, enables you to secure portions of the application behind the firewall and make other components accessible from the Internet.

Layered architecture also helps you to test the components independently of each other.

The following are the disadvantages of a layered architecture:

There might be a negative impact on the performance as we have the extra overhead of passing through layers instead of calling a component directly.

Development of user-intensive applications can sometime take longer if the layering prevents the use of user interface components that directly interact with the database.

The use of layers helps to control and encapsulate the complexity of large applications, but adds complexity to simple applications.

Changes to lower level interfaces tend to percolate to higher levels, especially if the relaxed layered approach is used.

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What is the difference between layers and tiers

2011-03-10T14:31:00.000-08:00

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Layers refer to logical seperation of code. Logical layers help you organise your code better. For example an application can have the following layers.

1)Presentation Layer or UI Layer
2)Business Layer or Business Logic Layer
3)Data Access Layer or Data Layer

The aboove three layers reside in their own projects, may be 3 projects or even more. When we compile the projects we get the respective layer DLL. So we have 3 DLL's now.

Depending upon how we deploy our application, we may have 1 to 3 tiers. As we now have 3 DLL's, if we deploy all the DLL's on the same machine, then we have only 1 physical tier but 3 logical layers.

If we choose to deploy each DLL on a seperate machine, then we have 3 tiers and 3 layers.

So, Layers are a logical separation and Tiers are a physical separation. We can also say that, tiers are the physical deployment of layers.

Tiers:
1) Presenation Tier or UI Tier (Hosts the Presentation Layer or UI Layer). This can be considered as web server in case of an ASP.NET web application.
2) Application Tier or Business Tier (Hosts Business Layer or Business Logic Layer).
3) Data Access Tier or Data Tier (Hosts Data Access Layer or Data Layer).
4) Database Tier - SQL Server or Oracle (or any other database) which has tables, stored procedures and other database objects.

In general the following are the responsibilities of each layer or tier:

1)Presentation Layer or Tier is usually responsible for interacting with the user.
2)Business Layer or Tier is responsible for implementing the business logic of the application.
3)Data Access Layer or Tier is responsible for encapsulating the code that accesses the persistent data stores such as a relational database.

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What is the difference between const and static read-only member?

2010-06-27T06:04:00.000-07:00

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A const field must be initialized at the place where it is declared as shown in the example below.
class Program
{
      public const int Number = 100;
}
It is a compile time error to declare a const without a value. The code below will generate a compiler error stating "A const field requires a value to be provided"
class Program
{
      public const int Number;
}
It is a compile time error to change the value of a constant. The following code will generate a compiler error stating "The left-hand side of an assignment must be a variable, property or indexer"
class Program
{
     public const int Number = 100;
     static void Main()
     {
           Number = 200;
     }
}

It is not mandatory to initialize a static readonly field where it is declared. You can declare a static readonly field without an initial value and can later initialize the static field in a static constructor as shown below.
class Program
{
     public static readonly int Number;
     static Program()
     {
           Number = 100;
     }
}

Once a static readonly field is initialized, the value cannot be changed. The code below will generate a compiler error stating "A static readonly field cannot be assigned to (except in a static constructor or a variable initializer)"
class Program
{
       public static readonly int Number;
       static Program()
       {
             Number = 100;
       }
       static void Main()
       {
              Number = 200;
        }
}

In short, the difference is that static readonly field can be modified by the containing class, but const field can never be modified and must be initialized where it is declared. A static readonly field can be changed by the containing class using static constructor as shown below.
class Program
{
       // Initialize the static readonly field
       // to an initial value of 100
          public static readonly int Number=100;
          static Program()
          {
               //Value changed to 200 in the static constructor
                 Number = 200;
          }
}

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LINQ Interview Questions Part 2

2010-06-27T05:55:00.000-07:00

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What are the three main components of LINQ or Language INtegrated Query?

1. Standard Query Operators

2. Language Extensions

3. LINQ Providers

How are Standard Query Operators implemented in LINQ?

Standard Query Operators are implemented as extension methods in .NET Framework. These Standard Query Operators can be used to work with any collection of objects that implements the IEnumerable interface. A class that inherits from the IEnumerable interface must provide an enumerator for iterating over a collection of a specific type. All arrays implement IEnumerable. Also, most of the generic collection classes implement IEnumerable interface.

How are Standard Query Operators useful in LINQ?

Standard Query Operators in LINQ can be used for working with collections for any of the following and more.

1. Get total count of elements in a collection.
2. Order the results of a collection.
3. Grouping.
4. Computing average.
5. Joining two collections based on matching keys.
6. Filter the results

List the important language extensions made in C# to make LINQ a reality?
1. Implicitly Typed Variables
2. Anonymous Types
3. Object Initializers
4. Lambda Expressions

What is the purpose of LINQ Providers in LINQ?
LINQ Providers are a set of classes that takes a LINQ query and dynamically generates a method that executes an equivalent query against a specific data source.

What are the four LINQ Providers that .NET Framework ships?
1. LINQ to Objects - Executes a LINQ query against a collection of objects
2. LINQ to XML - Executes an XPATH query against XML documents
3. LINQ to SQL - Executes LINQ queries against Microsoft SQL Server.
4. LINQ to DataSets - Executes LINQ queries against ADO.NET DataSets.

Write a program using LINQ to find the sum of first 5 prime numbers?

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Linq Interview Questions Part 1

2010-06-19T03:37:00.000-07:00

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What is LINQ?
LINQ, or Language INtegrated Query, is a set of classes added to the .NET Framework 3.5. LINQ adds a rich, standardized query syntax to .NET programming languages that allows developers to interact with any type of data.

What are the advantages of using LINQ or Language INtegrated Query?

In any data driven application, you get data either from a Database, or an XML file or from collection classes. Prior to LINQ, working with each data source requires writing a different style of code. Moreover, working with external resources like data bases, XML files involves communicating with that external resource in some syntax specific to that resource. To retrieve data from a database you need to send it a string that contains the SQL query to execute, similarly, to work with an XML document involves specifying an XPath expression in the form of a string. The idea is that using LINQ you can work with disparate data sources using a similar style without having to know a separate syntax for communicating with the data source (e.g., SQL or XPath) and without having to resort to passing opaque strings to external resources.

In any data driven web application or windows application, we use database as a datasource for the application. In order to get data from the database and display it in a web or windows application, we typically do the following.
1. Prepare your SQL Statements.
2. Execute SQL Statements against the database.
3. Retrieve the results.
4. Populate the Business Objects.
5. Display the Data in the Web Form or Windows From.

In order to send a query to the database we must first establish a connection to the database. We then must encode the logic - the SQL query, its parameters, and the parameters' values - into strings that are supplied to the SqlCommand object. And because these inputs are encoded into opaque strings, there is no compile-time error checking and very limited debugging support. For example, if there is a spelling mistake in the SELECT query causing the Customets table name to be misspelled, this typographical error won't show up until runtime when this page is viewed in a web browser. These typographical errors are easy to make as there is no IntelliSense support. When we use LINQ, Visual Studio would display an error message alerting us about the incorrect table name.

Another mismatch between the programming language and the database is that the data returned by the database is transformed for us into objects accessible through the SqlDataReader, but these objects are not strongly-typed objects like we'd like. To get this data into strongly-typed objects we must write code ourselves that enumerates the database results and populates each record into a corresponding object.

LINQ was designed to address all these issues. LINQ also offers a unified syntax for working with data, be it data from a database, an XML file, or a collection of objects. With LINQ you don't need to know the intricacies of SQL, the ins and outs of XPath, or various ways to work with a collection of objects. All you need be familiar with is LINQ's classes and the associated language enhancements centered around LINQ.

In other words, LINQ provides type safety, IntelliSense support, compile-time error checking, and enhanced debugging scenarios when working with different datasources.

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Best pactices in developing asp.net applications - Part 2

2010-01-09T22:56:00.000-08:00

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1. Do not catch general exception types - You should not catch Exception or SystemException. Catching generic exception types can hide run-time problems from the library user, and can complicate debugging. You should catch only those exceptions that you can handle gracefully.

2. Use properties instead of visible instance fields.

3. Follow the same naming conventions accross the solution.

4. Remove unwanted commented code, Indent code properly.

5. Use curly braces with in an if statement, even if there is a single statement in the if block. This will provide better readability.

6. Make sure to refactor your code to move the duplicated code to common reusable functions.

7. Move one time control settings into the .aspx page rather than having them in the code behind in if(!IsPostback) block.

8. Use inheritance whereever possible, which enables code reuse and also reduces the amount of code we have to write and test.

9. Move the reusable javascript functions to an external .js file instead of having them on the page.

10. For controls that are declarativley specified on the page, tie the event handlers to the controls events on the aspx page rather than initializing them in the codebehind. If the controls are built dynamically then we donot have a choice.

11. Make sure to check for nulls when using any type retrieved from a session, querystring or a database to avoid NullReferenceExceptions.

12. Use foreach loop instead of using for loop which may lead to out of boundary run time exceptions.

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Best pactices in developing asp.net applications - Part 1

2010-01-09T22:43:00.000-08:00

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1. Remove unused private fields and functions.

2. Do not cast unnecessarily. Avoid duplicate casts where possible, since there is a cost associated with them.

3. Properties that return arrays are prone to code inefficiencies. Consider using a collection or making this a method.

4. To test for empty strings, check if String.Length is equal to zero. Constructs such as "".Equals(someString) and String.Empty.Equals(someString) are less efficient than testing the string length. Replace these with checks for someString.Length == 0.

5. Methods in the same type that differ only by return type can be difficult for developers and tools to properly recognize. When extending a type, be sure not to define new methods that differ from base type methods only by type.

6. Use stringbuilder instead of string types for string manipulation.

7. Use String.Format instead of concatenating and appending strings.

8. Use Type.TryParse rather than Convert.ToDestinationType(). For example use int.TryParse() rather than Convert.ToInt32() which might throw an exception.

9. Override Equals() method wherever applicable in your classes.

10. Consider passing base types as parameters - Using base types as parameters to methods improves re-use of these methods if you only use methods & properties from the parameter's base class. E.g. use Stream instead of FileStream as a parameter when only calling Stream.Read(), this makes the method work on all kind of streams instead of just File streams.

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ASP.NET Interview Questions on Data Access Security

2009-01-17T17:45:00.000-08:00

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What are the best practices to follow to secure connection strings in an ASP.NET web application?
1. Always store connection strings in the site's Web.config file. Web.config is very secure. Users will not be able to access web.config from the browser.
2. Do not store connection strings as plain text. To help keep the connection to your database server secure, it is recommended that you encrypt connection string information in the configuration file.
3. Never store connection strings in an aspx page.
4. Never set connection strings as declarative properties of the SqlDataSource control or other data source controls.Why is "Connecting to SQL Server using Integrated Security" considered a best practice?Connecting to SQL Server using integrated security instead of using an explicit user name and password, helps avoid the possibility of the connection string being compromised and your user ID and password being exposed.

What is the advantage of storing an XML file in the applications App_Data folder?
The contents of the App_Data folder will not be returned in response to direct HTTP requests.

What is Script injection?
A script injection attack attempts to send executable script to your application with the intent of having other users run it. A typical script injection attack sends script to a page that stores the script in a database, so that another user who views the data inadvertently runs the code.What is SQL injection?A SQL injection attack attempts to compromise your database by creating SQL commands that are executed instead of, or in addition to, the commands that you have built into your application.What are the best practices to keep in mind when accepting user input on a web application?
1. Always use validation controls whenever possible to limit user input to acceptable values.
2. Always check the IsValid property of the aspx page. Run the server side code only if the IsValid property value is true. A value of false means that one or more validation controls have failed a validation check.
3. Always perform server side validation irrespective of client side validation being performed or not. This will protect your web application even if the client has by passed the client side validation by disabling javascript in the web browser.
4. Also make sure to re validate user input in the business logic layer of your application.What are the steps to follow to avoid Script Injection attacks?
1. Encode user input with the HtmlEncode method. This method turns HTML into its text representation.
2. If you are using the GridView control with bound fields, set the BoundField object's HtmlEncode property to true. This causes the GridView control to encode user input when the row is in edit mode.What are the steps to follow to avoid SQL Injection attacks?Always use parameterized queries or stored procedures instead of creating SQL commands by concatenating strings together.

Can you encrypt view state data of an aspx page?
Yes, you encrypt view state data of an aspx page by setting the page's ViewStateEncryptionMode property to true.

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List all the files in a directory on a web form in asp.net

2008-11-26T11:43:00.000-08:00

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Question :
List all the files in a directory on a web form. The files must be displayed in a gridview control. The name of the file and create date must be displayed.

Answer:
1. Create a new web form. Drag and drop a gridview control from the toolbox onto the webform.

2. Create 2 bound fields for the gridview. One bound field will display the file name and the other will display the create date.

3. The HTML for your web form should be as shown below.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ListFiles.aspx.cs" Inherits="ListFiles" %>
<html>
<head runat="server">
<title>List all the files in a directory</title>
</head>
<body>
<form id="form1" runat="server">
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False">
<Columns>
<asp:BoundField DataField="FileName" HeaderText="File Name"></asp:BoundField>
<asp:BoundField DataField="DateCreated" HeaderText="Date" DataFormatString="{0:d}"></asp:BoundField>
</Columns>
</asp:GridView>
</form>
</body>
</html>

4. In the code behind file write a function which can get the list of files from the directory and bind to the gridview. The function is as shown below.
private void LoadFiles()
{
/* Create an instance of DirectoryInfo class for enumarating through the directory. */
System.IO.DirectoryInfo dirInfo = new System.IO.DirectoryInfo(Server.MapPath("FilesDirectory"));
/* Call the GetFiles() instance method of the DirectoryInfo class object, which will return a files list from the current directory */
System.IO.FileInfo[] fiFiles = dirInfo.GetFiles();
/* Create a DataTable which can be used as the datasource for the gridview */
DataTable dtFileList = new DataTable("Files");
/* Create a DataColumn for file name */
DataColumn dcFileName = new DataColumn("FileName");
/* Create a DataColumn for file create date */
DataColumn dcDateCreated = new DataColumn("DateCreated", typeof(DateTime));
/* Add the 2 data columns to the data table */
dtFileList.Columns.Add(dcFileName);
dtFileList.Columns.Add(dcDateCreated);
/* Now loop through each FileInfo object and get the file name and file create date */
foreach (System.IO.FileInfo f in fiFiles)
{
DataRow dtNewRow = dtFileList.NewRow();
/* Get the file name using FileInfo object "Name" property */
dtNewRow["FileName"] = f.Name.ToString();
/* Get the file create date and time using FileInfo object "CreationTime" property */
dtNewRow["DateCreated"] = f.CreationTime.ToShortDateString();
/* Add the row to the DataTable */
dtFileList.Rows.Add(dtNewRow);
}
/* Set the datatable as the DataSource for the gridview and call the DataBind() method */
GridView1.DataSource = dtFileList;
GridView1.DataBind();
}

5. Finally call the LoadFiles() method on the page load event handler as shown below.
protected void Page_Load(object sender, EventArgs e)
{
LoadFiles();
}

Testing the application:
1. Right click on the project name in solution explorer, and left click on "NewFolder"
2. Rename the "NewFolder" to "FilesDirectory"
3. Drag and Drop some files into the directoy.
4. Then run the application. All the files in the "FilesDirectory" folder will be shown in the gridview.

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Write and Read a cookie - ASP.NET Interview Questions

2008-11-26T11:36:00.000-08:00

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Question:Give an example to show how to write and read a cookie from a client's computer.

Answer:
1. The following example shows how to write a "USER" cookie to a client's computer. The "USER" cookie, stores
FirstName
LastName
LastVisit

2. Create the user interface to enter FirstName and LastName. The HTML for the webform is as shown below.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="CookiesExample.aspx.cs" Inherits="CookiesExample" %>
<html>
<head runat="server">
<title>Write a cookie to the client computer</title>
</head>
<body>
<form id="form1" runat="server">
<table>
<tr>
<td style="width: 100px">
First Name</td>
<td style="width: 100px">
<asp:TextBox ID="FirstNameTextBox" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td style="width: 100px">
Last Name
</td>
<td style="width: 100px">
<asp:TextBox ID="LastNameTextBox" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td style="width: 100px">
</td>
<td style="width: 100px">
<asp:Button ID="WriteCookieButton" runat="server" Text="Write Cookie" OnClick="WriteCookieButton_Click" />
</td>
</tr>
<tr>
<td style="width: 100px">
</td>
<td style="width: 100px">
<asp:Button ID="ReadCookieButton" runat="server" Text="Read Cookie" OnClick="ReadCookieButton_Click" />
</td>
</tr>
</table>
</form>
</body>
</html>

3. WriteCookieButton_Click event handler in the code behind file, has the code required to write the cookie to the client computer as shown below.
protected void WriteCookieButton_Click(object sender, EventArgs e)
{
// Create an instance of HttpCookie class
HttpCookie UserCookie = new HttpCookie("USER");
// Populate FirstName, LastName and LastVisit fields
UserCookie["FirstName"] = FirstNameTextBox.Text;
UserCookie["LastName"] = LastNameTextBox.Text;
UserCookie["LastVisit"] = DateTime.Now.ToString();
// Set the cookie expiration date
UserCookie.Expires = DateTime.Now.AddDays(3);
// Write the cookie to the client computer
Response.Cookies.Add(UserCookie);
}

4. ReadCookieButton_Click even handler in the code behind file has the code to read the cookie from the client computer as shown below.
protected void ReadCookieButton_Click(object sender, EventArgs e)
{
// Check if the "USER" cookie exists on the client computer
if (Request.Cookies["USER"] != null)
{
//Retrieve the "USER" cookie into a cookie object
HttpCookie UserCookie = Request.Cookies["USER"];
//Write FirstName,LastName and LastVisit values
Response.Write("First Name = " + UserCookie["FirstName"] + "
");
Response.Write("Last Name = " + UserCookie["LastName"] + "
");
Response.Write("Last Visit = " + UserCookie["LastVisit"] + "
");
}
}

5. Finally test. Run the application and enter first name and Last name and click, the write cookie button. This should write the cookie to the client's computer. Now click the read cookie button, which will read the FirstName, LastName and LastVisit information from the cookie and writes on to the webform.

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ASP.NET Interview Questions on HTTP modules and HTTP Handlers

2008-11-24T16:07:00.000-08:00

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What is an HTTP Handler?
An ASP.NET HTTP handler is the process (frequently referred to as the "endpoint") that runs in response to a request made to an ASP.NET Web application. The most common handler is an ASP.NET page handler that processes .aspx files. When users request an .aspx file, the request is processed by the page through the page handler. You can create your own HTTP handlers that render custom output to the browser.

What is HTTP module?An HTTP module is an assembly that is called on every request that is made to your application. HTTP modules are called as part of the ASP.NET request pipeline and have access to life-cycle events throughout the request. HTTP modules let you examine incoming and outgoing requests and take action based on the request.

What is the interface that you have to implement if you have to create a Custom HTTP Handler?
Implement IHttpHandler interface to create a synchronous handler.
Implement IHttpAsyncHandler to create an asynchronous handler.

What is the difference between asynchronous and synchronous HTTP Handlers?A synchronous handler does not return until it finishes processing the HTTP request for which it is called.

An asynchronous handler runs a process independently of sending a response to the user. Asynchronous handlers are useful when you must start an application process that might be lengthy and the user does not have to wait until it finishes before receiving a response from the server.

Which class is responsible for receiving and forwarding a request to the appropriate HTTP handler?
IHttpHandlerFactory Class

Can you create your own custom HTTP handler factory class?
Yes, we can create a custom HTTP handler factory class by creating a class that implements the IHttpHandlerFactory interface.

What is the use of HTTP modules?
HTTP modules are used to implement various application features, such as forms authentication, caching, session state, and client script services.

What is the difference between HTTP modules and HTTP handlers?An HTTP handler returns a response to a request that is identified by a file name extension or family of file name extensions. In contrast, an HTTP module is invoked for all requests and responses. It subscribes to event notifications in the request pipeline and lets you run code in registered event handlers. The tasks that a module is used for are general to an application and to all requests for resources in the application.

What is the common way to register an HTTP module?The common way to register an HTTP module is to have an entry in the application's Web.config file.

Much of the functionality of a module can be implemented in a global.asax file. When do you create an HTTP module over using Global.asax File?
You create an HTTP module over using Global.asax file if the following conditions are true

1. You want to re-use the module in other applications.
2. You want to avoid putting complex code in the Global.asax file.
3. The module applies to all requests in the pipeline.

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ASP.NET Interview Questions on Themes and Skins

2008-11-22T18:31:00.000-08:00

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What is a "theme" in ASP.NET?
A "theme" is a collection of property settings that allow you to define the look of pages and controls, and then apply the look consistently across pages in a Web application, across an entire Web application, or across all Web applications on a server.

What is the extension for a skin file?
.skin

What are the 2 types of control skins in ASP.NET?
1. Default skins
2. Named skins

What is the difference between Named skins and Default skins?
A default skin automatically applies to all controls of the same type when a theme is applied to a page. A control skin is a default skin if it does not have a SkinID attribute. For example, if you create a default skin for a Calendar control, the control skin applies to all Calendar controls on pages that use the theme. (Default skins are matched exactly by control type, so that a Button control skin applies to all Button controls, but not to LinkButton controls or to controls that derive from the Button object.)

A named skin is a control skin with a SkinID property set. Named skins do not automatically apply to controls by type. Instead, you explicitly apply a named skin to a control by setting the control's SkinID property. Creating named skins allows you to set different skins for different instances of the same control in an application.

What are the 3 levels at which a theme can be applied for a web application?
1. At the page level - Use the Theme or StyleSheetTheme attribute of the @ Page directive.

2. At the application level - Can be applied to all pages in an application by setting the <pages> element in the application configuration file.

3. At the web server level - Define the <pages> element in machine.config file. This will apply the theme to all the web applications on that web server.

What is the name of the folder that contains the application themes?
App_Themes

What is a global theme?
A global theme is a theme that you can apply to all the Web sites on a server. Global themes allow you to define an overall look for your domain when you maintain multiple Web sites on the same server.

What is the difference between themes and CSS?
1. Themes can define many properties of a control or page, not just style properties. For example, using themes, you can specify the graphics for a TreeView control, the template layout of a GridView control, and so on.

2. Themes can include graphics.

3. Themes do not cascade the way style sheets do. By default, any property values defined in a theme referenced by a page's Theme property override the property values declaratively set on a control, unless you explicitly apply the theme using the StyleSheetTheme property.

4. Only one theme can be applied to each page. You cannot apply multiple themes to a page, unlike style sheets where multiple style sheets can be applied.

What are the security concerns to keep in mind when using themes?
Themes can cause security issues when they are used on your Web site. Malicious themes can be used to:

1. Alter a control's behavior so that it does not behave as expected.

2. Inject client-side script, therefore posing a cross-site scripting risk.

3. Expose sensitive information.

4. The mitigations for these common threats are:

5. Protect the global and application theme directories with proper access control settings. Only trusted users should be allowed to write files to the theme directories.

6. Do not use themes from an untrusted source. Always examine any themes from outside your organization for malicious code before using them on you Web site.

7. Do not expose the theme name in query data. Malicious users could use this information to use themes that are unknown to the developer and thereby expose sensitive information.

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Reading and writing to an XML file.

2008-11-22T17:59:00.000-08:00

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Question:
Create a simple web page, that can read and write to an XML file. The XML file has a list of email ids. The sample web form should have the following functionality. You have 30 minutes to code and test.

1. A TextBox to accept a valid email id.

2. A submit button. When you click the submit button, the email id entered in the TextBox must be saved to the XML file.

3. If I donot enter anything in the TextBox and click the submit button, the application should show a validation message stating "Email is required".

4. If I enter an invalid email, the application should show a message "Invalid Email".

5. If javascript is enabled the validation should happen on the client browser without postback. If javascript is disabled the validation should happen on the web server.

6. Finally we should have a list box, which will show all the existing email ids in the XML file. When you submit a new email, the listbox should be reloaded showing the newly added email along with already existing email ids.

Answer:
1. Create a webform and add a TextBox, RequiredFieldValidator, RegularExpressionValidator, Button and a ListBox.

2. Set the RequiredFieldValidator "ErrorMessage" property to "Email Required" and "ControlToValidate" property to "EmailTextBox" and "Display" property to "Dynamic" as shown below.
<asp:RequiredFieldValidator ID="EmailRequiredFieldValidator" runat="server" ErrorMessage="Email Required" ControlToValidate="EmailTextBox" Display="Dynamic"></asp:RequiredFieldValidator>

3. Set the RegularExpressionValidator "ErrorMessage" property to "Invalid Email" and "ControlToValidate" property to "EmailTextBox" and "Display" property to "Dynamic" as shown below.
<asp:RegularExpressionValidator ID="EmailRegularExpressionValidator" runat="server" ErrorMessage="Invalid Email" ControlToValidate="EmailTextBox" Display="Dynamic" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"></asp:RegularExpressionValidator>

4. Set the ListBox, "DataTextField" property to "Email" and DataValueField property to "Email"

5. The complete HTML of the web form should be as shown below.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<html>
<head runat="server">
<title>Email List</title>
</head>
<body>
<form id="form1" runat="server">
<table>
<tr>
<td>
Please enter a valid email:
</td>
<td>
<asp:TextBox ID="EmailTextBox" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="EmailRequiredFieldValidator" runat="server" ErrorMessage="Email Required" ControlToValidate="EmailTextBox" Display="Dynamic"></asp:RequiredFieldValidator>
<asp:RegularExpressionValidator ID="EmailRegularExpressionValidator" runat="server" ErrorMessage="Invalid Email" ControlToValidate="EmailTextBox" Display="Dynamic" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"></asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
</td>
<td>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Submit" /></td>
</tr>
</table>
<br />
Existing Email Ids
<br />
<asp:ListBox ID="ListBox1" runat="server" Height="292px" Width="192px" DataTextField="Email" DataValueField="Email"></asp:ListBox>
</form>
</body>
</html>

6. Place the XML file that contains the list of email ids in the root folder of the web application. The sample XML file is shown below.
<?xml version="1.0" standalone="yes"?>
<EmailsList>
<Emails>
<Email>dhex@yahoo.com</Email>
</Emails>
<Emails>
<Email>dmexy@aol.com</Email>
</Emails>
<Emails>
<Email>dpitt@gmail.com</Email>
</Emails>
<Emails>
<Email>mston@microsoft.com</Email>
</Emails>
</EmailsList>

7. In the code behind file, write a function the can read the email ids from the XML file into a DataSet. Set this DataSet as the DataSource for the ListBox and call the DataBind() method. The function should be as shown below.
private void LoadExistingEmails()
{
DataSet DS = new DataSet();
DS.ReadXml(Server.MapPath("Emails.xml"));

ListBox1.DataSource = DS;
ListBox1.DataBind();
}

8. Call the above LoadExistingEmails() function in the Page_Load event handler as shown in the sample code below.
protected void Page_Load(object sender, EventArgs e)
{
LoadExistingEmails();
}

9. Finally, when you click the submit button write to the XML file as shown below.
protected void Button1_Click(object sender, EventArgs e)
{
if (Page.IsValid)
{
DataSet DS = new DataSet();
DS.ReadXml(Server.MapPath("Emails.xml"));

DataRow DR = DS.Tables[0].NewRow();
DR["Email"] = EmailTextBox.Text;

DS.Tables[0].Rows.Add(DR);

DS.WriteXml(Server.MapPath("Emails.xml"));
LoadExistingEmails();
}
}

Points to remember:
1. Validation controls work both on the client and on the server.

2. If javascript is enabled validations happen on the client browser without posting the page back to the server.

3. If javascript is disabled, validations happen on the server. To check if all the validation controls haved passed validation, use Page.IsValid property.

4. Page.IsValid returns "true" if the page has succeeded validation and "false" even if a single validation control has filed validation.

5. In our example, we write to the XML file only if Page.IsValid property returns true.

Testing the sample application:
To test if the validation controls are working on the server, disable javascript on the client browser. To disable javascript on the client browser follow the below steps.
1. Open internet explorer.

2. Click on Tools.

3. Click on Internet Options. You will see Internet Options dialog page.

4. Click on the Security tab.

5. On the Security tab, select Local intranet under Select a zone to view or change security settings.

6. Click "Custom Level" button under "Security Level for this zone"

7. On the "Security Setting - Local Intranet Zone" dialog page, scroll down to "Scripting" section.

8. Select "Disable" radio button under "Active scription" and click "OK" button.

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write a custom reusable function to populate a dropdownlist

2008-11-20T16:28:00.000-08:00

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Write a custom function in c-sharp. The custom function parameters should be an instance of a dropdownlist, an xml file and a string.
1. The function should be capabale of populating the passed in dropdownlist.
2. The first item in the dropdownlist should be the passed in string parameter.
3. The data for the dropdownlist comes from the passed in XML file.

The idea is to create a custom function which can be reused through out the project for populating any dropdownlist on any web page. You have 20 minutes to code, test and demonstrate.

The sample code for custom function is shown below. For this example to work drop the XML file in the root folder of the web application.

protected void Page_Load(object sender, EventArgs e)
{
PopulateDropdownlist(DropDownList1, "DropDownListSource.xml", "Select State");
}

public void PopulateDropdownlist(System.Web.UI.WebControls.DropDownList DropDownListObjectToBePopulated,string XMLFilePath, string InitialString)
{
try
{
DataSet DS = new DataSet();
DS.ReadXml(Server.MapPath(XMLFilePath));
if (InitialString != string.Empty)
{
ListItem LI = new ListItem(InitialString, "-1");
DropDownListObjectToBePopulated.Items.Add(LI);
}
foreach (DataRow DR in DS.Tables["State"].Rows)
{
ListItem LI = new ListItem();
LI.Text = DR["StateName"].ToString();
LI.Value = DR["StateCode"].ToString();
DropDownListObjectToBePopulated.Items.Add(LI);
}
}
catch(Exception Ex)
{
}
}

The XML file that has the data for the dropdownlist is as shown below.

<?xml version="1.0" encoding="utf-8" ?>
<StatesList>
<State>
<StateName>Virginia</StateName>
<StateCode>VA</StateCode>
</State>
<State>
<StateName>Iowa</StateName>
<StateCode>IA</StateCode>
</State>
<State>
<StateName>North Carolina</StateName>
<StateCode>NC</StateCode>
</State>
<State>
<StateName>Pennsylvania</StateName>
<StateCode>PA</StateCode>
</State>
<State>
<StateName>Texas</StateName>
<StateCode>TX</StateCode>
</State>
</StatesList>

Explanation of the code:
1. PopulateDropdownlist function has 3 parameters. DropDownList to be populated, the path of the XML file which has the data for the dropdownlist and the initial string.

2. Create an instance of DataSet. In our example the instance is DS.
DataSet DS = new DataSet();

3. Read the XML data into the dataset instance using ReadXml() method. Pass the path of the XML file to ReadXml() method. We used Server.MapPath() method to return the physical file path that corresponds to the specified virtual path on the web server.
DS.ReadXml(Server.MapPath(XMLFilePath));

4. We now have the data from the XML file in the dataset as a DataTable.

5. Check if the InitialString is empty. If not empty create a new ListItem object and populate the Text and Value properties. Then add the listitem object to the dropdownlist.
if (InitialString != string.Empty)
{
ListItem LI = new ListItem(InitialString, "-1");
DropDownListObjectToBePopulated.Items.Add(LI);
}

6. Finally loop thru the rows in the DataTable and create an instance of ListItem class. Populate the Text and Value properties to StateName and StateCode respectively. Finally add the ListItem object to the dropdownlist.
foreach (DataRow DR in DS.Tables["State"].Rows)
{
ListItem LI = new ListItem();
LI.Text = DR["StateName"].ToString();
LI.Value = DR["StateCode"].ToString();
DropDownListObjectToBePopulated.Items.Add(LI);
}

7. Drag and drop the dropdownlist on a webform. Call the PopulateDropdownlist() custom function in the Page_Load event handler. When you call the custom function pass the dropdownlist to be populated, XML file path and the initial string.
protected void Page_Load(object sender, EventArgs e)
{
PopulateDropdownlist(DropDownList1, "DropDownListSource.xml", "Select State");
}

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ASP.NET Interview Questions on DataSet

2008-11-19T15:25:00.000-08:00

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What is a DataSet?
DataSet is an in-memory cache of data.

In which namespace is the DataSet class present?
System.Data

Can you add more than one table to a dataset?
Yes

Can you enforce constarints and relations on tables inside a DataSet?
Yes, the DataSet consists of a collection of DataTable objects that you can relate to each other with DataRelation objects. You can also enforce data integrity in the DataSet by using the UniqueConstraint and ForeignKeyConstraint objects.

What happens when you invoke AcceptChanges() method on a DataSet?
Invoking AcceptChanges() method on the DataSet causes AcceptChanges() method to be called on each table within the DataSet.

Both the DataRow and DataTable classes also have AcceptChanges() methods. Calling AcceptChanges() at the DataTable level causes the AcceptChanges method for each DataRow to be called.

When you call AcceptChanges on the DataSet, any DataRow objects still in edit-mode end their edits successfully. The RowState property of each DataRow also changes. Added and Modified rows become Unchanged, and Deleted rows are removed.

If the DataSet contains ForeignKeyConstraint objects, invoking the AcceptChanges method also causes the AcceptRejectRule to be enforced.

Is there a way to clear all the rows from all the tables in a DataSet at once?
Yes, use the DataSet.Clear() method to clear all the rows from all the tables in a DataSet at once.

What is the difference between DataSet.Copy() and DataSet.Clone()?
DataSet.Clone() copies the structure of the DataSet, including all DataTable schemas, relations, and constraints. Does not copy any data.

DataSet.Copy() copies both the structure and data.

How do you get a copy of the DataSet containing all changes made to it since it was last loaded?
Use DataSet.GetChanges() method

What is the use of DataSet.HasChanges() Method?
DataSet.HasChanges method returns a boolean true if there are any changes made to the DataSet, including new, deleted, or modified rows. This method can be used to update a DataSource only if there are any changes.

How do you roll back all the changes made to a DataSet since it was created?
Invoke the DataSet.RejectChanges() method to undo or roll back all the changes made to a DataSet since it was created.

What happnes when you invoke RejectChanges method, on a DataSet that contains 3 tables in it?
RejectChanges() method will be automatically invoked on all the 3 tables in the dataset and any changes that were done will be rolled back for all the 3 tables.

When the DataTable.RejectChanges method is called, any rows that are still in edit-mode cancel their edits. New rows are removed. Modified and deleted rows return back to their original state. The DataRowState for all the modified and deleted rows will be flipped back to unchanged.

What is the DataSet.CaseSensitive property used for?
When you set the CaseSensitive property of a DataSet to true, string comparisons for all the DataTables within dataset will be case sensitive. By default the CaseSensitive property is false.

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ASP.NET Interview Questions on Globalization

2008-11-17T16:41:00.000-08:00

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What is Globalization?
Globalization is the process of creating an application that meets the needs of users from multiple cultures. This process involves translating the user interface elements of an application into multiple languages, using the correct currency, date and time format, calendar, writing direction, sorting rules, and other issues. Accommodating these cultural differences in an application is called localization.

The Microsoft .NET Framework simplifies localization tasks substantially by making its formatting, date/time, sorting, and other classes culturally aware. Using classes from the System.Globalization namespace, you can set the application’s current culture, and much of the work is done automatically!

What are the 3 different ways to globalize web applications?

Detect and redirect approach : In this approach we create a separate Web application for each supported culture, and then detect the user’s culture and redirect the request to the appropriate application. This approach is best for applications with lots of text content that requires translation and few executable components.

Run-time adjustment approach : In this approach we create a single Web application that detects the user’s culture and adjusts output at run time using format specifiers and other tools. This approach is best for simple applications that present limited amounts of content.

Satellite assemblies approach : In this approach we create a single Web application that stores culture-dependent strings in resource files that are compiled into satellite assemblies. At run time, detect the user’s culture and load strings from the appropriate assembly. This approach is best for applications that generate content at run time or that have large executable components.

In ASP.NET, how do you detect the user's language preference on his/her computer?
Use the Request object’s UserLanguages property to return a list of the user’s language preferences. The first element of the array returned by UserLanguages is the user’s current language on his/her computer.

What are the steps to follow to get user's culture at run time?
To get the user’s culture at run time, follow these steps:
1. Get the Request object’s UserLanguages property.
2. Use the returned value with the CultureInfo class to create an object representing the user’s current culture.

For example, the following code gets the user’s culture and displays the English name and the abbreviated name of the culture in a label the first time the page is displayed:
private void Page_Load(object sender, System.EventArgs e)
{
// Run the first time the page is displayed
if (!IsPostBack)
{
// Get the user's preferred language.
string sLang = Request.UserLanguages[0];
// Create a CultureInfo object from it.
CultureInfo CurrentCulture = new CultureInfo(sLang);
lblCulture.Text = CurrentCulture.EnglishName + ": " +
CurrentCulture.Name;
}
}

What are the advantages of using detect and redirect approach to globalizing web applications?
1. Content is maintained separately, so this approach allows the different applications to present very different information, if needed.
2. Users can be automatically directed to sites that are likely to be geographically close, and so can better meet their needs.
3. Content files (Web forms and HTML pages, for example) can be authored in the appropriate natural language without the complexity of including resource strings.

What are the disadvantages of using detect and redirect approach to globalizing web applications?
1. Using this approach requires that the executable portion of the Web application be compiled and deployed separately to each culture-specific Web site.
2. This approach requires more effort to maintain consistency and to debug problems across Web sites.

What is the use of culture attribute of the globalization element in web.config?
The Web.config file’s globalization element is used to create a culture-specific Web application. The culture attribute of the globalization element specifies how the Web application deals with various culture-dependent issues, such as dates, currency, and number formatting.

Web.config globalization settings in subordinate folders override the globalization settings in the application’s root Web.config file. You can store content for various cultures in subfolders within your application, add Web.config files with the globalization settings for each culture, then direct users to the appropriate folder based on the user’s CurrentCulture.

The text on the webform is usually written from left to right. How do you change the writing direction to "right to left"?
The wrting direction of a webform can be changed using the HTML dir attribute as shown below.
<body dir="rtl">

You can use the dir attribute individually in panels, text boxes, or other controls as well. Setting the dir attribute on the body element applies right-to-left formatting to the entire page.

What do you mean by neutral cultures?
Neutral cultures represent general languages, such as English or Spanish, rather than a specific language and region. When you set the culture attribute for a Web application in Web.config, ASP.NET assigns that culture to all the threads running for that Web application. Threads are the basic unit to which the server allocates processor time. ASP.NET maintains multiple threads for a Web application within the aspnet_wp.exe worker process.

What are advantages of setting the culture dynamically at the thread level over creating separate Web applications for each culture?
1. All cultures share the same application code, so the application doesn’t have to be compiled and deployed for each culture.
2. The application resides at a single Web address, you don’t need to redirect users to other Web applications.
3. The user can choose from a full array of available cultures.

For what type of web applications setting the culture dynamically is best suited?
Setting the culture dynamically is best suited for simple Web applications that don’t contain large amounts of text that must be translated into different languages.

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C# Interview Questions - Arrays

2008-11-13T20:09:00.000-08:00

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What is the difference between arrays in C# and arrays in other programming languages?
Arrays in C# work similarly to how arrays work in most other popular languages There are, however, a few differences as listed below

1. When declaring an array in C#, the square brackets ([]) must come after the type, not the identifier. Placing the brackets after the identifier is not legal syntax in C#.

int[] IntegerArray; // not int IntegerArray[];

2. Another difference is that the size of the array is not part of its type as it is in the C language. This allows you to declare an array and assign any array of int objects to it, regardless of the array's length.

int[] IntegerArray; // declare IntegerArray as an int array of any size
IntegerArray = new int[10]; // IntegerArray is a 10 element array
IntegerArray = new int[50]; // now IntegerArray is a 50 element array

What are the 3 different types of arrays that we have in C#?
1. Single Dimensional Arrays
2. Multi Dimensional Arrays also called as rectangular arrays
3. Array Of Arrays also called as jagged arrays

Are arrays in C# value types or reference types?
Reference types.

What is the base class for all arrays in C#?
System.Array

How do you sort an array in C#?
The Sort static method of the Array class can be used to sort array items.

Give an example to print the numbers in the array in descending order?
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int[] Numbers = { 2, 5, 3, 1, 4 };
//Print the numbers in the array without sorting
Console.WriteLine("Printing the numbers in the array without sorting");
foreach (int i in Numbers)
{
Console.WriteLine(i);
}
//Sort and then print the numbers in the array
Console.WriteLine("Printing the numbers in the array after sorting");
Array.Sort(Numbers);
foreach (int i in Numbers)
{
Console.WriteLine(i);
}
//Print the numbers in the array in desceding order
Console.WriteLine("Printing the numbers in the array in desceding order");
Array.Reverse(Numbers);
foreach (int i in Numbers)
{
Console.WriteLine(i);
}
}
}
}

What property of an array object can be used to get the total number of elements in an array?
Length property of array object gives you the total number of elements in an array. An example is shown below.
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int[] Numbers = { 2, 5, 3, 1, 4 };
Console.WriteLine("Total number of elements = " +Numbers.Length);
}
}
}

Give an example to show how to copy one array into another array?
We can use CopyTo() method to copy one array into another array. An example is shown below.
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int[] Numbers = { 2, 5, 3, 1, 4 };
int[] CopyOfNumbers=new int[5];
Numbers.CopyTo(CopyOfNumbers,0);
foreach (int i in CopyOfNumbers)
{
Console.WriteLine(i);
}
}
}
}

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XML Interview Questions - Validating XML documents

2008-11-12T17:39:00.000-08:00

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What determines the validity of an XML document?
Document Type Definition(DTD) or an XML Schema determines the validity of an XML document.

What is a valid XML document?
XML documents are compared to rules that are specified in a DTD or schema. A well-formed XML document that meets all of the requirements of one or more specifications is called a valid XML Document.

What are the 2 types of XML parsers?
Nonvalidating Parsers - Parsers that don’t support validation
Validating Parsers - Parsers that support validation

Can you combine both Schema and DTD references in a single XML document?
Yes

Are DTD's well-formed XML documents?
No, DTDs are not well-formed XML documents. This is because they follow DTD syntax rules rather than XML document syntax.

Are XML schema's well-formed XML documents?
Yes.

What is the difference between an XML schema and a DTD?
The XML Schema is the officially sanctioned Schema definition. Unlike DTDs, the format of XML Schemas follows the rules of well-formed XML documents. The Schema also allows for much more granular control over the data that is being described. Because of the XML format and the detailed format controls, Schemas tend to be very complex and often much longer than the XML documents that they are describing. Schemas are often much more easy for developers to read and follow,due to the less cryptic nature of the references in Schemas versus DTDs.

How do you define references to schemas in an XML document?
References to schemas are defined by creating an instance of the XMLSchemainstance namespace. An example is shown below.
<rootelement xmlns:xsi=”http://www.w3.org/2001/XMLSchemainstance” xsi:noNamespaceSchemaLocation=”schemafile.xsd”>

The namespace declaration reference to http://www.w3.org/2001/XMLSchemainstance resolves to an actual document at that location, which is a brief description of the way that the W3C Schema should be referenced. The noNamespaceSchemaLocation value tells us that there is no predefined namespace for the Schema. This means that all of the elements in the XML document should be validated against the schema specified. The location of the Schema is schemafile.xsd. Because there is no path defined, the file containing the schema should be located in the same directory as the XML file to be validated by the Schema.

You can also define the schema location, and map it to a specific namespace by using the schemaLocation attribute declaration instead of noNamespace SchemaLocation. If you do so, you have to declare a namespace that matches the schemaLocation attribute value. The declaration must be made before you reference the schema in a schemaLocation attribute assignment.

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