ASP.NET 2.0 Page Event Life Cycle

In this article, we will explore the various events that occur when an asp.net 2.0 page is requested from the server. Before exploring that, let us briefly take a look at the various components that participate in the request and response model for asp.net pages.
When a request is made to the server using HTTP (GET), IIS receives the request and passes it to the asp.net engine(dll) that compiles the page that is requested. The request passes through two sections :
Http Module – Monitors the request and takes action. Authentication and Authorization take place over here.
Http Handler – Responsible for compiling the page and generating output using System.Web.UI.PageHandlerFactory (we are considering .aspx page for this article).
Once compilation is done, the page is sent back to the Http module which then sends it to the IIS and back to the browser.
The events occur in the following sequence. Its best to turn on tracing(<% @Page Trace=”true”%>) and track the flow of events :
PreInit – This event represents the entry point of the page life cycle. If you need to change the Master page or theme programmatically, then this would be the event to do so. Dynamic controls are created in this event.
Init – Each control in the control collection is initialized.
Init Complete* - Page is initialized and the process is completed.
PreLoad* - This event is called before the loading of the page is completed.
Load – This event is raised for the Page and then all child controls. The controls properties and view state can be accessed at this stage. This event indicates that the controls have been fully loaded.
LoadComplete* - This event signals indicates that the page has been loaded in the memory. It also marks the beginning of the rendering stage.
PreRender – If you need to make any final updates to the contents of the controls or the page, then use this event. It first fires for the page and then for all the controls.
PreRenderComplete* - Is called to explicitly state that the PreRender phase is completed.
SaveStateComplete* - In this event, the current state of the control is completely saved to the ViewState.
Unload – This event is typically used for closing files and database connections. At times, it is also used for logging some wrap-up tasks.

Global.asax file in ASP.NET

The Global.asax, also known as the ASP.NET application file, is located in the root directory of an ASP.NET application. This file contains code that is executed in response to application-level and session-level events raised by ASP.NET or by HTTP modules. You can also define ‘objects’ with application-wide or session-wide scope in the Global.asax file. These events and objects declared in the Global.asax are applied to all resources in that web application.
Note 1: The Global.asax is an optional file. Use it only when there is a need for it.
Note 2: If a user requests the Global.asax file, the request is rejected. External users cannot view the file.
The Global.asax file is parsed and dynamically compiled by ASP.NET. You can deploy this file as an assembly in the \bin directory of an ASP.NET application.
How to create Global.asax
Adding a Global.asax to your web project is quiet simple.
Open Visual Studio 2005 or 2008 > Create a new website > Go to the Solution Explorer > Add New Item > Global Application Class > Add.
Examining the methods related to the events in Global.asax
There are 2 ‘set’ of methods that fire corresponding to the events. The first set which gets invoked on each request and the second set which does not get invoked on each request. Let us explore these methods.
Methods corresponding to events that fire on each request
Application_BeginRequest() – fired when a request for the web application comes in.
Application_AuthenticateRequest –fired just before the user credentials are authenticated. You can specify your own authentication logic over here.
Application_AuthorizeRequest() – fired on successful authentication of user’s credentials. You can use this method to give authorization rights to user.
Application_ResolveRequestCache() – fired on successful completion of an authorization request.
Application_AcquireRequestState() – fired just before the session state is retrieved for the current request.
Application_PreRequestHandlerExecute() - fired before the page framework begins before executing an event handler to handle the request.
Application_PostRequestHandlerExecute() – fired after HTTP handler has executed the request.
Application_ReleaseRequestState() – fired before current state data kept in the session collection is serialized.
Application_UpdateRequestCache() – fired before information is added to output cache of the page.
Application_EndRequest() – fired at the end of each request
Methods corresponding to events that do not fire on each request
Application_Start() – fired when the first resource is requested from the web server and the web application starts.
Session_Start() – fired when session starts on each new user requesting a page.
Application_Error() – fired when an error occurs.
Session_End() – fired when the session of a user ends.
Application_End() – fired when the web application ends.
Application_Disposed() - fired when the web application is destroyed.
Example!!
Let us see an example of how to use the Global.asax to catch unhandled errors that occur at the application level.
To catch unhandled errors, do the following. Add a Global.asax file (Right click project > Add New Item > Global.asax). In the Application_Error() method, add the following code:

C#
void Application_Error(object sender, EventArgs e)
{
// Code that runs when an unhandled error occurs
Exception objErr = Server.GetLastError().GetBaseException();
string err = "Error in: " + Request.Url.ToString() +
". Error Message:" + objErr.Message.ToString();

}
VB.NET
Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs when an unhandled error occurs
Dim objErr As Exception = Server.GetLastError().GetBaseException()
Dim err As String = "Error in: " & Request.Url.ToString() & ". Error Message:" & objErr.Message.ToString()

End Sub
Here we make use of the Application_Error() method to capture the error using the Server.GetLastError().
Conclusion:
In this article, we learnt that Global.asax is a file used to declare application-level events and objects. The file is responsible for handling higher-level application events such as Application_Start, Application_End, Session_Start, Session_End, and so on. I would encourage you to explore the methods corresponding to the events and analyze the best possible methods to use them in your application, if needed.
I hope you liked the article and I thank you for viewing it.

New features in SQL Server 2005

1. T-SQL (Transaction SQL) enhancements
T-SQL is the native set-based RDBMS programming language offering high-performance data access. It now incorporates many new features including error handling via the TRY and CATCH paradigm, Common Table Expressions (CTEs), which return a record set in a statement, and the ability to shift columns to rows and vice versa with the PIVOT and UNPIVOT commands.

2. CLR (Common Language Runtime)
The next major enhancement in SQL Server 2005 is the integration of a .NET compliant language such as C#, ASP.NET or VB.NET to build objects (stored procedures, triggers, functions, etc.). This enables you to execute .NET code in the DBMS to take advantage of the .NET functionality. It is expected to replace extended stored procedures in the SQL Server 2000 environment as well as expand the traditional relational engine capabilities.

3. Service Broker
The Service Broker handles messaging between a sender and receiver in a loosely coupled manner. A message is sent, processed and responded to, completing the transaction. This greatly expands the capabilities of data-driven applications to meet workflow or custom business needs.

4. Data encryption
SQL Server 2000 had no documented or publicly supported functions to encrypt data in a table natively. Organizations had to rely on third-party products to address this need. SQL Server 2005 has native capabilities to support encryption of data stored in user-defined databases.

5. More information from Microsoft.
SMTP mail
Sending mail directly from SQL Server 2000 is possible, but challenging. With SQL Server 2005, Microsoft incorporates SMTP mail to improve the native mail capabilities. Say "see-ya" to Outlook on SQL Server!

6. HTTP endpoints
You can easily create HTTP endpoints via a simple T-SQL statement exposing an object that can be accessed over the Internet. This allows a simple object to be called across the Internet for the needed data.
.
7. Multiple Active Result Sets (MARS)
MARS allow a persistent database connection from a single client to have more than one active request per connection. This should be a major performance improvement, allowing developers to give users new capabilities when working with SQL Server. For example, it allows multiple searches, or a search and data entry. The bottom line is that one client connection can have multiple active processes simultaneously.

8. Dedicated administrator connection
If all else fails, stop the SQL Server service or push the power button. That mentality is finished with the dedicated administrator connection. This functionality will allow a DBA to make a single diagnostic connection to SQL Server even if the server is having an issue.

9. More information from Microsoft.
SQL Server Integration Services (SSIS)
SSIS has replaced DTS (Data Transformation Services) as the primary ETL (Extraction, Transformation and Loading) tool and ships with SQL Server free of charge. This tool, completely rewritten since SQL Server 2000, now has a great deal of flexibility to address complex data movement.

10. Database mirroring
It's not expected to be released with SQL Server 2005 at the RTM in November, but I think this feature has great potential. Database mirroring is an extension of the native high-availability capabilities. So, stay tuned for more details…. For now, here's

Two technologies that cannot be left out of any SQL Server 2005 top 10 list are Analysis Services and Reporting Services. Although neither technology will be introduced with SQL Server 2005, combining them with SQL Server Integration Services rounds off Microsoft's core business intelligence suite. These technologies are essential to business intelligence success. Learn about the new functionality and how organizations are implementing it with Project Real.

SQL Server 2005 Tips and Tricks

Exception Handling in SQL Server 2005
Structured exception handing provides a powerful mechanism for controlling complex programs that have many dynamic runtime characteristics
The TRY block contains transactional code that could potentially fail, while the CATCH block contains code that executes if an error occurs in the TRY block. If any errors occur in the TRY block, execution is diverted to the CATCH block and the error can be handled while error functions can be used to provide the detailed error information. TRY…CATCH has the following abbreviated syntax:

BEGIN TRY
RAISERROR ('Houston, we have a problem', 16,1)
END TRY

BEGIN CATCH
SELECT ERROR_NUMBER() as ERROR_NUMBER,
ERROR_SEVERITY() as ERROR_SEVERITY,
ERROR_STATE() as ERROR_STATE,
ERROR_MESSAGE() as ERROR_MESSAGE
END CATCH

Notice the use of functions in the script above that we are able to use in place of local and/or global variables. These functions should only be used in a CATCH BLOCK and are explained below:

ERROR_NUMBER() returns the number of the error.
ERROR_SEVERITY() returns the severity.
ERROR_STATE() returns the error state number.
ERROR_PROCEDURE() returns the name of the stored procedure or trigger where the error occurred.
ERROR_LINE() returns the line number inside the routine that caused the error.
ERROR_MESSAGE() returns the complete text of the error message. The text includes the values supplied for any substitutable parameters, such as lengths, object names or times.




Check if a database or table exists using Sql Server 2005
The Object_ID() function in SQL Server can be utilised in a number of ways. One such utility is to verify if an object exists.

The Object_ID() takes in the object name and object type as parameters. The object name is the object used and the object type is the type of object used in a schema.

For example to check if a table exists in a database, use this query :

IF OBJECT_ID ('AdventureWorks.dbo.AWBuildVersion','U') IS NOT NULL
Print 'Table Exists'
ELSE
Print 'Table Does Not Exists'

where 'AdventureWorks.dbo.AWBuildVersion' is the object name and 'U' is the object type which represents a table

Similarly you can check for a stored procedure or a view by specifying the correct object type. You can get an entire list of object types over here.

To check if a database exists, you can use the DB_ID() function as shown below :

IF db_id('AdventureWorks') IS NOT NULL
Print 'Database Exists'
ELSE
Print 'Database Does Not Exists'
Display the size of all tables in Sql Server 2005
sp_spaceused returns number of rows, disk space reserved, and disk space used by a table. However when you have to return the space used by all the tables in a database, you have two options: One is to loop through all the tables and then pass the table name to the sp_spaceused procedure. The second is to use the undocumented sp_MSforeachtable procedure. We will explore both of these over here:

The Lengthy Way


USE yourdbname
DECLARE @TblNames Table
(
COUNTER INT IDENTITY(1,1),
tbl_name nvarchar(100) NULL
)
DECLARE @ROWCOUNT INT
DECLARE @I INT
DECLARE @str nvarchar(100)
SET @I = 1
INSERT INTO @TblNames(tbl_name) SELECT name FROM sys.Tables
SET @ROWCOUNT = @@ROWCOUNT
WHILE @I <= @ROWCOUNT
BEGIN
SELECT @str = tbl_name FROM @TblNames WHERE COUNTER = @I
EXEC sp_spaceused @str
SET @I = @I +1
END

Note: The advantage in taking the lengthy approach is that you can create another temporary table and sort the tables based on the space used.

The Short Way

USE yourdbname
EXEC sp_MSforeachtable @command1="EXEC sp_spaceused '?'"

Note: sp_MSforeachtable is an undocumented stored procedure

References :
http://msdn2.microsoft.com/en-us/library/ms188776.aspx
http://www.msnewsgroups.net/group/microsoft.public.dotnet.languages.csharp/topic37975.aspx
http://www.mssqlcity.com/Articles/Undoc/SQL2000UndocSP.htm

Execute a T-SQL statement at a given time
The 'WAITFOR' command is used to delay the execution of a batch, stored procedure or transaction till a specified time duration or till an actual time. Let me demonstrate this:

Create a DELAY for a specific amount of time

USE NORTHWIND
WAITFOR DELAY '00:01:00'
BEGIN
SELECT CustomerID, CompanyName, ContactName FROM CUSTOMERS
END

Delays the execution of the T-Sql statement by 1 minute. To delay by an hour, you would use '01:00:00'. You can specify a maximum of 24 hours.

Execute at the given time (actual time)

USE NORTHWIND
WAITFOR TIME '11:23:00'
BEGIN
SELECT CustomerID, CompanyName, ContactName FROM CUSTOMERS
END

Delays the execution of the T-Sql statement till the time '11:23 A.M'. You cannot specify a date, only time is allowed.

What is new in ASP.NET 3.5

Microsoft released ASP.NET 3.5 on November 19, 2007. Along with it, was released Visual Studio 2008. This evolution from ASP.NET 2.0 to ASP.NET 3.5 is quiet gradual. ASP.NET 3.5 uses the same engine as that of ASP.NET 2.0, with some extra features added on top of it. In this article, we will explore the new features added to ASP.NET 3.5. This article assumes that you have been working on ASP.NET 2.0.
New Features in ASP.NET 3.5

ASP.NET AJAX
In ASP.NET 2.0, ASP.NET AJAX was used as an extension to it. You had to download the extensions and install it. However in ASP.NET 3.5, ASP.NET AJAX is integrated into the .NET Framework, thereby making the process of building cool user interfaces easier and intuitive.
The integration between webparts and the update panel is much smoother. Another noticeable feature is that you can now add ASP.NET AJAX Control Extenders to the toolbox in VS2008. Even though this is an IDE specific feature, however I feel it deserves a mention over here for developers, who had to add extenders using source view earlier. It is also worth noting that Windows Communication Foundation (WCF) now supports JSON along with other standard protocols like SOAP, RSS and POX.
New Controls
The ListView and DataPager are new controls added along with a new datasource control called the LinqDataSource.
ListView
The ListView control is quiet flexible and contains features of the Gridview, Datagrid, Repeater and similar list controls available in ASP.NET 2.0. It provides the ability to insert, delete, page (using Data Pager), sort and edit data. However one feature of the ListView control that stands apart, is that it gives you a great amount of flexibility over the markup generated. So you have a complete control on how the data is to be displayed. You can now render your data without using the tag. You also get a rich set of templates with the ListView control.
DataPager
DataPager provides paging support to the ListView control. The best advantage is that you need not have to keep it ‘tied’ with the control on which the paging is being done. You can keep it anywhere on the page.
DataPager gives you a consistent way of paging with the controls that support it. Currently only ListView supports it as it implements the IPageableItemContainer. However support is likely to be added to other List controls as well.
LINQ
LINQ (Language Integrated Query) adds native data querying capability to C# and VB.NET along with the compiler and Intellisense support. LINQ is a component of .NET 3.5. LINQ defines operators that allow you to code your query in a consistent manner over databases, objects and XML. The ASP.NET LinqDataSource control allows you to use LINQ to filter, order and group data before binding to the List controls.
You can learn more about LINQ over here.
ASP.NET Merge Tool
ASP.NET 3.5 includes a new merge tool (aspnet_merge.exe). This tool lets you combine and manage assemblies created by aspnet_compiler.exe. This tool was available earlier as an add-on.
New Assemblies
The new assemblies that would be of use to ASP.NET 3.5 developers are as follows:
· System.Core.dll - Includes the implementation for LINQ to Objects
· System.Data.Linq.dll - Includes the implementation for LINQ to SQL
· System.Xml.Linq.dll - Includes the implementation for LINQ to XML
· System.Data.DataSetExtensions.dll - Includes the implementation for LINQ to DataSet
· System.Web.Extensions.dll: Includes the implementation for ASP.NET AJAX (new enhancements added) and new web controls as explained earlier.
Other Important Points
1. ASP.NET 3.5 provides better support to IIS7. IIS7 and ASP.NET 3.5 modules and handlers support unified configuration.
2. You can have multiple versions of ASP.NET on the same machine.
3. For those who are wondering what happened to ASP.NET 3.0, well there isn’t anything called ASP.NET 3.0.
4. VS 2002 worked with ASP.NET 1.0, VS 2003 worked with ASP.NET 1.1, and VS 2005 worked with ASP.NET 2.0. However VS 2008 supports multi-targeting, i.e it works with ASP.NET 2.0, and ASP.NET 3.5.

Save and Retrieve Images from the Database using ASP.NET 2.0 and ASP.NET 3.5

At some point or the other, we as ASP.NET developers, have faced the requirement of reading and writing images to the database. We have seen loads of articles floating on the internet which discusses about storing and retrieving images from the database. Some of them are good. However, I have personally found that the solutions offered are those, where images are displayed in a ‘standalone fashion’; that is on a separate page containing only the image. What if we have to show an online form, with the person’s details and his photo along with it, or for that case, display the image in an ASP.NET server control along with other controls? In this article, we will explore how to store images in the database and then display those images along with the other server controls.
To keep the article simple and easy to understand, we will place only a few controls on the page. I have also not covered any validations associated with image control. In this article, we will only discuss how to read and write images into the database, and that would be the focus for this article. If you are interested in discussing validation and other stuff, I would suggest you to browse through the ASP.NET section of this website to view an article that discusses that.
So let us get started. We will first see how to upload an image and then display the uploaded image on the same page. You can extend this sample to create a photo album as well!! I assume you have some knowledge of creating ASP.NET 2.0 websites.
Let us start off by first creating a sample database and adding a table to it. We will call the database ‘Employee’ and the table will be called ‘EmpDetails’. This table will contain an image column along with some other columns. Run the following script in your SQL 2005 Query window (or server explorer) to construct the database and the table.
Database Script
CREATE DATABASE [Employee]
GO
USE [Employee]
GO
CREATE TABLE EmpDetails
(
empid int IDENTITY NOT NULL,
empname varchar(20),
empimg image
)
Step 1: Create a new asp.net website. In the code-behind, add the following namespace
C#
using System.Data.SqlClient;
VB.NET
Imports System.Data.SqlClient
Step 2: Drag and drop two label and one textbox control. Also drag drop a FileUpload control and a button control to upload the selected image on button click. As mentioned earlier, there are no validations performed. The source would look similar to the following:

Step 3: In the button click event, add the following code:
C#
protected void btnSubmit_Click(object sender, EventArgs e)
{
SqlConnection connection = null;
try
{
FileUpload img = (FileUpload)imgUpload;
Byte[] imgByte = null;
if (img.HasFile && img.PostedFile != null)
{
//To create a PostedFile
HttpPostedFile File = imgUpload.PostedFile;
//Create byte Array with file len
imgByte = new Byte[File.ContentLength];
//force the control to load data in array
File.InputStream.Read(imgByte, 0, File.ContentLength);
}
// Insert the employee name and image into db
string conn = ConfigurationManager.ConnectionStrings ["EmployeeConnString"].ConnectionString;
connection = new SqlConnection(conn);

connection.Open();
string sql = "INSERT INTO EmpDetails(empname,empimg) VALUES(@enm, @eimg) SELECT @@IDENTITY";
SqlCommand cmd = new SqlCommand(sql, connection);
cmd.Parameters.AddWithValue("@enm", txtEName.Text.Trim());
cmd.Parameters.AddWithValue("@eimg", imgByte);
int id = Convert.ToInt32(cmd.ExecuteScalar());
lblResult.Text = String.Format("Employee ID is {0}", id);
}
catch
{
lblResult.Text = "There was an error";
}
finally
{
connection.Close();
}

}
VB.NET
Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
Dim connection As SqlConnection = Nothing
Try
Dim img As FileUpload = CType(imgUpload, FileUpload)
Dim imgByte As Byte() = Nothing
If img.HasFile AndAlso Not img.PostedFile Is Nothing Then
'To create a PostedFile
Dim File As HttpPostedFile = imgUpload.PostedFile
'Create byte Array with file len
imgByte = New Byte(File.ContentLength - 1) {}
'force the control to load data in array
File.InputStream.Read(imgByte, 0, File.ContentLength)
End If
' Insert the employee name and image into db
Dim conn As String = ConfigurationManager.ConnectionStrings("EmployeeConnString").ConnectionString
connection = New SqlConnection(conn)

connection.Open()
Dim sql As String = "INSERT INTO EmpDetails(empname,empimg) VALUES(@enm, @eimg) SELECT @@IDENTITY"
Dim cmd As SqlCommand = New SqlCommand(sql, connection)
cmd.Parameters.AddWithValue("@enm", txtEName.Text.Trim())
cmd.Parameters.AddWithValue("@eimg", imgByte)
Dim id As Integer = Convert.ToInt32(cmd.ExecuteScalar())
lblResult.Text = String.Format("Employee ID is {0}", id)
Catch
lblResult.Text = "There was an error"
Finally
connection.Close()
End Try
End Sub
In the code above, we are creating a byte array equal to the length of the file. The byte array will store the image. We then load the image data into the array. The record containing the Employee Name and Image is then inserted into the database using the ADO.NET code. The ID inserted is returned back using the @@Identity. We will shortly use this ID and pass it as a query string parameter to the ShowImage handler. The image will then be fetched against the EmployeeID (empid).
Step 4: In order to display the image on the page, we will create an Http handler. To do so, right click project > Add New Item > Generic Handler > ShowImage.ashx. The code shown below, uses the Request.QueryString[“id”] to retrieve the EmployeeID from it. The ID is then passed to the ‘ShowEmpImage()’ method where the image is fetched from the database and returned in a MemoryStream object. We then read the stream into a byte array. Using the OutputStream.Write(), we write the sequence of bytes to the current stream and you get to see your image.
C#
<%@ WebHandler Language="C#" Class="ShowImage" %>

using System;
using System.Configuration;
using System.Web;
using System.IO;
using System.Data;
using System.Data.SqlClient;

public class ShowImage : IHttpHandler
{
public void ProcessRequest(HttpContext context)
{
Int32 empno;
if (context.Request.QueryString["id"] != null)
empno = Convert.ToInt32(context.Request.QueryString["id"]);
else
throw new ArgumentException("No parameter specified");

context.Response.ContentType = "image/jpeg";
Stream strm = ShowEmpImage(empno);
byte[] buffer = new byte[4096];
int byteSeq = strm.Read(buffer, 0, 4096);

while (byteSeq > 0)
{
context.Response.OutputStream.Write(buffer, 0, byteSeq);
byteSeq = strm.Read(buffer, 0, 4096);
}
//context.Response.BinaryWrite(buffer);
}

public Stream ShowEmpImage(int empno)
{
string conn = ConfigurationManager.ConnectionStrings ["EmployeeConnString"].ConnectionString;
SqlConnection connection = new SqlConnection(conn);
string sql = "SELECT empimg FROM EmpDetails WHERE empid = @ID";
SqlCommand cmd = new SqlCommand(sql,connection);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@ID", empno);
connection.Open();
object img = cmd.ExecuteScalar();
try
{
return new MemoryStream((byte[])img);
}
catch
{
return null;
}
finally
{
connection.Close();
}
}

public bool IsReusable
{
get
{
return false;
}
}


}
VB.NET
<%@ WebHandler Language="vb" Class="ShowImage" %>

Imports System
Imports System.Configuration
Imports System.Web
Imports System.IO
Imports System.Data
Imports System.Data.SqlClient

Public Class ShowImage
Implements IHttpHandler
Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
Dim empno As Int32
If Not context.Request.QueryString("id") Is Nothing Then
empno = Convert.ToInt32(context.Request.QueryString("id"))
Else
Throw New ArgumentException("No parameter specified")
End If

context.Response.ContentType = "image/jpeg"
Dim strm As Stream = ShowEmpImage(empno)
Dim buffer As Byte() = New Byte(4095) {}
Dim byteSeq As Integer = strm.Read(buffer, 0, 4096)

Do While byteSeq > 0
context.Response.OutputStream.Write(buffer, 0, byteSeq)
byteSeq = strm.Read(buffer, 0, 4096)
Loop
'context.Response.BinaryWrite(buffer);
End Sub

Public Function ShowEmpImage(ByVal empno As Integer) As Stream
Dim conn As String = ConfigurationManager.ConnectionStrings("EmployeeConnString").ConnectionString
Dim connection As SqlConnection = New SqlConnection(conn)
Dim sql As String = "SELECT empimg FROM EmpDetails WHERE empid = @ID"
Dim cmd As SqlCommand = New SqlCommand(sql, connection)
cmd.CommandType = CommandType.Text
cmd.Parameters.AddWithValue("@ID", empno)
connection.Open()
Dim img As Object = cmd.ExecuteScalar()
Try
Return New MemoryStream(CType(img, Byte()))
Catch
Return Nothing
Finally
connection.Close()
End Try
End Function

Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
Get
Return False
End Get
End Property


End Class
Step 5: One final step. Add the following code in the button click (just above the catch block) to call the handler and display the newly inserted image from the database. In the code below, we pass the EmployeeID as a query string parameter to the Http Handler.
C#
// Display the image from the database
Image1.ImageUrl = "~/ShowImage.ashx?id=" + id;
VB.NET
' Display the image from the database
Image1.ImageUrl = "~/ShowImage.ashx?id=" & id
That’s it. Run the code and check out the functionality. Just change the connection string in the web.config to point to your database. The code works fine for .jpg, .gif and .bmp images. I would encourage you to extend the sample and include validations in it. Some validations could be to check the size of the image uploaded, make sure that only images are uploaded, check the length of the Employee name, prevent the user from entering numeric and special characters, so on and so forth.

Dotnet Basic Questions

What is ASP.NET?
Microsoft ASP.NET is a server side technology that enables programmers to build dynamic Web sites, web applications, and XML Web services. It is a part of the .NET based environment and is built on the Common Language Runtime (CLR) . So programmers can write ASP.NET code using any .NET compatible language.
What are the differences between ASP.NET 1.1 and ASP.NET 2.0?
A comparison chart containing the differences between ASP.NET 1.1 and ASP.NET 2.0 can be found over here.
Which is the latest version of ASP.NET? What were the previous versions released?
The latest version of ASP.NET is 2.0. There have been 3 versions of ASP.NET released as of date. They are as follows :
ASP.NET 1.0 – Released on January 16, 2002.
ASP.NET 1.1 – Released on April 24, 2003.
ASP.NET 2.0 – Released on November 7, 2005.
Additionally, ASP.NET 3.5 is tentatively to be released by the end of the 2007.
Explain the Event Life cycle of ASP.NET 2.0?
The events occur in the following sequence. Its best to turn on tracing() and track the flow of events :
PreInit – This event represents the entry point of the page life cycle. If you need to change the Master page or theme programmatically, then this would be the event to do so. Dynamic controls are created in this event.
Init – Each control in the control collection is initialized.
Init Complete* - Page is initialized and the process is completed.
PreLoad* - This event is called before the loading of the page is completed.
Load – This event is raised for the Page and then all child controls. The controls properties and view state can be accessed at this stage. This event indicates that the controls have been fully loaded.
LoadComplete* - This event signals indicates that the page has been loaded in the memory. It also marks the beginning of the rendering stage.
PreRender – If you need to make any final updates to the contents of the controls or the page, then use this event. It first fires for the page and then for all the controls.
PreRenderComplete* - Is called to explicitly state that the PreRender phase is completed.
SaveStateComplete* - In this event, the current state of the control is completely saved to the ViewState.
Unload – This event is typically used for closing files and database connections. At times, it is also used for logging some wrap-up tasks.
The events marked with * have been introduced in ASP.NET 2.0.
You have created an ASP.NET Application. How will you run it?
With ASP.NET 2.0, Visual Studio comes with an inbuilt ASP.NET Development Server to test your pages. It functions as a local Web server. The only limitation is that remote machines cannot access pages running on this local server. The second option is to deploy a Web application to a computer running IIS version 5 or 6 or 7.
Explain the AutoPostBack feature in ASP.NET?
AutoPostBack allows a control to automatically postback when an event is fired. For eg: If we have a Button control and want the event to be posted to the server for processing, we can set AutoPostBack = True on the button.
How do you disable AutoPostBack?
Hence the AutoPostBack can be disabled on an ASP.NET page by disabling AutoPostBack on all the controls of a page. AutoPostBack is caused by a control on the page.
What are the different code models available in ASP.NET 2.0?
There are 2 code models available in ASP.NET 2.0. One is the single-file page and the other one is the code behind page.
Which base class does the web form inherit from?
Page class in the System.Web.UI namespace.
Which are the new special folders that are introduced in ASP.NET 2.0?
There are seven new folders introduced in ASP.NET 2.0 :
\App_Browsers folder – Holds browser definitions(.brower) files which identify the browser and their capabilities.
\App_Code folder – Contains source code (.cs, .vb) files which are automatically compiled when placed in this folder. Additionally placing web service files generates a proxy class(out of .wsdl) and a typed dataset (out of .xsd).
\App_Data folder – Contains data store files like .mdf (Sql Express files), .mdb, XML files etc. This folder also stores the local db to maintain membership and role information.
\App_GlobalResources folder – Contains assembly resource files (.resx) which when placed in this folder are compiled automatically. In earlier versions, we were required to manually use the resgen.exe tool to compile resource files. These files can be accessed globally in the application.
\App_LocalResources folder – Contains assembly resource files (.resx) which can be used by a specific page or control.
\App_Themes folder – This folder contains .css and .skin files that define the appearance of web pages and controls.
\App_WebReferences folder – Replaces the previously used Web References folder. This folder contains the .disco, .wsdl, .xsd files that get generated when accessing remote web services.
Explain the ViewState in ASP.NET?
Http is a stateless protocol. Hence the state of controls is not saved between postbacks. Viewstate is the means of storing the state of server side controls between postbacks. The information is stored in HTML hidden fields. In other words, it is a snapshot of the contents of a page.
You can disable viewstate by a control by setting the EnableViewState property to false.
What does the EnableViewState property signify?
EnableViewState saves the state of an object in a page between postbacks. Objects are saved in a Base64 encoded string. If you do not need to store the page, turn it off as it adds to the page size.
There is an excellent article by Peter Bromberg to understand Viewstate in depth.
Explain the ASP.NET Page Directives?
Page directives configure the runtime environment that will execute the page. The complete list of directives is as follows:
@ Assembly - Links an assembly to the current page or user control declaratively.
@ Control - Defines control-specific attributes used by the ASP.NET page parser and compiler and can be included only in .ascx files (user controls).
@ Implements - Indicates that a page or user control implements a specified .NET Framework interface declaratively.
@ Import - Imports a namespace into a page or user control explicitly.
@ Master - Identifies a page as a master page and defines attributes used by the ASP.NET page parser and compiler and can be included only in .master files.
@ MasterType - Defines the class or virtual path used to type the Master property of a page.
@ OutputCache - Controls the output caching policies of a page or user control declaratively.
@ Page - Defines page-specific attributes used by the ASP.NET page parser and compiler and can be included only in .aspx files.
@ PreviousPageType - Creates a strongly typed reference to the source page from the target of a cross-page posting.
@ Reference - Links a page, user control, or COM control to the current page or user control declaratively.
@ Register - Associates aliases with namespaces and classes, which allow user controls and custom server controls to be rendered when included in a requested page or user control.
This list has been taken from here.
Explain the Validation Controls used in ASP.NET 2.0?
Validation controls allows you to validate a control against a set of rules. There are 6 different validation controls used in ASP.NET 2.0.
RequiredFieldValidator – Checks if the control is not empty when the form is submitted.
CompareValidator – Compares the value of one control to another using a comparison operator (equal, less than, greater than etc).
RangeValidator – Checks whether a value falls within a given range of number, date or string.
RegularExpressionValidator – Confirms that the value of a control matches a pattern defined by a regular expression. Eg: Email validation.
CustomValidator – Calls your own custom validation logic to perform validations that cannot be handled by the built in validators.
ValidationSummary – Show a summary of errors raised by each control on the page on a specific spot or in a message box.
How do you indentify that the page is post back?
By checking the IsPostBack property. If IsPostBack is True, the page has been posted back.
What are Master Pages?
Master pages is a template that is used to create web pages with a consistent layout throughout your application. Master Pages contains content placeholders to hold page specific content. When a page is requested, the contents of a Master page are merged with the content page, thereby giving a consistent layout.
How is a Master Page different from an ASP.NET page?
The MasterPage has a @Master top directive and contains ContentPlaceHolder server controls. It is quiet similar to an ASP.NET page.
How do you attach an exisiting page to a Master page?
By using the MasterPageFile attribute in the @Page directive and removing some markup.
How do you set the title of an ASP.NET page that is attached to a Master Page?
By using the Title property of the @Page directive in the content page. Eg:
<@Page MasterPageFile="Sample.master" Title="I hold content" %>
What is a nested master page? How do you create them?
A Nested master page is a master page associated with another master page. To create a nested master page, set the MasterPageFile attribute of the @Master directive to the name of the .master file of the base master page.
What are Themes?
Themes are a collection of CSS files, .skin files, and images. They are text based style definitions and are very similar to CSS, in that they provide a common look and feel throughout the website.
What are skins?
A theme contains one or more skin files. A skin is simply a text file with a .skin extension and contains definition of styles applied to server controls in an ASP.NET page. For eg:

Defines a skin that will be applied to all buttons throughout to give it a consistent look and feel.
What is the difference between Skins and Css files?
Css is applied to HTML controls whereas skins are applied to server controls.
What is a User Control?
User controls are reusable controls, similar to web pages. They cannot be accessed directly.
Explain briefly the steps in creating a user control?
· Create a file with .ascx extension and place the @Control directive at top of the page.
· Included the user control in a Web Forms page using a @Register directive
What is a Custom Control?
Custom controls are compiled components that run on the server and that encapsulate user-interface and other related functionality into reusable packages. They can include all the design-time features of standard ASP.NET server controls, including full support for Visual Studio design features such as the Properties window, the visual designer, and the Toolbox.
What are the differences between user and custom controls?
User controls are easier to create in comparison to custom controls, however user controls can be less convenient to use in advanced scenarios.
User controls have limited support for consumers who use a visual design tool whereas custom controls have full visual design tool support for consumers.
A separate copy of the user control is required in each application that uses it whereas only a single copy of the custom control is required, in the global assembly cache, which makes maintenance easier.
A user control cannot be added to the Toolbox in Visual Studio whereas custom controls can be added to the Toolbox in Visual Studio.
User controls are good for static layout whereas custom controls are good for dynamic layout.
Where do you store your connection string information?
The connection string can be stored in configuration files (web.config).
What is the difference between ‘Web.config’ and ‘Machine.config’?
Web.config files are used to apply configuration settings to a particular web application whereas machine.config file is used to apply configuration settings for all the websites on a web server.
Web.config files are located in the application's root directory or inside a folder situated in a lower hierarchy. The machine.config is located in the Windows directory Microsoft.Net\Framework\Version\CONFIG.
There can be multiple web.config files in an application nested at different hierarchies. However there can be only one machine.config file on a web server.
What is the difference between Server.Transfer and Response.Redirect?
Response.Redirect involves a roundtrip to the server whereas Server.Transfer conserves server resources by avoiding the roundtrip. It just changes the focus of the webserver to a different page and transfers the page processing to a different page.
Response.Redirect can be used for both .aspx and html pages whereas Server.Transfer can be used only for .aspx pages.
Response.Redirect can be used to redirect a user to an external websites. Server.Transfer can be used only on sites running on the same server. You cannot use Server.Transfer to redirect the user to a page running on a different server.
Response.Redirect changes the url in the browser. So they can be bookmarked. Whereas Server.Transfer retains the original url in the browser. It just replaces the contents of the previous page with the new one.
What method do you use to explicitly kill a users session?
Session.Abandon().
What is a webservice?
Web Services are applications delivered as a service on the Web. Web services allow for programmatic access of business logic over the Web. Web services typically rely on XML-based protocols, messages, and interface descriptions for communication and access. Web services are designed to be used by other programs or applications rather than directly by end user. Programs invoking a Web service are called clients. SOAP over HTTP is the most commonly used protocol for invoking Web services.