ASP.NET is more than the next version of Active Server Pages
(ASP); it provides a unified Web development model that includes the services
necessary for developers to build enterprise-class Web applications. While
ASP.NET is largely syntax compatible with ASP, it also provides a new
programming model and infrastructure for more scalable and stable applications
that help provide greater protection. You can feel free to augment your
existing ASP applications by incrementally adding ASP.NET functionality to them.
Advantages:
- Separation of Code from HTML
To make a clean sweep, with ASP.NET you have the ability to completely separate layout and business logic. This makes it much easier for teams of programmers and designers to collaborate efficiently. This makes it much easier for teams of programmers and designers to collaborate efficiently. - Support for compiled languages
developer can use VB.NET and access features such as strong typing and object-oriented programming. Using compiled languages also means that ASP.NET pages do not suffer the performance penalties associated with interpreted code. ASP.NET pages are precompiled to byte-code and Just In Time (JIT) compiled when first requested. Subsequent requests are directed to the fully compiled code, which is cached until the source changes. - Use services provided by the .NET Framework
The .NET Framework provides class libraries that can be used by your application. Some of the key classes help you with input/output, access to operating system services, data access, or even debugging. We will go into more detail on some of them in this module. - Graphical Development Environment
Visual Studio .NET provides a very rich development environment for Web
developers. You can drag and drop controls and set properties the way you do in Visual Basic 6. And you have full IntelliSense support, not only for your code, but also for HTML and XML. - State management
To refer to the problems mentioned before, ASP.NET provides solutions for session and application state management. State information can, for example, be kept in memory or stored in a database. It can be shared across Web farms, and state information can be recovered, even if the server fails or the connection breaks down. - Update files while the server is running!
Components of your application can be updated while the server is online and clients are connected. The Framework will use the new files as soon as they are copied to the application. Removed or old files that are still in use are kept in memory until the clients have finished. - XML-Based Configuration Files
Configuration settings in ASP.NET are stored in XML files that you can easily read and edit. You can also easily copy these to another server, along with the other files that comprise your application.
ASP.Net Application Life Cycle:
The application life cycle has the following stages:
User makes a request for accessing application
resource, a page. Browser sends this request to the web server.
A unified pipeline receives the first request and
the following events take place:
o
An object of the ApplicationManager class is
created.
o
An object of the HostingEnvironment class is
created to provide information regarding the resources.
o
Top level items in the application are compiled.
Response objects are created . the application objects:
HttpContext, HttpRequest and HttpResponse are created and initialized.
An instance of the HttpApplication object is
created and assigned to the request. The request is processed by the
HttpApplication class. Different events are raised by this class for processing
the request.
Architecture :
ASP.NET uses ISAPI to
run on the Internet Information Server (IIS) in Windows 2000 Server. Not
only does IIS host ASP.NET but the ISAPI filter mechanism also allows both ASP
and ASP.NET to coexist on the same IIS server. (IIS can direct a *.asp page to
ASP and a *.aspx page to ASP.NET.)The configuration of ASP.NET is managed by information stored in XML-format in a configuration file (Web.Config).
The cache allows for improved performance of ASP.NET, as the most commonly requested pages would be served from the ASP.NET cache.
State management services for ASP.NET are provided by the ASP.NET state service.
The .NET Framework provides the Common Language Runtime (CLR), which compiles and manages the execution of ASP.NET code, and the class libraries, which offer prebuilt programmatic functionality for Web Forms, XML support, and exception handling.
ADO.NET provides ASP.NET with connections to databases.
4)Page Structure:
Here is quick introduction
of syntax used in ASP.NET
Directives
You can use directives to specify
optional settings used by the page compiler when processing ASP.NET files. For
each directive you can set different attributes. One example is the language
directive at the beginning of a page defining the default programming language.
Code
Declaration Blocks
Code declaration blocks are lines of
code enclosed in <script> tags. They contain the runat=server attribute,
which tells ASP.NET that these controls can be accessed on the server and on
the client. Optionally you can specify the language for the block. The code
block itself consists of the definition of member variables and methods.
Code
Render Blocks
Render blocks contain inline code or
inline expressions enclosed by the character sequences shown here. The language
used inside those blocks could be specified through a directive like the one
shown before.
HTML
Control Syntax
You can declare several standard
HTML elements as HTML server controls. Use the element as you are familiar with
in HTML and add the attribute runat=server. This causes the HTML element to be
treated as a server control. It is now programmatically accessible by using a
unique ID. HTML server controls must reside within a <form> section that
also has the attribute runat=server.
Custom
Control Syntax
There are two different kinds of
custom controls. On the one hand there are the controls that ship with .NET,
and on the other hand you can create your own custom controls. Using custom
server controls is the best way to encapsulate common programmatic functionality.
Just specify elements as you did
with HTML elements, but add a tag prefix, which is an alias for the fully
qualified namespace of the control. Again you must include the runat=server
attribute. If you want to get programmatic access to the control, just add an
Id attribute.
You can include properties for each
server control to characterize its behavior. For example, you can set the
maximum length of a TextBox. Those properties might have sub properties; you
know this principle from HTML. Now you have the ability to specify, for
example, the size and type of the font you use (font-size and font-type).
The last attribute is dedicated to
event binding. This can be used to bind the control to a specific event. If you
implement your own method MyClick, this method will be executed when the corresponding button
is clicked if you use the server control event binding shown in the slide.
Data
Binding Expression
You can create bindings between
server controls and data sources. The data binding expression is enclosed by
the character sequences <%# and %>. The data-binding model provided by
ASP.NET is hierarchical. That means you can create bindings between server
control properties and superior data sources.
Server-side
Object Tags
If you need to create an instance of
an object on the server, use server-side object tags. When the page is
compiled, an instance of the specified object is created. To specify the object
use the identifier attribute. You can declare (and instantiate) .NET objects
using class as the identifier, and COM objects using either progid or classid.
Server-side
Include Directives
With server-side include directives
you can include raw contents of a file anywhere in your ASP.NET file. Specify
the type of the path to filename with the pathtype attribute. Use either File,
when specifying a relative path, or Virtual, when using a full virtual path.
Server-side
Comments
To prevent server code from
executing, use these character sequences to comment it out. You can comment out
full blocks - not just single lines.
ASP.NET Applications and Configuration:
The behavior of an ASP.Net application is affected by different settings in the configuration files:
·
machine.config
·
web.config
The machine.config file contains default and the machine-specific value for
all supported settings. The machine settings are controlled by the system
administrator and applications are generally not given access to this file.An application however, can override the default values by creating web.config files in its roots folder. The web.config file is a subset of the machine.config file.
If the application contains child directories, it can define a web.config file for each folder. Scope of each configuration file is determined in a hierarchical top-down manner.
Any web.config file can locally extend, restrict or override any settings defined on the upper level.
Visual Studio generates a default web.config file for each project. An application can run without a web.config file, however, you cannot debug an application without a web.config file.
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