Understanding Page Class in ASP.NET 2.0
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by SANJIT SIL
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Objects

Let us now discuss the various objects of the Page class.

Session

The session object is an instance of the System.Web.SessionState.HttpSessionState class. It acts as a global repository to store any type of user specific data that needs to persist between web-page requests. The session object stores data in the form of name/value pairs which is used to maintain data like user's name, user's ID, a shopping cart and other elements which are discarded when a user logs out or is not accessing any page of the web site. Session sate can be both in process and out process.

Application

The Application object is an instance of the System.Web.HttpApplicationState class. Like session object, it also stores data in the form of name/value pairs. However, the scope of this data is global to the entire application.

Cache

Cache object is an instance of the System.Web.Caching.Cache class. It also stores global information. It is also a name/value collection of objects, but we can set customized expiration policies and dependencies for each item so that items are automatically removed when other resources, such as files or database tables, are modified.

Request

The request object is an instance of the System.Web.HttpRequest class. It represents the values and properties of the HTTP request that caused our page to be loaded. It contains all the URL parameters and all other information sent by the client.

HttpRequest Properties

·         ApplicationPath and PhysicalPath

ApplicationPath gets the ASP.NET application's virtual application root path on server while PhysicalPath gets the Physical file system path corresponding to the requested URL.

·         AnonymousID

This uniquely identifies the current user if we have enabled anonymous access.

·         Browser

This provides a link to the requesting client's browser capabilities object.

·         ClientCertificate

This is an HttpClientCertificate object that gets the security certificate for the current request.

·         Cookies

This gets the collection cookies sent with this request

·         FilePath and CurrentExecutionFilePath

These return the virtual path of the current request.

·         Form

This represents the collection of form variables that were posted back to the page. In almost all cases we will retrieve the information from control properties instead of using this collection

·         ServerVariables: This Returns a collection of named server variables sent with the request.

·         IsAuthenticated: This returns true if the user has been successfully authenticated.

·         IsSecureConnection: This indicates whether the HTTP connection uses secure sockets (that is, HTTPS).

·         Islocal: This returns true if the user is requesting the page from the current system.

·         QueryString: This provides the parameters that are passed along with the query string.

·          UrlReferrer: This provides a Url object that represents the current address for the page where the user is coming from (the previous page that linked to this page).

·         UserAgent: This is a string representing the browser type.

·         UserHostAddress and UserHostName: These get the IP address and the DNS name of the remote client.

·         UserLanguages: This provides a stored string array of client’s language preference. This can be useful if we need to create multilingual pages.

Response

The Response object is an instance of the System.Web.HttpResponse class, and it represents the web server’s response to a client request.

HttpResponse Members:

·         Buffer Output

When set to true (the default), the page is not sent to the client until the entire page is finished processing.

·         Cache

It allows us to configure output caching of a Web page.

·         Cookies

This is the collection of cookies sent with the response.

·         Expires and Expires Absolute

We can use these properties to cache the rendered HTML for the page for a specified period of time, which helps to improve performance for subsequent requests.

·         IsClientConnected

 This is a Boolean value which indicates whether the client is still connected to the server.

·         Redirect()

This method transfers the user to another page in the application or to a different web site.

·         ContentType

The ContentType is a header that tells the browser what type of content it is about to receive. In general, ASP.NET web forms use text or html content type. However, we can create a custom HTTP handler that serves different types of content.

·         OutputStream

It represents the data we are sending to the browser as a stream of raw bytes.

·         Write()

This method allows us to write text directly to the response stream.

·         BinaryWrite() and WriteFile()

These methods allow us to take binary content from a byte array or form a file and write it directly to the response stream.

Server

The Server object is an instance of the System.Web.HttpServerUtility class. It provides different methods and properties.

·         MachineName

A property representing the computer name of the computer on which the page is running, that means the server.

·          CreateObject() 

Creates an instance of the COM object that is identified by the object's programmatic identifier (ProgID).

·          GetLastError 

This retrieves the exception object for the most recently encountered error. This is most commonly used in an application event handler that checks for error conditions.

Listing 1

Exception LastError;
String ErrMsg;
 
LastError = Server.GetLastError();
 
if (LastError != null)
   ErrMsg = LastError.Message;
else
   ErrMsg = "No Errors";
 
Response.Write("Last Error = " + ErrMsg);

·         HtmlEncode() and HtmlDecode():

Changes an ordinary string into a string with legal HTML characters (and back again).

Listing 2

String TestString = "This is a <Test String>.";
String EncodedString = Server.HtmlEncode(TestString);

·         UrlEncode() and UrlDecode():

Changes an ordinary string into a string with legal URL characters (and back again).

Listing 3

String MyURL;
MyURL = "http://www.technology.com/articles.aspx?title=" + 
  Server.UrlEncode("ASP.NET Code Snippets");
 
Response.Write("<a href=" + MyURL + "> ASP.NET Code Snippets </a>");
 
String DecodedString = Server.UrlDecode(EncodedString);

·         UrlEncodeToken() and  URLDecodeToken()

Performs the same work as UrlEncode() and UrlDecode(), except they work on a byte array that contains Base64 encoded data.

·         MapPath()

Returns the physical file path that corresponds to a specified virtual file path on the web server.

Listing 4

String FilePath;
FilePath = Server.MapPath("/MyPortalSite");

·         Transfer()

It can not be used to transfer the user to the site on another web server or to a non ASP.NET page (such as HTML page or an ASP page). Using Response.Redirect we can also move to another page. The Response.Redirect method sends a message to the requesting client to request a new page. This requires a round trip between the browser and the server, but allows the user to see the new URL in the browser address bar. Server.Transfer is a quicker approach in that ASP.NET simply loads the specified page without the round trip. As a result, the browser’s address bar is not changed.

User

The User object represents a person browsing and using the applications on a Web site and it allows us to test that user's role membership. We can authenticate a user based on Windows account information using IIS or through cookie based authentication with a dedicated login page. If our web application is performing some sort of authentication that restricts anonymous users then the user object provides useful information.

Trace

For tracing reader can read my article titled Understanding Tracing in ASP.NET


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