MCAD/MCSD: Implementing Navigation for the User Interface

This chapter is from the book

MCAD/MCSD Training Guide (70-315): Developing and Implementing Web Applications with Visual C# and Visual Studio.NET

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This chapter is from the book

This chapter is from the book 

MCAD/MCSD Training Guide (70-315): Developing and Implementing Web Applications with Visual C# and Visual Studio.NET

Learn More Buy

ASP.NET Intrinsic Objects

Use and edit intrinsic objects. Intrinsic objects include response, request, session, server, and application.

• Retrieve values from the properties of intrinsic objects.

• Set values on the properties of intrinsic objects.

• Use intrinsic objects to perform operations.

ASP.NET provides intrinsic objects to enable low-level access to the Web application framework. With the help of these intrinsic objects, you can work directly with the underlying HTTP streams, server, session, and application objects. The intrinsic objects can be accessed in a Web form through the properties of the Page class. Table 3.1 lists the important intrinsic objects and the properties of the Page class to which they are mapped.

Table 3.1 Intrinsic Objects and Their Mappings to the Page Class Properties

I'll discuss the HttpRequest, HttpResponse, and HttpServerUtility objects in the following section. The other two objects, HttpApplicationState and HttpSessionState, are discussed later in this chapter in the section "State Management."

The HttpRequest Object

The HttpRequest object . represents the incoming request from the client to the Web server. The request from the client can come in two ways—GET or POST. GET attaches the data with the URL, whereas POST embeds the data within the HTTP request body.

The requested page and its details are encapsulated in an HttpRequest object. The HttpRequest intrinsic object can be accessed by the Request property of the Page class. Tables 3.2 and 3.3 list the properties and methods of the HttpRequest class, respectively. Because the HttpRequest class provides information about the request sent by the client, all the properties are read-only except the Filter property.

Table 3.2 Properties of the HttpRequest Class

Table 3.3 Methods of the HttpRequest Class

Step by Step 3.3 displays some of the path-related properties of the HttpRequest object and calls the MapPath() method to get the physical file system path for a specified virtual path. It also displays the header information sent by the client to the server when the StepByStep3_3.aspx page is requested from the server.

STEP BY STEP

3.3 Using the HttpRequest Intrinsic Object

1. Add a new Web form to the project. Name the Web form StepByStep3_3.aspx. Change the pageLayout property of the DOCUMENT element to FlowLayout.

2. Add a Label control (lblInfo) to the Web form.

3. Switch to the code view of the form. Add the following using directive at the top of the code-behind file:

using System.Text;

4. Add the following code to the Page_Load() event handler:

private void Page_Load(
  object sender, System.EventArgs e)
{
  StringBuilder sbInfo = new StringBuilder();

  // Display some of the path related properties 
  // of the HttpRequest object
  sbInfo.Append("The Url of the ASPX page: " + 
    Request.Url + "<br>");
  sbInfo.Append("The Virtual File Path: " + 
    Request.FilePath + "<br>");
  sbInfo.Append("The Physical File Path: " + 
    Request.PhysicalPath + "<br>");
  sbInfo.Append("The Application Path: " + 
    Request.ApplicationPath + "<br>");
  sbInfo.Append("The Physical Application Path: " +
    Request.PhysicalApplicationPath + "<br>");

  // Display the request header
  sbInfo.Append("Request Header:");
  sbInfo.Append("<br>");
  NameValueCollection nvcHeaders = Request.Headers;
  String[] astrKeys = nvcHeaders.AllKeys;
  // Iterate through all header keys 
  // and display their values
  foreach (String strKey in astrKeys)
  {
    sbInfo.Append(strKey + ": " + 
      nvcHeaders[strKey].ToString());
    sbInfo.Append("<br>");
  }
  // Call MapPath() method to find the physical path
  // of StepByStep3_2.aspx
  sbInfo.Append(
    "The physical path of StepByStep3_2.aspx: ");
  sbInfo.Append(
    Request.MapPath("StepByStep3_2.aspx"));
  lblInfo.Text = sbInfo.ToString();
}

5. Set StepByStep3_3.aspx as the start page in the project.

6. Run the project. You should see the Web form displaying the properties for the current request, as shown in Figure 3.3.

Figure 3.3 The Request property of the Page class returns an HttpRequest object that gives access to the HTTP values sent by a client during a Web request.

Some properties of the HttpRequest object—such as Form, QueryString, Headers, and so on—return a NameValueCollection containing a collection of key-value pairs of their contents. Step by Step 3.3 shows how to iterate through this collection by iterating through the keys of the Headers collection and displaying the key and value of each header sent by the client.

The HttpResponse Object

The HttpResponse object represents the response sent back to the client from the Web server. It contains properties and methods that provide direct access to the response stream and allow you to set its behavior and operations. The Response property of the Page class provides access to the HttpResponse object. Tables 3.4 and 3.5 list the properties and methods of the HttpResponse class, respectively.

Table 3.4 Properties of the HttpResponse Class

Table 3.5 Methods of the HttpResponse Class

Step by Step 3.4 shows the use of HttpResponse object methods and properties to create a response that displays the File Download dialog box and allows the user to download a text file from the Web server to the client's machine.

STEP BY STEP

3.4 Using the HttpResponse Intrinsic Object

1. Add a new Web form to the project. Name the Web form StepByStep3_4.aspx. Change the pageLayout property of the DOCUMENT element to FlowLayout.

2. Add a text file to the project that contains some data that needs to be downloaded. Name it Summary.txt.

3. Add a LinkButton control (lbtnDownload) to the Web form with its Text property set to Download Summary.txt.

4. Double-click the lbtnDownload control and add the following code to the Click event handler:

private void lbtnDownload_Click(object sender, 
  System.EventArgs e)
{
  // Append a Header to the response to force a
  // Download of Summary.txt as an attachment
  Response.AppendHeader("Content-Disposition", 
    "Attachment;FileName=" + "Summary.txt");

  // Set the Content type to text/plain 
  // As the download file is a TXT file
  Response.ContentType = "text/plain";

  // Write the file to the Response
  Response.WriteFile("Summary.txt");

  // Stop further execution of the page
  Response.End();
}

5. Set StepByStep3_4.aspx as the start page in the project.

6. Run the project. Click the link button. You should see a File Download dialog box, as shown in Figure 3.4. After the download, open the file to verify that the file has been successfully downloaded.

Figure 3.4 The File Download dialog box provides the interface to download a file from the Web server.

The HttpServerUtility Object

The HttpServerUtility object contains utility methods and properties to work with the Web server. It contains methods to enable HTML/URL encoding and decoding, execute or transfer to an ASPX page, create COM components, and so on. The Server property of the Page class provides access to the HttpServerUtility object. Tables 3.6 and 3.7 list the properties and methods of the HttpServerUtility class, respectively.

Table 3.6 Properties of the HttpServerUtility Class

Table 3.7 Methods of the HttpServerUtility Class

STEP BY STEP

3.5 Using the HttpServerUtility Intrinsic Object

1. Add a new Web form to the project. Name the Web form StepByStep3_5.aspx. Change the pageLayout property of DOCUMENT element to FlowLayout.

2. Add the following code to the Page_Load() event handler:

private void Page_Load(
  object sender, System.EventArgs e)
{
  // Write to the response
  // using the Server.HtmlEncode() method
  // so that the browser does not parse
  // the text into HTML elements
  Response.Write(Server.HtmlEncode(
    "To include a title in the title bar, " + 
    "enclose your chosen title between the " + 
    "pairs of the <title>...</title> element " + 
    "in the HTML <head> element. "));

  Response.Write(Server.HtmlEncode(
    "For example, <title> " + 
    "Using the HtmlEncode() method </title>."));
}

3. Set StepByStep3_5.aspx as the Start page in the project.

4. Run the project. You should see that the browser does not parse the HTML <title> elements written to the response, as shown in Figure 3.5, because of the use of the HtmlEncode() method of the HttpServerUtility class.

Figure 3.5 The HtmlEncode() method of the HttpServerUtility object. HTML encodes a string to be displayed in the browser.

I will discuss various other methods of the HttpServerUtility object throughout the course of this book.

Guided Practice Exercise 3.1

Several Web sites collect statistics about the browsers, operating system, and other settings on their users' computers. This data helps the Web sites customize their contents to target a large number of users. A common requirement for Web applications is to find out the browser versions of their users and then serve them files that are optimized for that particular browser version.

In this exercise, you are required to create a Web form that displays the following information about the client browser: the browser name, version, platform of the client's computer, the CLR version installed, JavaScript support, ECMA version, MS DOM version, and the W3C XML DOM version supported by the browser.

You can use the Request.Browser property to get access to the HttpBrowserCapabilities object that provides various properties that contain information on the capabilities of the client's browser.

How would you create a Web form that allows the Web page to get information about the browser?

You should try working through this problem on your own first. If you are stuck, or if you'd like to see one possible solution, follow these steps:

1. Open the project 315C03. Add a new Web form GuidedPracticeExercise3_1.aspx to the project. Change the pageLayout property of DOCUMENT element to FlowLayout.

2. Add a Label control (lblInfo) to the Web form.

3. Switch to the code view of the form. Add the following using directive at the top of the code-behind file:

using System.Text;

4. Add the following code to the Page_Load() event handler:

private void Page_Load(
  object sender, System.EventArgs e)
{
  StringBuilder sbText = new StringBuilder();

  // Get the reference to the 
  // HttpBrowserCapabilities object 
  HttpBrowserCapabilities browser = Request.Browser;

  // Display the properties of the 
  // HttpBrowserCapabilities Class
  sbText.AppendFormat("Browser : " + 
    browser.Browser + "<br>");
  sbText.AppendFormat("Browser Version: " + 
    browser.Version + "<br>");
  sbText.AppendFormat("Client's Platform: " + 
    browser.Platform + "<br>");
  sbText.AppendFormat(".NET CLR Version: " + 
    browser.ClrVersion + "<br>");
  sbText.AppendFormat("ECMA Script Version: " + 
    browser.EcmaScriptVersion + "<br>");
  sbText.AppendFormat("JavaScript Support: " + 
    browser.JavaScript + "<br>");
  sbText.AppendFormat(
   "Microsoft HTML Document Object Model Version: "
    + browser.MSDomVersion + "<br>");
  sbText.AppendFormat(
    "World Wide Web (W3C) XML Document " + 
    " Object Model Version: " + 
    browser.W3CDomVersion + "<br>");

  lblInfo.Text=sbText.ToString();
}

5. Set GuidedPracticeExercise3_1.aspx as the start page in the project.

6. Run the project. You should see the Web form displaying the properties of the browser as shown in Figure 3.6.

Figure 3.6 The HttpBrowserCapabilities object provides access to the capabilities of the client's browser.

If you have difficulty following this exercise, review the section "The HttpRequest Object" earlier in this chapter and perform Step by Step 3.3. Also, look at the .NET Framework documentation for the System.Web.HttpBrowserCapabilities class. After doing this review, try this exercise again.

REVIEW BREAK

• Web applications are disconnected in nature. Values of page variables and controls are not preserved across the page requests.

• You can use the Page.IsPostBack property to determine whether a page is being loaded for the first time or in response to a postback operation.

• ASP.NET has a feature called smart navigation that can greatly enhance the user experience of a Web page for the users of Internet Explorer 5.0 or higher browsers.

• ASP.NET provides intrinsic objects to enable low-level access to the Web application framework. With the help of these intrinsic objects, you can work directly with the underlying HTTP request, HTTP response, server, session, and application objects.