Procedure 3.1. 3.1 Using the IsPostBack Property

1. Create a new Visual C# ASP.NET Web application project. Name the project 315C03.

2. Add a new Web form to the project. Name the Web form StepByStep3_1.aspx. Change the pageLayout property of the DOCUMENT element to FlowLayout.

3. Add a DropDownList Web server control (ddlCategories) to the form. Set its AutoPostBack to true and TabIndex to 1 (see Figure 3.1).

   

   Figure 3.1. The design of a form that allows you to post messages to a Weblog.

4. Add a Label control (lblQuestion) to the Web form.

5. Add a TextBox control (txtTitle) and set its AutoPostBack to true and TabIndex to 2. Add another TextBox (txtMessage) and set its TabIndex to 3 and TextMode to MultiLine (see Figure 3.1).

6. Add a Button control (btnPost) and set its Text to Post a message. Place a Label control (lblWeblog) at the end of the form as shown in Figure 3.1.

7. Switch to the code view of the Web form and add the following code to the Page_Load() event handler:

   private void Page_Load(
       object sender, System.EventArgs e)
   {
       if (!Page.IsPostBack)
       {
           // If page is requested for the first time
           ddlCategories.Items.Add("Web development");
           ddlCategories.Items.Add(
               "Programming Languages");
           ddlCategories.Items.Add("Certifications");
       }
       else
       {
           // On postback, change the case of
           // the textbox's text
           txtTitle.Text = txtTitle.Text.ToUpper();
       }
       // Set the text of the label control
       // on each page load
       lblQuestion.Text =
         "What do you want to write about "
         + ddlCategories.SelectedItem.Text + " today?";
   }
   

8. Attach the following event handler to the Click event of the Post button:

   private void btnPost_Click(
        object sender, System.EventArgs e)
   {
       // Format the data entered by the user and
       // append it to the existing contents of lblWeblog
       lblWeblog.Text = "<b>" +
                 ddlCategories.SelectedItem.Text
                + " :: " + txtTitle.Text + "</b> ("
                + DateTime.Now.ToString() + ")<hr>"
                + txtMessage.Text + "<p>"
                + lblWeblog.Text + "</p>";
   }
   

9. Set StepByStep3_1.aspx as the start page in the project.

10. Run the project. Use the Tab key to navigate between various fields and publish a few entries to the Weblog as shown in Figure 3.2.

    

    Figure 3.2. The Web form retains state for both postback as well as non-postback controls.

Procedure 3.2. 3.2 Using the Smart Navigation Feature of ASP.NET

1. Make a copy of StepByStep3_1 and save it as StepByStep3_2. Make sure that you change all references of StepByStep3_1 to StepByStep3_2 in both the ASPX as well as the CS file.

2. Switch to the HTML view of the StepByStep3_2.aspx file and modify the Page directive to the following:

   <%@ Page language="c#"
            Codebehind="StepByStep3_2.aspx.cs"
            AutoEventWireup="false"
            Inherits="_315C03.StepByStep3_2"
            SmartNavigation="true"
   %>
   

3. Set StepByStep3_2.aspx as the start page. Build the project and Browse to StepByStep3_2.aspx using Internet Explorer 5.0 or higher.

4. Use the Tab key to navigate between various fields, publish a few messages, and observe the enhancements because of the smart navigation feature.

Procedure 3.3. 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;
   using System.Collections.Specialized;

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.

Procedure 3.4. 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.

Procedure 3.5. 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.

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.

Procedure 3.13. 3.13 Using the Response.Redirect(), Server.Transfer(), and Server.Execute() Methods

1. Add a new Web form to the project. Name the Web form StepByStep3_13.aspx. Change the pageLayout property of the DOCUMENT element to FlowLayout.

2. Add three Label controls, a Literal control (litDynamic), two TextBox controls (txtRows, txtCells), and three Button controls (btnTransfer, btnExecute, and btnRedirect) to the Web form, as shown in Figure 3.12.

   

   Figure 3.12. The design of a form that allows you to specify rows and columns to create a table dynamically.

3. Add the following using directive to the form’s code: using System.IO;

4. Double-click the three Button controls to add an event handler to the Click event of each button. Add the following code in their event handlers:

   private void btnRedirect_Click(object sender,
       System.EventArgs e)
   {
       // Calling Response.Redirect by passing
       // Rows and Cells values as query strings
       Response.Redirect("StepByStep3_13a.aspx?Rows="
           + txtRows.Text + "&Cells=" + txtCells.Text);
   }
   
   private void btnTransfer_Click(object sender,
       System.EventArgs e)
   {
       // Writing into Response stream
       Response.Write(
           "The following table is generated " +
           "by StepByStep3_13a.aspx page:");
       // Calling the Server.Transfer method
       // with the second argument set to true
       // to preserve the form and query string data
       Server.Transfer("StepByStep3_13a.aspx", true);
       // Control does not come back here
   }
   
   private void btnExecute_Click(object sender,
       System.EventArgs e)
   {
       // Creating a StringWriter object
       StringWriter sw = new StringWriter();
       // Calling the Server.Execute method by
       // passing a StringWriter object
       Server.Execute("StepByStep3_13a.aspx", sw);
       // Control comes back
       // Displaying the output in the StringWriter
       // object in a Literal control
       litDynamic.Text = sw.ToString();
   }
   

5. Add a new Web form to the project. Name the Web form StepByStep3_13a.aspx. Change the pageLayout property of the DOCUMENT element to FlowLayout.

6. Add a Table control (tblDynamic) from the Web Forms tab of the Toolbox to the Web form.

7. Switch to the HTML view of the StepByStep3_13a.aspx file and modify the Page directive to add the EnableViewStateMac="false" attribute:

   <%@ Page language="c#"
        Codebehind="StepByStep3_13a.aspx.cs"
        AutoEventWireup="false"
        Inherits="_315C03.StepByStep3_13a"
        EnableViewStateMac="false"
   %>
   

8. Switch to code view and add the following method in the class definition:

   private void CreateTable(Int32 intRows, Int32 intCells)
   {
       // Create a new table
       TableRow trRow;
       TableCell tcCell;
   
       // Iterate for the specified number of rows
       for (int intRow=1; intRow <= intRows; intRow ++)
       {
           // Create a row
           trRow = new TableRow();
           if(intRow % 2 == 0)
           {
               trRow.BackColor = Color.LightBlue;
           }
           // Iterate for the specified number of columns
           for (int intCell=1; intCell <= intCells;
                intCell++)
           {
               // Create a cell in the current row
               tcCell = new TableCell();
               tcCell.Text = "Cell (" + intRow  + ","
                   + intCell + ")";
               trRow.Cells.Add(tcCell);
           }
           // Add the row to the table
           tblDynamic.Rows.Add(trRow);
       }
   }
   

9. Add the following code in the Page_Load() event handler:

   private void Page_Load(
       object sender, System.EventArgs e)
   {
       if(Request.Form["txtRows"] != null)
       {
           // If the request contains form data then the
           // page is called from the Server.Transfer or
           // Server.Execute methods from the
           // StepByStep3_13.aspx page. Get the Rows and
           // Cells values from the form collection and
           // Create a table.
           CreateTable(
               Int32.Parse(Request.Form["txtRows"]),
               Int32.Parse(Request.Form["txtCells"]));
       }
       else if(Request.QueryString["Rows"] != null)
       {
           // If the request contains query string data
           // that means the response is redirected from
           // the StepByStep3_14.aspx page. Get the Rows
           // and Cells value from the query string and
           // Create a table.
           Response.Write("StepByStep3_13a.aspx:");
           CreateTable(
               Int32.Parse(Request.QueryString["Rows"]),
               Int32.Parse(Request.QueryString["Cells"]));
       }
   }
   

10. Set StepByStep3_13.aspx as the start page in the project.

11. Run the project. Enter the number of rows and cells and click all three buttons one by one. When you click the Redirect button, the browser is redirected to StepByStep3_13a.aspx by passing the Rows and Cells values as the query string data as shown in Figure 3.13. When you click the Transfer button, the browser doesn't change the page name in the location bar, but the control gets transferred to the StepByStep3_13a.aspx page as shown in Figure 3.14. Finally, when you click the Execute button, the StepByStep3_13a.aspx page is executed and control comes back to the calling page, where the output of the Server.Execute() method is displayed as shown in Figure 3.15.

    

    Figure 3.13. The Response.Redirect() method can be used to navigate to a URL that contains query strings.

    

    Figure 3.14. The Server.Transfer() method is used to navigate to an ASPX page on the same server without causing an additional roundtrip.

    

    Figure 3.15. The Server.Execute() method executes the specified ASPX page and returns the control back to the calling page.

1. Expose the control values as public properties in the page that transfers the control.

2. In the target page, create an instance of the previous page's class.

3. Use the HttpContext.Handler property to retrieve the instance of the handler for the previous page. Initialize the object created in the preceding step with this value.

4. Use the instance of the previous page's class to access its properties.

1. Open the project 315C03. Add a new Web form GuidedPracticeExercise3_2 to the project. Change the pageLayout property of the DOCUMENT element to FlowLayout.

2. Add three Label controls, two TextBox controls (txtRows, txtCells), and one button control (btnTransfer) on the Web form.

3. Switch to the code view and add the following property definition in the class definition:

   // Declaring properties to expose
   // the number of Rows and Cells entered
   public Int32 Rows
   {
       get
       {
           return Int32.Parse(txtRows.Text);
       }
   }
   public Int32 Cells
   {
       get
       {
           return Int32.Parse(txtCells.Text);
       }
   }
   

4. Double-click the Transfer button control and add the following code in the Click event handler:

   private void btnTransfer_Click(object sender,
       System.EventArgs e)
   {
       // Writing into Response
       Response.Write(
           "The following table is generated " +
           "by GuidedPracticeExercise3_2a.aspx page:");
       // Calling the Server.Transfer method
       Server.Transfer("GuidedPracticeExercise3_2a.aspx");
       // Control does not come back here
   }
   

5. Add a new Web form to the project. Name the Web form GuidedPracticeExercise3_2a.aspx. Change the pageLayout property of the DOCUMENT element to FlowLayout.

6. Add a Table control (tblDynamic) from the Web Forms tab of the Toolbox to the Web form.

7. Switch to code view and add the following code in the class definition to create an instance of the GuidedPracticeExercise3_2 page:

   // Declare a variable to store an instance of
   // the GuidedPracticeExercise3_2 Web form
   public GuidedPracticeExercise3_2 pageExercise3_2;
   

8. Add the following code in the Page_Load() event handler:

   private void Page_Load(
       object sender, System.EventArgs e)
   {
       if(!IsPostBack)
       {
           // Because its the same request context,
           // get the reference to the
           // GuidedPracticeExercise3_2 page
           // through the current request Context.
           // Get the Rows and Cells value from  the
           // GuidedPracticeExercise3_2 Web form's
           // properties and Create a table.
           pageExercise3_2 = (GuidedPracticeExercise3_2)
               Context.Handler;
           CreateTable(pageExercise3_2.Rows,
               pageExercise3_2.Cells);
       }
   }
   

9. Switch to code view and add the following method in the class definition:

   private void CreateTable(Int32 intRows, Int32 intCells)
   {
       // Create a new table
       TableRow trRow;
       TableCell tcCell;
   
       // Iterate for the specified number of rows
       for (int intRow=1; intRow <= intRows; intRow ++)
       {
           // Create a row
           trRow = new TableRow();
           if(intRow % 2 == 0)
           {
               trRow.BackColor = Color.LightBlue;
           }
           // Iterate for the specified number of columns
           for (int intCell=1; intCell <= intCells;
               intCell++)
           {
               // Create a cell in the current row
               tcCell = new TableCell();
               tcCell.Text = "Cell (" + intRow  + ","
                   + intCell + ")";
               trRow.Cells.Add(tcCell);
           }
           // Add the row to the table
           tblDynamic.Rows.Add(trRow);
       }
   }
   

10. Set GuidedPracticeExercise3_2.aspx as the start page in the project.

11. Run the project. Enter the number of rows and cells and click the Transfer button. You should see that the browser doesn't changes the page name in the location bar, but the control gets transferred to the GuidedPracticeExercise3_2a.aspx page. The GuidedPracticeExercise3_2a.aspx page is able to access the Rows and Cells properties of the GuidedPracticeExercise3_2.aspx page via the HttpContext.Handler property.