434 Project 4 CREATING AN AIRLINE RESERVATION PORTAL
Exploring ASP.NET Web Applications
ASP.NET applications include Web pages that are used to interact with a user. These pages are referred to as Web forms. When you browse an ASP.NET Web site, you use its Web forms to retrieve and update information. You can retrieve and update information on an ASP.NET Web site by using Web form server controls.These controls help design the interface of your application and process user data at the ser ver.
In this section, I will explain the concept of Web forms and describe the controls that are provided by ASP.NET.
Introducing Web Forms
Web forms are ASP.NET components that enable you to create interactive and dynamic Web pages. Web forms also provide you with a rich set of controls that can programmed in any .NET-compatible language, such as Visual Basic .NET and Visual C#.
A Web form comprises two components, programming logic and form interface. By separating the two, ASP.NET makes it easy for you to concentrate on the programming logic of the application without worrying about how the text will be rendered on the Web form. The two components of a Web form are explained as follows:
Visual component. The visual component of a Web form is the .aspx file that contains the code for rendering a Web form.
Programming logic. The programming logic of a Web form is the logic used to generate the output for a Web form. The default option provided by Visual Studio .NET is to create this file as a code-behind file. When you create a code-behind file, the extension of the file is .aspx.cs or
.aspx.vb, depending upon whether you are coding your application in Visual C# or Visual Basic .NET. However, you can also create this code in a code-inline model in which the code is written in the .aspx file. This method was used in ASP 3.0.
To create high performance Web forms, you should understand how Web forms are processed. There are two processing methods, client-side and server-side. I will discuss these methods in detail in this section.
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Server-Side Processing
In the server-side processing method, the request from the client is passed to the server for validation. For example, when a user needs to add details about a new flight, the user specifies the required information on a Web form and submits the information to the server for processing. This is an example of server-side processing. In the SkyShark Airlines application, most of the processing needs to be performed at the server side. Therefore, you will see that this method is used most often in the Web forms created in the subsequent chapters of this project.
Each time a Web form is posted to the server for processing, data is processed and the same form or another form is displayed to the user. For example, when you specify flight details and query the database for status of a flight, the information is retrieved and the Web form is reconstructed to display the status of the flight.
Before a Web form is displayed, the Page_Load event for the Web form is generated. All server controls are loaded for the Web form in the Page_Load event. Similarly, when the user navigates away or closes a Web form, the Page_Unload event is generated. In the Page_Unload event, the page is removed from the memory and any clean-up code that might be required to free resources is executed.
This procedure has inherent performance overheads. Consider the case where you specify a ticket number and submit the form to retrieve ticket details. All controls will be reinstantiated each time the page is loaded. However, you need to change the values in one or more controls. There should be a way to retain the control state between round trips on the server. ASP.NET offers a solution to this problem.By setting the IsPostBack property of controls to true, you can retain the state of a control between round trips. In addition, the initialization code executes only after the IsPostBack property is set to true, which helps in averting performance overheads.
TIP
Round trips are generated when a user requests for the Web form that is displayed.
Client-Side Processing
The client-side processing method is used to perform client-side validation. For example, if a client needs to print a report, it needs to process the document at the
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client end and not at the server end. If you use client-side validation code, the load on your server can be considerably reduced. The performance of your application improves. In the SkyShark Airlines application, I will use client-side processing to print the reservation ticket that is generated for a passenger.
Web Form Server Controls
Web form server controls are used for designing the user interface of the application and posting data to the server. Although similar to HTML controls in appearance and operation, server controls run on the server. It is easier to program with these controls because the methods, properties, and events exposed by these controls are consistent and utilize the .NET Framework class library. In this section, I will examine the server controls that are provided by ASP.NET.
Summary of Web Form Server Controls
To access Web form controls, you need to create an ASP.NET Web application. The steps to create an ASP.NET Web application are specified in the following list:
1.Launch Visual Studio .NET.
2.Click on File. The File menu will appear.
3.On the File menu, click on New and then click on Project. The New Project dialog box will appear.
4.In the New Project dialog box, click on Visual C# projects in the Project Types list.
5.Click on ASP.NET Web Application in the Templates list and specify a name and location for the Web application in the Location text box.
6.Click on OK. A new Web application will be created.
In an ASP.NET Web application, Web form controls are available in the Toolbox. Click the View menu and select Toolbox to open Toolbox. The Web form controls are shown in Figure 19-1.
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FIGURE 19-1 Web form controls in Visual Studio .NET
As you can see, in the Toolbox, there are different categories of controls available for Web forms. These categories are described in Table 19-1.
Table 19-1 Types of Web Forms Controls
Web Forms Controls |
Description |
User controls |
User controls are used to create reusable Web pages. You use user |
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controls to create controls that are reusable across multiple Web |
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pages. For example, you can use a user control to create reusable |
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menus items, tables,toolbars, and so on. |
Validation controls |
Validation controls are used to test the values that the user |
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specifies against the requirements defined by the programmer. |
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A validation control must be associated with another control |
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that accepts user input. For example, you can use a Required- |
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FieldValidator control to check whether the user has specified |
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a value for the control. You can also use RegularExpression- |
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Validator to check for a pattern of values that is entered by |
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the user. |
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Table 19-2 Web Form Controls (continued) |
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Control |
Description |
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RadioButtonList |
Displays a list of radio buttons that allows users to select one option |
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from list of options. For example, you can use a RadioButtonList control |
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for gender, which displays two check boxes for Male and Female. |
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Calendar |
Displays a calendar and allows users to select dates and weeks. You can |
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customize the appearance of the calendar to blend it with your Web |
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application. |
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LinkButton |
A LinkButton control is similar to a Button control but it appears like a |
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hyperlink. |
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ImageButton |
Displays a button on which you can display an image. |
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HyperLink |
Used to create hyperlinks from one Web form to another. |
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Table |
Creates a table and provides several useful methods and properties to |
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render a table from the programming logic of the application. |
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Panel |
Creates a borderless division on the form that serves as a container for |
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other controls. |
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Repeater Control |
Displays information from a dataset by using a set of HTML elements |
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and controls.The Repeater control repeats the HTML elements for |
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each record in the data set. |
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DataList |
Provides extensive layout and formatting options to display information |
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in a table format.This control is similar to a Repeater control but offers |
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greater control over the format of the output. |
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DataGrid |
The DataGrid control can retrieve information from a dataset and dis - |
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play it directly on a form in the table format without requiring a user to |
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specify the structure of data in the dataset. |
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ASP.NET provides a number of validation controls that simplify your task of validating user input. Instead of coding validation logic for each control, you can use the validation controls to validate information specified by a user. The validation controls of ASP.NET are summarized in Table 19-3.
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Table 19-3 Validation Controls |
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Control |
Description |
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RequiredFieldValidator |
Ensures that users specify a valid value in the control with |
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which the RequiredFieldValidator control is associated. |
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CompareValidator |
Uses the comparison operators to validate user input with a |
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predefined value of another control or a database field. |
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RangeValidator |
Validates the user input to determine whether or not it is in |
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a predefined range for numbers, characters, or dates. |
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RegularExpressionValidator |
Matches user input with a regular expressions. For example, |
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it checks for predictable sequences of characters, such as |
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social security numbers, telephone numbers, and zip codes. |
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CustomValidator |
Checks the user’s entry by using validation logic that you |
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code for your application. |
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Working with Web Form Server Controls
Each control has a set of properties that can be used for modifying its state. You can modify the properties of a control at design time or run time.
To modify the properties of a control at design time, follow these steps:
1.Right-click on a control and select Properties. The Properties window for the control will appear. For example, the Properties window of the ListBox control is shown in Figure 19-2.
2.Change the required property of the control. For example, you can change the ID of a list box to lstMonth.
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FIGURE 19-2 The Properties window of a control
You can now modify the Items property of the list box to add months to the lstMonth control programmatically. To change the properties of a control at run time, you use the Code Editor window. Use the following steps to open the Code Editor window and change the properties of a control:
1.Drag a Button control from Toolbox to the form.
2.Double-click the button. The Code Editor window will open.
3.Add the following code to the Click event of the button.
private void Button1_Click(object sender, System.EventArgs e)
{
lstMonth.Items.Add(“January”); lstMonth.Items.Add(“February”); lstMonth.Items.Add(“March”); lstMonth.Items.Add(“April”); lstMonth.Items.Add(“May”); lstMonth.Items.Add(“June”);
