Application and Session Events

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Introduction

Welcome to the third lesson of the Absolute Beginner's Series VWD VB, a comprehensive guide to learning Visual Web Developer 2005 Express Edition and designing and building ASP.NET Web sites. In this lesson, we will delve into the world of events and postback, exploring what they are, how they can be used in your code, and the possible responses to those events. This lesson is designed for absolute beginners, and by the end of it, you will have a solid understanding of how to handle events and work with postback in your web applications.

What are Events?

Events are actions that occur in response to user interactions or other system events. In the context of web development, events can be triggered by user actions such as clicking a button, submitting a form, or navigating to a new page. When an event occurs, it can trigger a response, such as updating a database, sending an email, or displaying a message to the user.

What are Postback?

Postback is a process that occurs when a web page is submitted to the server for processing. When a user interacts with a web page, such as clicking a button or submitting a form, the page is sent to the server for processing. The server then processes the request and sends the updated page back to the user's browser. This process is known as postback.

Handling Events in Code

In order to handle events in your code, you need to use event handlers. An event handler is a method that is called when an event occurs. You can attach an event handler to an event by using the AddHandler method. For example, you can attach an event handler to the Click event of a button control as follows:

Dim WithEvents Button1 As Button

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    ' Code to handle the button click event
End Sub

Working with Postback

When a web page is submitted to the server for processing, the server processes the request and sends the updated page back to the user's browser. You can use the IsPostBack property to determine whether the page is being posted back to the server. For example:

If Page.IsPostBack Then
    ' Code to handle the postback event
Else
    ' Code to handle the initial page load
End If

Application and Session Events

In addition to handling events on individual controls, you can also handle events at the application and session levels. Application events occur when the application starts or stops, while session events occur when a user logs in or out. You can handle these events by using the Application_Start and Application_End methods in the global.asax file.

Protected Sub Application_Start(sender As Object, e As EventArgs)
    ' Code to handle the application start event
End Sub

Protected Sub Application_End(sender As Object, e As EventArgs)
    ' Code to handle the application end event
End Sub

Conclusion

In this lesson, we have explored the world of events and postback, learning how to handle events in code, work with postback, and handle application and session events. By the end of this lesson, you should have a solid understanding of how to handle events and work with postback in your web applications.

Practice Exercises

To reinforce your understanding of the concepts covered in this lesson, try the following practice exercises:

Create a new web page and add a button control to it.
Attach an event handler to the button's Click event.
Use the IsPostBack property to determine whether the page is being posted back to the server.
Handle application and session events in the global.asax file.

Solution

The solution to the practice exercises can be found in the 03 VWD VB Study Guide Solution.wmv file, which is included in the lesson materials.

Lesson Materials

The lesson materials include the following files:

03 VWD VB Lesson.wmv: A 17-minute Windows Media Video file with the lesson itself.
03 VWD VB Lesson Transcript: A 7-page Microsoft Word document with the video transcription.
EULA.ftr: A Rich Text Format document containing license information.
03 VWD VB Study Guide.pdf: A 3-page PDF document containing a few guidelines and instructions about the lesson and some exercises to apply what was learned.
03 VWD VB Study Guide Solution.wmv: A 20-minute Windows Media Video file containing the solution for the study guide.
03 VWD VB Code: A subfolder containing some auxiliary files needed to execute the practice.

Prerequisites

Before taking this lesson, you should have a basic understanding of Visual Web Developer 2005 Express Edition and ASP.NET Web sites. You should also have the Visual Web Developer 2005 Express Edition installed on your computer.

Conclusion

Q: What is an event in the context of web development?

A: An event is an action that occurs in response to user interactions or other system events. In the context of web development, events can be triggered by user actions such as clicking a button, submitting a form, or navigating to a new page.

Q: What is postback?

A: Postback is a process that occurs when a web page is submitted to the server for processing. When a user interacts with a web page, such as clicking a button or submitting a form, the page is sent to the server for processing. The server then processes the request and sends the updated page back to the user's browser.

Q: How do I handle events in code?

A: To handle events in code, you need to use event handlers. An event handler is a method that is called when an event occurs. You can attach an event handler to an event by using the AddHandler method. For example, you can attach an event handler to the Click event of a button control as follows:

Dim WithEvents Button1 As Button

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    ' Code to handle the button click event
End Sub

Q: How do I determine whether a page is being posted back to the server?

A: You can use the IsPostBack property to determine whether a page is being posted back to the server. For example:

If Page.IsPostBack Then
    ' Code to handle the postback event
Else
    ' Code to handle the initial page load
End If

Q: What are application and session events?

A: Application events occur when the application starts or stops, while session events occur when a user logs in or out. You can handle these events by using the Application_Start and Application_End methods in the global.asax file.

Protected Sub Application_Start(sender As Object, e As EventArgs)
    ' Code to handle the application start event
End Sub

Protected Sub Application_End(sender As Object, e As EventArgs)
    ' Code to handle the application end event
End Sub

Q: How do I handle application and session events?

A: To handle application and session events, you need to use the Application_Start and Application_End methods in the global.asax file. You can also use the Session_Start and Session_End methods to handle session events.

Protected Sub Session_Start(sender As Object, e As EventArgs)
    ' Code to handle the session start event
End Sub

Protected Sub Session_End(sender As Object, e As EventArgs)
    ' Code to handle the session end event
End Sub

Q: What are some common events that occur in web development?

A: Some common events that occur in web development include:

Button click events
Form submission events
Page load events
Application start and end events
Session start and end events

Q: How do I debug events in my code?

A: To debug events in your code, you can use the Visual Studio debugger to step through your code and see where the events are being triggered. You can also use the Debug.WriteLine method to write debug information to the console.

Q: What are some best practices for handling events in my code?

A: Some best practices for handling events in your code include:

Using event handlers to handle events
Using the IsPostBack property to determine whether a page is being posted back to the server
Handling application and session events in the global.asax file
Using the Debug.WriteLine method to write debug information to the console

Conclusion

In conclusion, this Q&A article has provided you with a comprehensive overview of events and postback in Visual Web Developer 2005 Express Edition. By following the best practices outlined in this article, you can write more efficient and effective code that handles events and postback correctly.