MSDN Documentation

ASP.NET Pages

Understanding ASP.NET Pages

ASP.NET Pages are the fundamental building blocks for creating dynamic web applications. They provide a robust framework for handling user requests, processing data, and rendering HTML output.

The ASP.NET page model abstracts much of the complexity of web development, allowing developers to focus on application logic rather than low-level HTTP protocols. This is achieved through:

  • Server-side Code: Logic is executed on the server, typically written in C# or VB.NET.
  • Client-side Rendering: The server generates HTML, CSS, and JavaScript which is then sent to the client's browser.
  • Event-driven Model: Pages respond to user interactions and server events in a manner similar to desktop applications.
The core idea behind ASP.NET Pages is to leverage a familiar programming model for web development, making it accessible to a wide range of developers.

Key Components of an ASP.NET Page

An ASP.NET Page consists of several key components:

  • Code-Behind File (.aspx.cs or .aspx.vb): Contains the server-side C# or VB.NET code that defines the page's behavior and logic.
  • Markup File (.aspx): Defines the structure and appearance of the page using HTML and ASP.NET server controls.
  • Directives: Special instructions at the top of the page that configure how the page is processed (e.g., <%@ Page ... %>).
  • Server Controls: UI elements that can be manipulated programmatically on the server (e.g., <asp:Button ... />, <asp:TextBox ... />).
  • Events: Methods that handle user actions or system events (e.g., Page_Load, Button_Click).

Page Lifecycle

ASP.NET Pages follow a well-defined lifecycle for each request. Understanding this lifecycle is crucial for proper event handling and data management:

  1. Page Request
  2. Page Initialization
  3. Loading State
  4. Event Validation
  5. Data Binding
  6. Rendering
  7. Unloading

Example: A Simple ASP.NET Page

Here's a basic example demonstrating a server control and an event handler:

Markup File (Default.aspx)

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>



    <title>My ASP.NET Page</title>


    <form id="form1" runat="server">
        <div>
            <asp:Label ID="lblMessage" runat="server" Text="Enter your name:"></asp:Label>
            <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
            <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />
            <asp:Label ID="lblGreeting" runat="server" />
        </div>
    </form>

Code-Behind File (Default.aspx.cs)

using System;
using System.Web.UI;

public partial class _Default : Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // Initialize controls on first load
            lblGreeting.Text = "";
        }
    }

    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        string userName = txtName.Text;
        lblGreeting.Text = $"Hello, {userName}!";
    }
}

Further Reading