MSDN Documentation

• Overview
• Data Access
• ASP.NET
  • Introduction
  • Pages
  • Controls
  • Data Binding
  • State Management
• Web Services

ASP.NET Controls

ASP.NET controls are the building blocks for creating dynamic and interactive web pages. They abstract away the complexities of HTML and HTTP, allowing developers to focus on application logic.

Introduction to ASP.NET Controls

ASP.NET introduces a rich set of server controls that can be placed on a web form. These controls render as standard HTML elements on the client browser but are managed on the server. This server-side management allows for features like event handling, data binding, and view state.

Controls can be categorized into several types:

• HTML Server Controls: These controls directly map to standard HTML elements (e.g., <input>, <a>) and have server-side equivalents (e.g., HtmlInputText, HtmlAnchor). They offer direct manipulation of HTML attributes.
• Web Server Controls: These are higher-level controls that provide more functionality and abstract away HTML rendering. Examples include Label, Button, TextBox, DropDownList, and GridView. They offer properties and events that simplify common web development tasks.
• Data Controls: Specifically designed for displaying and manipulating data, such as GridView, DetailsView, and FormView.
• Validation Controls: Used to validate user input before it's submitted to the server, including RequiredFieldValidator, CompareValidator, and RegularExpressionValidator.
• Navigation Controls: Help in creating navigation structures, like Menu and SiteMapDataSource.
• Authentication and Authorization Controls: Facilitate user login and access control.

Web Server Controls

Web server controls are the most commonly used type. They are declared in the .aspx file using a special syntax:

<asp:Label ID="WelcomeLabel" runat="server" Text="Hello, World!" />
<asp:Button ID="SubmitButton" runat="server" Text="Submit" OnClick="SubmitButton_Click" />

The <asp:...> prefix indicates an ASP.NET server control. The runat="server" attribute is crucial, as it tells the ASP.NET runtime to process this element on the server. The ID attribute provides a unique identifier for the control, allowing it to be referenced in server-side code.

Common Web Server Controls

protected void SubmitButton_Click(object sender, EventArgs e)
{
    string userInput = NameTextBox.Text;
    WelcomeLabel.Text = $"Hello, {userInput}!";
    Response.Write($"User entered: {userInput}");
}

View State

View state is a mechanism used by ASP.NET to maintain the state of controls across multiple requests. When a postback occurs (a request from the client to the server generated by a control event like a button click), view state allows the server to restore the control's properties to their values from the previous request. This is typically implemented by embedding a hidden field in the HTML page that contains the serialized state of the controls.

Control Lifecycle

ASP.NET controls go through a well-defined lifecycle on the server during each request. Understanding this lifecycle is crucial for writing robust applications. Key events include:

• Initialization: Controls are created and initialized.
• Load: View state is loaded, and control properties are set.
• Postback Data Processing: If the control is an input control, its posted data is processed.
• Event Handling: If an event occurred on the client and was posted back, the corresponding event handler is executed.
• Pre-Render: Controls are prepared for rendering.
• Render: The control generates its HTML output.
• Unload: Controls are cleaned up.

Custom Controls

ASP.NET also supports the creation of custom controls. This allows developers to encapsulate reusable UI components with specific functionality, extending the built-in control library. Custom controls can be user controls (composed of existing controls) or custom server controls (written from scratch in code).