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## ASP.NET Web Control: CheckBox Checked Property The `Checked` property is a fundamental property of the ASP.NET Web Server `CheckBox` control. It is used to get or set a value indicating whether the `CheckBox` control is selected (checked). --- ## Definition and Usage The `Checked` property determines the state of the `CheckBox` control: * When set to `true`, the checkbox is checked (selected). * When set to `false`, the checkbox is unchecked (cleared). By default, the `Checked` property is set to `false`. --- ## Syntax You can declare the `Checked` property declaratively in your `.aspx` markup or programmatically in your code-behind (C# or VB.NET). ### Declarative Syntax ```xml ``` ### Programmatic Syntax (C#) ```csharp // Get the state of the checkbox bool isChecked = myCheckBox.Checked; // Set the state of the checkbox myCheckBox.Checked = true; ``` --- ## Code Examples ### Example 1: Basic Declarative Usage The following example demonstrates how to pre-check a `CheckBox` control when the page loads for the first time. ```xml

``` ### Example 2: Interactive Code-Behind Example This example shows how to read the state of the `Checked` property during a postback event (e.g., when a button is clicked) and display a message to the user. #### ASPX Markup (`Default.aspx`): ```xml <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="YourApp.Default" %>

Newsletter Subscription

``` #### Code-Behind (`Default.aspx.cs`): ```csharp using System; namespace YourApp { public partial class Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { // Optional: Initialize checkbox state on initial page load if (!IsPostBack) { lblMessage.Text = "Please make a selection."; } } protected void btnSubmit_Click(object sender, EventArgs e) { // Check the state of the Checked property if (chkSubscribe.Checked) { lblMessage.Text = "Thank you! You have successfully subscribed to our newsletter."; lblMessage.ForeColor = System.Drawing.Color.Green; } else { lblMessage.Text = "You opted out of the newsletter subscription."; lblMessage.ForeColor = System.Drawing.Color.Red; } } } } ``` --- ## Key Considerations 1. **AutoPostBack Interaction**: By default, changing the checked state of a checkbox on the client side does not immediately trigger a postback to the server. If you want the server-side code to execute immediately when a user clicks the checkbox, you must set the `AutoPostBack` property to `true` and handle the `OnCheckedChanged` event. 2. **State Persistence**: The state of the `Checked` property is automatically maintained across postbacks using ASP.NET ViewState, provided ViewState is enabled for the control or page. 3. **Boolean Values in Markup**: In the `.aspx` markup, the `Checked` attribute accepts string representations of booleans (e.g., `"true"`, `"false"`, `"TRUE"`, or `"FALSE"`). In the C# code-behind, it strictly requires a boolean type (`true` or `false`).