ASP.NET - Event Handling

In ASP.NET, event handling refers to the ability to respond to user actions such as clicking a button or selecting an item in a dropdown list. Events in ASP.NET are handled using event handlers, which are methods that execute in response to a specific event.

Here's an example of how to create an event handler for a button click event in ASP.NET:

  • Open your ASP.NET project in Visual Studio.
  • Double-click on the button control in the design view of the page to open the code-behind file for the page.
  • In the code-behind file, add a method with the following signature:

protected void Button1_Click(object sender, EventArgs e)

{

    // Code to handle the button click event goes here

}

  • Inside the method, add the code to handle the button click event. For example, you could display a message to the user or perform some other action.
  • Save the code-behind file and run the application to test the button click event.

Note that the method name (Button1_Click) is created automatically by Visual Studio when you double-click on the button control in the design view of the page. You can change the name of the method if you want, but you also need to update the event handler for the button control in the ASPX page to point to the new method name.

In ASP.NET, the Application and Session objects are used to store data that can be accessed by multiple pages in the application. These objects raise events that you can handle to perform specific actions when certain events occur.

The Application object represents the entire ASP.NET application and provides a way to share data across all users and sessions. The following are some of the Application events:

  • Application_Start: This event is raised when the application starts for the first time or is restarted after being stopped.
  • Application_End: This event is raised when the application is shut down, either by the server or by calling the Stop method of the Application object.
  • Application_Error: This event is raised when an unhandled exception occurs in the application.

To handle Application events, you can add event handler methods to the Global.asax file of your ASP.NET application. Here's an example of how to handle the Application_Start event:

void Application_Start(object sender, EventArgs e)

{

    // Code to run when the application starts

}

The Session object represents a specific user session in the ASP.NET application and provides a way to store data that is specific to that session. The following are some of the Session events:

  • Session_Start: This event is raised when a new user session is started.
  • Session_End: This event is raised when a user session is ended, either by the server or by the user closing their browser.

To handle Session events, you can add event handler methods to the Global.asax file of your ASP.NET application. Here's an example of how to handle the Session_Start event:

void Session_Start(object sender, EventArgs e)

{

    // Code to run when a new user session is started

}

Some of the most common events of controls in ASP.NET and their descriptions:

  1. Click event: This event is raised when a button or link button control is clicked by the user.
  2. SelectedIndexChanged event: This event is raised when the selected item in a drop-down list, list box, or radio button list control is changed.
  3. TextChanged event: This event is raised when the text in a text box control is changed.
  4. DataBound event: This event is raised after data is bound to a data-bound control, such as a GridView or Repeater control.
  5. RowDataBound event: This event is raised for each row in a data-bound control and allows you to customize the appearance or behavior of each row.
  6. ItemCommand event: This event is raised when a command is issued by a control, such as a button or link button, inside a data-bound control.
  7. Page_Load event: This event is raised when the page is loaded or reloaded, and is commonly used to initialize the page and load data.
  8. Page_Init event: This event is raised when the page is initialized, and is commonly used to set up the page's controls and properties.
  9. Page_PreRender event: This event is raised just before the page is rendered to the browser, and is commonly used to perform final formatting or processing of the page.
  10. Page_Unload event: This event is raised when the page is unloaded, and is commonly used to release any resources or clean up any state that was used by the page.

These are just a few examples of the most common events of controls in ASP.NET. Depending on the control and its purpose, there may be other events available as well. Understanding these events and how to use them effectively can be a key part of developing effective and responsive web applications.