Asp.Net Mvc Role Of Global Asax Complete Guide

Here's a step-by-step guide with complete examples to help you understand and utilize Global.asax in your ASP.NET MVC applications.

Step 1: Understanding the Basic Structure

When you create a new ASP.NET MVC project, you might see a Global.asax file or the Global.asax.cs class. This class is derived from HttpApplication and is used to define methods that handle events raised by ASP.NET at the application level.

Global.asax

<%@ Application Codebehind="Global.asax.cs" Inherits="MyMvcApp.MvcApplication" Language="C#" %>

Global.asax.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;
using MyMvcApp.Models;

namespace MyMvcApp
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            RouteConfig.RegisterRoutes(RouteTable.Routes);
        }
    }
}

Step 2: Handling Different Events

Now let's add some basic event handlers in Global.asax.cs.

Example: Logging Application Start and End

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;
using MyMvcApp.Models;

namespace MyMvcApp
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            // Log the start of the application
            System.Diagnostics.Debug.WriteLine("Application Started");

            AreaRegistration.RegisterAllAreas();
            RouteConfig.RegisterRoutes(RouteTable.Routes);
        }

        protected void Application_End()
        {
            // Log the end of the application
            System.Diagnostics.Debug.WriteLine("Application Ended");
        }

        protected void Session_Start(object sender, EventArgs e)
        {
            // Log when a session starts
            System.Diagnostics.Debug.WriteLine("Session Started");

            // Optionally, initialize the session here
            HttpContext.Current.Session["StartTime"] = DateTime.Now;
        }

        protected void Session_End(object sender, EventArgs e)
        {
            // Log when a session ends
            System.Diagnostics.Debug.WriteLine("Session Ended");
        }
    }
}

Step 3: Adding Custom Error Handling

One of the common uses of Global.asax is for handling unhandled exceptions globally.

Example: Custom Error Handling

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;
using MyMvcApp.Models;

namespace MyMvcApp
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            System.Diagnostics.Debug.WriteLine("Application Started");

            AreaRegistration.RegisterAllAreas();
            RouteConfig.RegisterRoutes(RouteTable.Routes);

            // Register global exception handler
            this.BeginRequest += BeginRequestHandler;
            this.EndRequest += EndRequestHandler;
        }

        void BeginRequestHandler(object sender, EventArgs e)
        {
            System.Diagnostics.Debug.WriteLine("Request Started");
        }

        void EndRequestHandler(object sender, EventArgs e)
        {
            if (HttpContext.Current.Response.StatusCode == 500)
            {
                Exception exception = Server.GetLastError();
                System.Diagnostics.Debug.WriteLine($"Error occurred: {exception.Message}");

                // Clear error from server so we can redirect to our custom error page
                Server.ClearError();

                // Redirect user to custom error page
                Response.Redirect("~/Home/Error");
            }
        }

        protected void Application_End()
        {
            System.Diagnostics.Debug.WriteLine("Application Ended");
        }

        protected void Session_Start(object sender, EventArgs e)
        {
            System.Diagnostics.Debug.WriteLine("Session Started");
            HttpContext.Current.Session["StartTime"] = DateTime.Now;
        }

        protected void Session_End(object sender, EventArgs e)
        {
            System.Diagnostics.Debug.WriteLine("Session Ended");
        }
    }
}

In this example:

• We added two event handlers for request start and end.
• If an unhandled exception occurs, we log it, clear the last error, and redirect the user to a custom error page (~/Home/Error).

Step 4: Creating a Custom Error Page

Now, let's create the custom error page that we'll redirect to in the case of an error.

HomeController

First, add an action method called Error in your HomeController:

using System.Web.Mvc;

namespace MyMvcApp.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult Error()
        {
            ViewBag.ErrorMessage = "An unexpected error occurred.";
            return View();
        }
    }
}

Error.cshtml

Create a view Error.cshtml inside the Views/Home folder:

@{
    ViewBag.Title = "Error";
}

<h2>@ViewBag.Title</h2>
<p>@ViewBag.ErrorMessage</p>

Step 5: Configuring Web.config for Custom Errors

To make sure that your application uses the custom error pages, you need to configure the web.config file.

web.config

Add or modify the <customErrors> section in your web.config:

<configuration>
  <system.web>
    <!-- other configurations -->
    <customErrors mode="On" defaultRedirect="~/Home/Error">
      <error statusCode="404" redirect="~/Home/NotFound" />
      <error statusCode="500" redirect="~/Home/Error" />
    </customErrors>
  </system.web>
</configuration>

This configuration enables custom error redirecting and specifies a default URL for general errors (500). You can also specify different URLs for specific HTTP status codes like 404.

Step 6: Testing Your Custom Errors

To test the custom error page, you can deliberately cause an error in one of your controllers. For example:

HomeController

Add another action method to simulate a runtime error:

public ActionResult CauseError()
{
    throw new Exception("This is a test error.");
}

Navigate to this action (/Home/CauseError) and you should be redirected to the Error view with the message "An unexpected error occurred."

Conclusion

The Global.asax file serves as a key entry point for controlling the lifecycle events of your ASP.NET MVC application. By handling events like application start, end, session start, end, and request errors, you can perform crucial tasks such as application initialization, logging, and error handling.