11. How would you handle errors and exceptions in an MVC application to provide a good user experience?

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11. How would you handle errors and exceptions in an MVC application to provide a good user experience?

Overview

Handling errors and exceptions in an MVC application is crucial for maintaining a smooth and secure user experience. Effective error handling not only prevents the application from crashing but also provides meaningful feedback to the user, potentially logging useful information for developers to address the underlying issues. This section explores techniques for managing errors and exceptions in MVC applications, emphasizing the importance of a well-structured approach to enhance usability and reliability.

Key Concepts

  1. Global Error Handling - Implementing application-wide error handling using custom error pages and global filters.
  2. Exception Filters - Utilizing exception filters to catch and handle errors locally within controllers or globally across the application.
  3. Logging and Diagnostics - Implementing logging mechanisms to record exceptions and application behavior, facilitating debugging and monitoring.

Common Interview Questions

Basic Level

  1. How do you create a custom error page in MVC?
  2. What is the purpose of the HandleError attribute in MVC?

Intermediate Level

  1. How can you implement global error handling in an MVC application?

Advanced Level

  1. Discuss strategies for logging and handling errors in a high-traffic MVC application.

Detailed Answers

1. How do you create a custom error page in MVC?

Answer: Creating a custom error page in MVC involves configuring the Web.config file and adding specific views for different error codes. This approach allows developers to provide a better user experience during exceptions, by displaying user-friendly error messages instead of generic server error pages.

Key Points:
- The customErrors mode must be set to "On" or "RemoteOnly" in the Web.config file.
- Specific error status codes (like 404) can be handled by adding corresponding views in the Views\Shared folder (e.g., Error404.cshtml).
- The Application_Error method in Global.asax can be used for logging and redirecting to a generic error page.

Example:

// Web.config configuration
<configuration>
    <system.web>
        <customErrors mode="On" defaultRedirect="~/Error">
            <error statusCode="404" redirect="~/Error/NotFound"/>
        </customErrors>
    </system.web>
</configuration>

// Global.asax Application_Error
protected void Application_Error(object sender, EventArgs e)
{
    // Logic to handle global errors, logging, etc.
}

2. What is the purpose of the HandleError attribute in MVC?

Answer: The HandleError attribute in MVC is a filter that provides a way to gracefully handle unhandled exceptions thrown during the execution of action methods. It can redirect the user to a specified view, allowing for a custom error response instead of breaking the application flow.

Key Points:
- Can be applied globally or to specific controllers/actions.
- Allows specifying the type of exceptions to handle.
- Works only for exceptions thrown in the MVC pipeline.

Example:

[HandleError(View = "ErrorView", ExceptionType = typeof(InvalidOperationException))]
public class HomeController : Controller
{
    public ActionResult Index()
    {
        throw new InvalidOperationException("Example exception");
    }
}

3. How can you implement global error handling in an MVC application?

Answer: Global error handling in MVC can be achieved by using filters and the Application_Error method in Global.asax. A global filter can catch exceptions thrown by any action method across controllers, while Application_Error can handle exceptions outside the MVC pipeline.

Key Points:
- Use the GlobalFilters collection to add the HandleErrorAttribute.
- Configure customErrors in Web.config.
- Utilize Application_Error for exceptions not caught by MVC filters.

Example:

// Global.asax
public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        // Register global filters
        GlobalFilters.Filters.Add(new HandleErrorAttribute());
    }

    protected void Application_Error(object sender, EventArgs e)
    {
        // Global error handling logic
    }
}

4. Discuss strategies for logging and handling errors in a high-traffic MVC application.

Answer: In high-traffic MVC applications, efficient logging and error handling are critical for maintaining performance and identifying issues quickly. Strategies include asynchronous logging, using robust logging frameworks, and implementing a centralized error handling mechanism.

Key Points:
- Implement asynchronous logging to avoid blocking the main application thread.
- Use logging frameworks like NLog or Serilog for comprehensive logging capabilities.
- Consider a centralized exception management system to handle and log errors uniformly across the application.

Example:

public class ErrorHandler : HandleErrorAttribute
{
    public override void OnException(ExceptionContext filterContext)
    {
        LogException(filterContext.Exception);
        base.OnException(filterContext);
    }

    private void LogException(Exception exception)
    {
        // Asynchronous logging to an external system
        Task.Run(() => Logger.Log(exception));
    }
}

This guide covers the essentials of handling errors and exceptions in MVC applications, from basic custom error pages to advanced logging strategies, providing a solid foundation for managing errors effectively and improving the user experience.

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