Top 10 .NET Developer Interview Questions & Answers in 2024

1. How does Dependency Injection work in ASP.NET Core, and what are the benefits of using DI in a .NET application?

Dependency Injection (DI) in ASP.NET Core is a design pattern that facilitates loose coupling between components by injecting dependencies into classes. The built-in DI container manages the lifetime and resolution of dependencies. Benefits include improved testability, modularity, and maintainability. It reduces tight coupling between components, making the codebase more flexible and easier to maintain.

2. Explain the differences between ASP.NET MVC and ASP.NET Web API. When would you choose one over the other for building web applications?

• ASP.NET MVC: Used for building web applications that follow the Model-View-Controller pattern. It's suitable for scenarios where you need to create dynamic web pages with server-side rendering.
• ASP.NET Web API: Designed for building RESTful APIs that primarily handle data and are consumed by client applications. It's suitable for scenarios where you need to expose services for client-side applications or mobile apps.

Choose ASP.NET MVC for web applications with server-side rendering and ASP.NET Web API for building APIs to serve data.

3. What is the Entity Framework, and how does Code-First development differ from Database-First development in Entity Framework?

Entity Framework (EF) is an Object-Relational Mapping (ORM) framework for .NET.

• Code-First Development: Developers define the data model using classes in code, and EF generates the database schema based on these classes. It allows for a more code-centric approach to database design.
• Database-First Development: Developers start with an existing database schema, and EF generates the corresponding classes in code. It is suitable when working with an existing database or when the database design is a priority.

4. Discuss the role of the Global.asax file in an ASP.NET application. What events can be handled in Global.asax, and provide examples of when you might use them.

The Global.asax file in ASP.NET contains application-level events and handlers. Examples include:

• Application_Start: Fired when the application starts. Useful for initializing application-wide resources.
• Session_Start: Fired when a new user session is started. Useful for session-specific initialization.
• Application_Error: Fired when an unhandled exception occurs. Useful for logging or redirecting to an error page.

These events provide hooks to execute code at key points in the application lifecycle.

5. How can you implement caching in ASP.NET applications, and what types of caching mechanisms does ASP.NET support?

ASP.NET supports various caching mechanisms:

• Output Caching: Caches the output HTML of a page. Configure it using attributes or in the web.config file.
• Data Caching: Caches data in memory. Use HttpContext.Cache to store and retrieve data.
• Fragment Caching: Caches portions of a page. Use the @OutputCache directive in Razor views.

Caching improves performance by reducing redundant processing and data retrieval.

6. Explain the concepts of ViewState and SessionState in ASP.NET. When would you choose to use ViewState, and when would you opt for SessionState?

• ViewState: Used to persist state information of a single page across postbacks. Suitable for small amounts of data and maintaining state within a page.
• SessionState: Used to persist state information across multiple requests for a user session. Suitable for larger amounts of data and maintaining state throughout a user's session.

Choose ViewState for page-specific state, and SessionState for broader user-specific state.

7. How does asynchronous programming work in .NET, and what are the advantages of using async/await in C#?

Asynchronous programming in .NET allows tasks to run concurrently, improving responsiveness.

• Async/Await: Used in C# to simplify asynchronous programming. It allows methods to be marked as asynchronous, and the await keyword is used to asynchronously wait for the completion of a task.

Advantages include improved responsiveness, reduced blocking of the main thread, and efficient utilization of resources.

8. Discuss the differences between WCF (Windows Communication Foundation) and ASP.NET Web API. When would you choose one over the other for building web services?

• WCF (Windows Communication Foundation): A comprehensive framework for building distributed systems, supporting various protocols and communication patterns. Suitable for enterprise-level services with complex requirements.
• ASP.NET Web API: Designed for building HTTP-based services using RESTful principles. Suitable for scenarios where simplicity, ease of use, and HTTP/REST are the primary considerations.

Choose WCF for complex, enterprise-level services, and ASP.NET Web API for lightweight HTTP-based services.

9. How can you secure an ASP.NET application, and what are some best practices for handling authentication and authorization?

Security measures for ASP.NET applications include:

• Authentication: Implement forms authentication, Windows authentication, or external identity providers using OAuth/OpenID.
• Authorization: Use role-based or claims-based authorization to control access to resources.
• Secure Transmission: Use HTTPS to encrypt data transmitted between the client and server.

Implement secure coding practices, validate input, and regularly update dependencies to mitigate security risks.

10. Explain the concepts of garbage collection in .NET. How does the Common Language Runtime (CLR) manage memory, and what strategies can you employ to optimize memory usage in a .NET application?

Garbage collection in .NET is the automatic process of reclaiming memory occupied by objects that are no longer in use.

• CLR Memory Management: The CLR uses a generational garbage collector with three generations: Gen0, Gen1, and Gen2. Newly created objects start in Gen0, and if they survive garbage collection, they are promoted to higher generations.
• Optimizing Memory Usage: Strategies include disposing of unmanaged resources using IDisposable, minimizing the use of finalizers, and using the using statement for resource cleanup

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Proactively manage resources to ensure efficient memory usage and minimize the impact of garbage collection on application performance.