Interview Questions and Answers on ASP.NET ( 2025 )
Some common interview questions and answers related to ASP.NET, which may help you prepare for your interview.
Basic Questions
1. What is ASP.NET?
- Answer: ASP.NET is an open-source web framework developed by Microsoft for building modern web applications and services. It allows developers to build dynamic websites, web applications, and web services.
2. What is the difference between ASP.NET Web Forms and ASP.NET MVC?
- Answer:
- ASP.NET Web Forms is a component-based framework where developers interact with server-side controls using event-driven programming.
- ASP.NET MVC (Model-View-Controller), on the other hand, is a design pattern that separates the application into three main components: Models, Views, and Controllers, promoting better organization and maintainability of code.
3. What is a ViewState in ASP.NET?
- Answer: ViewState is a mechanism that maintains the state of the server-side controls during postbacks. It stores the values of these controls in a hidden field on the page, allowing them to maintain their values between requests.
Intermediate Questions
4. What is the difference between Server.Transfer and Response.Redirect?
- Answer:
- Server.Transfer transfers execution to a different page on the server without making a round trip back to the client's browser, preserving the original URL in the browser.
- Response.Redirect sends a response back to the client's browser to make a new request to a different page, updating the URL in the browser.
5. What is the role of Global.asax in ASP.NET?
- Answer: Global.asax, also known as the application file, is used to handle application-level events such as Application_Start, Application_End, Session_Start, and Session_End. It provides a way to execute code on specific events during the lifecycle of the application.
6. What are ActionFilters in ASP.NET MVC?
- Answer: ActionFilters are attributes that allow you to execute code before and after an action method executes. They can be used for cross-cutting concerns like logging, authentication, or authorization. Common filters include `ActionFilterAttribute`, `AuthorizeAttribute`, and `OutputCache`.
Advanced Questions
7. What is Dependency Injection in ASP.NET Core?
- Answer: Dependency Injection (DI) is a design pattern used to implement Inversion of Control (IoC) in which a class receives its dependencies from an external source rather than creating them internally. ASP.NET Core has built-in DI support, allowing services to be registered in the `ConfigureServices` method, and can be injected into controllers and other classes.
8. What is ASP.NET Web API?
- Answer: ASP.NET Web API is a framework that makes it easy to build HTTP services that can be accessed by a variety of clients, such as browsers, mobile devices, and desktop applications. It follows RESTful principles, allowing CRUD (Create, Read, Update, Delete) operations to be performed.
9. How do you handle exceptions in ASP.NET MVC?
- Answer: Exceptions in ASP.NET MVC can be handled using several methods:
- Using the `try-catch` block to catch exceptions within action methods.
- Implementing a custom error page in the `web.config` file.
- Using the `Application_Error` method in `Global.asax`.
- Creating a custom exception filter by inheriting from `FilterAttribute` and implementing `OnException`.
Miscellaneous Questions
10. What are Tag Helpers in ASP.NET Core?
- Answer: Tag Helpers are a new feature in ASP.NET Core that enable server-side code to participate in rendering HTML elements in Razor views. They allow developers to use HTML-like syntax to create dynamic content without relying heavily on raw HTML tags or helper methods.
11. What is the purpose of the `appsettings.json` file in ASP.NET Core?
- Answer: The `appsettings.json` file is used to store configuration settings in a structured JSON format in ASP.NET Core applications. It can include application settings, connection strings, and other key-value pairs that can be accessed via the configuration system.
12. What is Razor?
- Answer: Razor is a markup syntax used in ASP.NET to create dynamic web pages. It allows you to embed server-side code into HTML using the `@` symbol, which makes it easier to work with server-side logic directly within HTML views.
Conclusion
Preparing for an ASP.NET interview should include a solid understanding of both fundamental and advanced topics. Make sure to supplement your preparation with hands-on coding exercises and building sample projects to practically apply what you learn. Good luck!
Advance Interview Questions and Answers on ASP.NET (2025)
Some advanced interview questions along with their explanations and answers related to ASP.NET. These can help you prepare for interviews focused on ASP.NET.
1. What are Asynchronous Controllers in ASP.NET?
Answer:
Asynchronous controllers in ASP.NET allow you to handle requests without blocking the server thread. This is particularly useful for I/O-bound operations, such as accessing a database or calling an external web service. By using the `async` and `await` keywords, you can significantly improve the scalability of your application.
Example:
```csharp
public async Task<ActionResult> GetDataAsync()
{
var data = await _database.GetDataAsync();
return View(data);
}
```
2. Explain the ASP.NET MVC Request Life Cycle.
Answer:
The ASP.NET MVC request life cycle consists of several steps:
1. Routing: The routing module matches the incoming request to a route defined in the RouteConfig.
2. Controller Initialization: The MVC framework instantiates the controller based on the route data.
3. Action Execution: The framework searches for the appropriate action method and executes it.
4. Result Execution: The action can return different types of results (ViewResult, JsonResult, etc.), which are processed by the framework.
5. View Engine: If the result is a view, the framework looks for a view file using the registered view engines.
6. Response: The response is sent back to the client.
3. Describe Dependency Injection in ASP.NET Core.
Answer:
Dependency Injection (DI) is a technique where an object receives its dependencies from an external source rather than creating them internally. ASP.NET Core has built-in support for DI through the `IServiceCollection` interface, allowing you to register services in `Startup.cs`.
Example:
```csharp
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<IMyService, MyService>();
}
```
Then, you can inject this service into your controllers or other classes via constructor injection:
```csharp
public class MyController : Controller
{
private readonly IMyService _myService;
public MyController(IMyService myService)
{
_myService = myService;
}
}
```
4. What is Middleware in ASP.NET Core?
Answer:
Middleware is software that is assembled into an application pipeline to handle requests and responses. Each component (middleware) can process the HTTP request and optionally pass it to the next middleware in the pipeline. Middleware can perform tasks such as authentication, logging, error handling, and more.
Example of creating a middleware:
```csharp
public class CustomMiddleware
{
private readonly RequestDelegate _next;
public CustomMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task InvokeAsync(HttpContext context)
{
// Do something before the request
await _next(context); // Call the next middleware in the pipeline
// Do something after the request
}
}
// Register in Startup.cs
public void Configure(IApplicationBuilder app)
{
app.UseMiddleware<CustomMiddleware>();
}
```
5. Explain the differences between MVC and Web API in ASP.NET.
Answer:
- Purpose: MVC is used to build web applications with HTML view generation, while Web API is designed for building RESTful services and typically returns data in JSON or XML format.
- Request Handling: MVC uses actions to return views, Web API uses actions to return data.
- Routing: Web API uses attribute-based routing more extensively whereas MVC typically uses conventional routing.
- Content Negotiation: Web API supports content negotiation, allowing clients to request formats like JSON or XML, while MVC is primarily concerned with returning HTML views.
6. What is ViewState, and how does it work in ASP.NET Web Forms?
Answer:
ViewState is a mechanism ASP.NET Web Forms uses to preserve page and control values between postbacks. It stores the state of controls in a hidden field on the page. When the page is posted back to the server, this hidden field is sent along with the request, allowing the server to reconstruct the state of the page.
While ViewState encapsulates state management for dynamic pages, its size can bloat the HTML and affect performance. Proper use of ViewState includes disabling it for controls that do not require state management.
7. What are the different types of caching in ASP.NET?
Answer:
ASP.NET supports several types of caching:
- Output Caching: Caches the dynamic page output. You can use the `[OutputCache]` attribute to specify caching.
- Data Caching: Stores application data in memory. You can use the `Cache` object to store data that will be reused across requests and sessions.
- Application Caching: Stores application-wide data that is shared across all users.
- Distributed Caching: Uses external systems like Azure Cache or Redis for caching in a distributed environment.
8. What are Exception Filters in ASP.NET Web API?
Answer:
Exception filters are a type of filter in ASP.NET Web API that provide a way to handle exceptions globally or at the action/controller level. They allow developers to intercept exceptions thrown as a result of processing a web request, typically for logging or modifying the response sent to the client.
Example:
```csharp
public class MyExceptionFilter : ExceptionFilterAttribute
{
public override void OnException(HttpActionExecutedContext context)
{
// Log the exception or modify the response
context.Response = new HttpResponseMessage(HttpStatusCode.InternalServerError)
{
Content = new StringContent("An error occurred")
};
}
}
```
9. How does ASP.NET Core support Cross-Origin Resource Sharing (CORS)?
Answer:
CORS is a security feature that allows or restricts resources requested from a different domain. In ASP.NET Core, you can enable CORS by using the `Microsoft.AspNetCore.Cors` package and configure it in the `Startup.cs`.
Example:
```csharp
public void ConfigureServices(IServiceCollection services)
{
services.AddCors(options =>
{
options.AddPolicy("AllowAllOrigins", builder =>
builder.AllowAnyOrigin()
.AllowAnyMethod()
.AllowAnyHeader());
});
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseCors("AllowAllOrigins");
}
```
10. What is the purpose of Entity Framework (EF) in ASP.NET applications?
Answer:
Entity Framework is an Object-Relational Mapping (ORM) framework for .NET applications. It simplifies data access by allowing developers to work with databases using .NET objects rather than raw database queries. You can interact with the database using LINQ and retrieve data in a strongly typed manner. EF supports various database operations like Create, Read, Update, and Delete (CRUD), managing relationships, migrations, and more.
These questions cover various aspects of ASP.NET, including MVC, Web API, Entity Framework, and core principles of application design. Make sure you understand the concepts behind these answers as they may be expanded upon during the interview. Good luck!
Top Web API Interview Questions and Answers (2025)
1. What is a Web API?
Answer:
A Web API is an application programming interface for either a web server or a web browser. It provides access to services via HTTP protocols, typically using REST architecture.
2. What is REST in Web API?
Answer:
REST (Representational State Transfer) is an architectural style that uses standard HTTP methods (GET, POST, PUT, DELETE) for communication. It's stateless and resource-based.
3. What are HTTP methods used in Web API?
Answer:
GET: Retrieve dataPOST: Create new dataPUT: Update existing dataDELETE: Remove dataPATCH: Partially update dataAnswer:
REST: Lightweight, uses HTTP, supports JSON and XML, stateless.
SOAP: Heavier, uses XML only, includes built-in security and transaction support.
5. What is routing in Web API?
Answer:
Routing is the mechanism to map HTTP requests to the corresponding controller and action methods. In ASP.NET Web API, routes are defined using attribute routing or convention-based routing.
6. What is the difference between ASP.NET MVC and Web API?
Answer:
ASP.NET MVC is for building web applications with HTML views. Web API is used for building RESTful services to be consumed by clients like mobile apps or front-end frameworks.
7. How do you secure a Web API?
Answer:
Authentication: Token-based (JWT, OAuth)
Authorization: Role-based or claims-based
HTTPS: Secure the communication
CORS policies: Protect from cross-origin attacks
8. What is CORS in Web API?
Answer:
CORS (Cross-Origin Resource Sharing) allows or restricts resources on a web page to be requested from another domain. It’s configured via middleware in .NET Core or through attributes in classic Web API.
9. Explain Dependency Injection in Web API.
Answer:
Dependency Injection (DI) is a design pattern used to achieve Inversion of Control (IoC) between classes and their dependencies. ASP.NET Core has built-in support for DI, enabling better testing and modular code.
Answer:
Using try-catch blocks in controllers
Implementing custom
ExceptionFilterAttribute
Global exception handling
using middleware or filtersQ . What is Authentication and Authorization in ASP.NET?
Authentication:
The process of verifying the identity of a user. ASP.NET supports:
· Cookie-based Authentication
· JWT (JSON Web Token) Authentication
· OAuth2 and OpenID Connect
· ASP.NET Core Identity
Authorization:
Determines what an authenticated user is allowed to do. Supports:
· Role-Based Authorization
· Policy-Based Authorization
· Claims-Based Authorization
· Custom Authorization Handlers
1. Cookie Authentication (ASP.NET MVC & Core)
Used for traditional web apps:
services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme) .AddCookie();2. JWT Bearer Authentication (Web APIs)
Used for SPAs or mobile apps:
services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme) .AddJwtBearer(options => { options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ... }; });3. ASP.NET Core Identity
Full membership system with support for user registration, password hashing, 2FA, etc.
Role-Based Authorization Example
[Authorize(Roles = "Admin")]public IActionResult AdminDashboard() => View();Policy-Based Authorization Example
services.AddAuthorization(options =>{ options.AddPolicy("OnlyHR", policy => policy.RequireClaim("Department", "HR"));}); [Authorize(Policy = "OnlyHR")]public IActionResult HRPage() => View();Claims-Based Authorization
· Claims represent user-specific data (e.g., email, department).
· Useful when roles are not flexible enough.
var claims = new List<Claim> { new Claim(ClaimTypes.Name, "John"), new Claim("Department", "Finance")};Authentication vs Authorization – Key Differences
|
Feature |
Authentication |
Authorization |
|
Purpose |
Validates user identity |
Grants access to resources |
|
When it happens |
Before authorization |
After successful authentication |
|
Examples |
Login with username/password |
Admin-only page access |
Best Practices for Secure ASP.NET Apps
- Always use HTTPS
- Use strong hashing for passwords (via ASP.NET Identity)
- Use token expiration and refresh tokens
- Store secrets securely (e.g., Azure Key Vault, Secret Manager)
- Use middleware for global authentication and authorization
Q: What is the default authentication method in ASP.NET Core?
A: ASP.NET Core uses cookie-based authentication by default in MVC and JWT bearer authentication in Web APIs.
Q: Can I use both cookie and JWT authentication in one project?
A: Yes, using multiple authentication schemes is supported via policy-based setup.
ASP.NET Web API interview questions
RESTful API interview questions
Top Web API interview questions
HTTP methods interview questions
Web API authentication and authorization
Role-based authentication ASP.NET
JWT authentication ASP.NET Core
Difference between authentication and authorization in ASP.NET
How to implement authentication in ASP.NET Core
Policy-based authorization ASP.NET Core
Custom authentication handler ASP.NET
Secure ASP.NET Web API with JWT
ASP.NET Core identity roles and claims
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