ASP.NET Interview Questions（2025）

Question: What is the IActionResult interface in ASP.NET MVC?

Answer:

**IActionResult** is an interface in ASP.NET MVC (and also in ASP.NET Core MVC) that represents the result of an action method. In MVC (Model-View-Controller) applications, an action method in a controller returns an instance of IActionResult, which is used to define the response that will be sent back to the client (typically a web browser).

The primary purpose of IActionResult is to abstract the different types of possible responses that an action method might return. This allows for greater flexibility, as various results such as views, redirects, JSON data, files, status codes, etc., can be returned using different implementations of IActionResult.

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Key Characteristics of IActionResult:

1. Abstraction of Result Types: IActionResult is a generic interface that allows different types of results to be returned from an action. These results can include views, redirects, file downloads, error responses, and more.

2. Action Method Return Type: In an MVC controller, the action methods typically return an IActionResult. The specific result returned depends on what the controller needs to do, such as returning a view, redirecting to another action, returning JSON, or handling file downloads.

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Common Implementations of IActionResult:

ASP.NET MVC provides several built-in classes that implement IActionResult. Here are the most commonly used ones:

1. ViewResult: Represents a View (HTML content) to be rendered by the client (browser). It’s used when you want to return a page with HTML markup.

   Example:

   public IActionResult Index()
   {
       return View(); // Returns a view to the client
   }

2. RedirectToActionResult: Represents a redirect to another action within the same or different controller. It is commonly used for redirecting users after performing a POST operation (to avoid duplicate submissions).

   Example:

   public IActionResult RedirectToHome()
   {
       return RedirectToAction("Index", "Home"); // Redirects to the Index action of the Home controller
   }

3. JsonResult: Represents JSON data that is returned to the client. It is used when returning data in JSON format (e.g., for AJAX requests or APIs).

   Example:

   public IActionResult GetData()
   {
       var data = new { Name = "John", Age = 30 };
       return Json(data); // Returns JSON data to the client
   }

4. ContentResult: Represents plain text content that is returned to the client. This can be used for returning simple strings or text content.

   Example:

   public IActionResult GetText()
   {
       return Content("Hello, World!"); // Returns plain text content
   }

5. FileResult: Represents a file download or a file response. This is commonly used for returning files (e.g., PDFs, images, or any file type) to the client.

   Example:

   public IActionResult DownloadFile()
   {
       var filePath = "path/to/file.pdf";
       return File(filePath, "application/pdf", "example.pdf"); // Returns a file to the client
   }

6. StatusCodeResult: Represents a specific HTTP status code to be returned to the client, often used for API responses where you need to specify status codes such as 200 OK, 404 Not Found, or 500 Internal Server Error.

   Example:

   public IActionResult NotFoundExample()
   {
       return NotFound(); // Returns a 404 HTTP status code
   }

7. BadRequestResult: Represents a 400 Bad Request status code, typically used when there is an issue with the client’s request.

   Example:

   public IActionResult BadRequestExample()
   {
       return BadRequest("Invalid request data."); // Returns a 400 Bad Request with a message
   }

8. OkObjectResult: Represents a 200 OK status code with an object. This is commonly used in API responses where data is returned with a successful status.

   Example:

   public IActionResult GetApiData()
   {
       var data = new { Message = "Success" };
       return Ok(data); // Returns a 200 OK response with data in JSON format
   }

9. EmptyResult: Represents a no content response. This is used when you want to return a 204 No Content response, such as after successfully processing a request but not needing to return any data.

   Example:

   public IActionResult DeleteRecord(int id)
   {
       // Perform delete logic here
       return new EmptyResult(); // Returns a 204 No Content response
   }

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Why Use IActionResult?

1. Flexibility: The IActionResult interface allows action methods to return various types of responses, making it flexible for different use cases such as views, redirects, API responses, and error handling.

2. Consistency: All action methods return types that implement IActionResult, maintaining consistency across the application and simplifying code management.

3. Extensibility: Developers can implement custom IActionResult types if needed, providing flexibility for custom action results that go beyond the built-in ones.

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Example of IActionResult in Action:

Here’s an example of a controller with different IActionResult implementations:

public class HomeController : Controller
{
    // Returns a view to the user
    public IActionResult Index()
    {
        return View();
    }

    // Redirects to another action
    public IActionResult RedirectToHome()
    {
        return RedirectToAction("Index", "Home");
    }

    // Returns JSON data
    public IActionResult GetData()
    {
        var data = new { Name = "John", Age = 30 };
        return Json(data);
    }

    // Returns a file for download
    public IActionResult DownloadFile()
    {
        var filePath = "path/to/file.pdf";
        return File(filePath, "application/pdf", "example.pdf");
    }

    // Returns a 404 error
    public IActionResult NotFoundExample()
    {
        return NotFound();
    }
}

In this example:

• The Index() method returns a view.
• The RedirectToHome() method returns a redirect to another action.
• The GetData() method returns JSON data.
• The DownloadFile() method returns a file download.
• The NotFoundExample() method returns a 404 Not Found error.

Each method is returning an object that implements IActionResult, allowing the controller to return different types of responses based on the requirements.

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Conclusion:

In ASP.NET MVC, the IActionResult interface is a central concept that allows action methods in controllers to return different types of responses. By abstracting various types of results such as views, redirects, JSON, files, and HTTP status codes, IActionResult provides a flexible and extensible mechanism for handling responses in MVC applications. This abstraction makes the controller code cleaner, more modular, and easier to maintain.

Question: What is the difference between Server.Transfer and Response.Redirect in ASP.NET?

Answer:

In ASP.NET, Server.Transfer and Response.Redirect are both used to navigate between pages, but they differ in how the request is handled, the behavior of the application, and the user experience. Here’s a detailed explanation of both methods and their differences:

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1. Server.Transfer:

Server.Transfer transfers the current request to a different page on the server without the client’s knowledge. The server processes the request for the new page, but it does not send a response to the browser with a new URL.

Characteristics:

• Server-side transfer: The transfer is handled entirely on the server. The URL in the browser remains the same (it does not change).
• No round trip: Since the transfer is handled on the server, it doesn’t require a round trip to the client. The server simply processes the new page and sends the result back to the client.
• Faster: Because there is no need to round-trip the request to the client and then back to the server, it can be faster, especially in scenarios where page transitions happen on the same server.
• No new HTTP request: The HTTP request and response headers are not re-sent. The existing request is used to process the new page.
• Preserves server-side state: The current server-side state (like session data) is preserved because the same request is used.

Example:

Server.Transfer("NewPage.aspx");

• This will cause the request to be processed by NewPage.aspx, but the URL in the browser will not change (it will still display the URL of the page that initiated the transfer).

Use Cases:

• Internal redirects within the same application or website.
• Page transitions where you don’t want the URL to change or when the client doesn’t need to know that the page has changed (useful in certain internal processes).
• Performance optimization in situations where you don’t want the browser to initiate a new HTTP request.

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2. Response.Redirect:

Response.Redirect is used to send a new HTTP request to the client, which causes the browser to navigate to a new URL. This is a client-side redirect, meaning that the browser is instructed to load a new page.

Characteristics:

• Client-side redirect: The redirect happens on the client side. The URL in the browser changes to the new page’s URL.
• Round trip: When using Response.Redirect, the server sends an HTTP response to the browser, which then makes a new request to the server for the new page.
• Slower: This method involves a round trip to the client and back to the server, so it can be slower compared to Server.Transfer.
• New HTTP request: A new HTTP request is initiated, and the server processes the new request for the target page. All headers and states are reset.
• URL changes: The URL in the browser changes to the target URL.
• State is lost: Any server-side state (e.g., request parameters, form data) is not automatically carried over. You will need to explicitly pass this data using query strings, session variables, or other mechanisms.

Example:

Response.Redirect("NewPage.aspx");

• This will redirect the user to NewPage.aspx, and the browser URL will change accordingly.

Use Cases:

• External redirects to other websites or different domains.
• When you want the browser’s URL to change, such as when navigating to a different part of your site.
• Redirecting after a form submission or after completing a process, such as a user logging in or submitting data.

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Key Differences:

Feature	Server.Transfer	Response.Redirect
Request Handling	Server-side; does not create a new request.	Client-side; creates a new HTTP request.
URL in Browser	The browser’s URL does not change.	The browser’s URL changes to the target page’s URL.
Performance	Faster (no round trip to the client).	Slower (requires round trip to the client).
State Preservation	Preserves server-side state (like session, request).	State (like form data) is lost unless explicitly passed.
Use Case	Internal page navigation within the same site.	Redirecting to another page, domain, or external resource.
Response Code	No HTTP status code (no response sent to the client).	Sends HTTP status code (302 - Found or 301 - Moved Permanently).
Browser Visibility	Not visible to the user (URL remains the same).	Visible to the user (URL in the browser address bar changes).

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Summary:

• Server.Transfer is used for transferring control to another page on the server without notifying the client, and the browser’s URL does not change. It is typically used for internal navigation and can offer performance benefits.

• Response.Redirect sends a new request to the client, resulting in a client-side redirect with a change in the browser’s URL. It is commonly used when you need the browser to navigate to a different URL or external site.

When to Use:

• Use Server.Transfer when you want to transfer control to another page within the same application without a round trip to the client and without changing the URL.
• Use Response.Redirect when you need the browser to navigate to a new URL and when you want the URL to change in the browser’s address bar. This is often used for external redirects or after completing an action (like form submission).

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