IActionResult vs IResult ASP.NET Core

Question

What is the difference between Microsoft.AspNetCore.Http.IResult and Microsoft.AspNetCore.Mvc.IActionResult? Which one should I use when I'm going to build an API? I usually use the Results class with its methods for that.

Answer 1

IActionResult vs IResult

IActionResult

IActionResult is part of the MVC framework. It is found in Microsoft.AspNetCore.Mvc namespace in the Microsoft.AspNetCore.Mvc.Abstractions.dll library. Commonly it is used in MVC-based web API implementations. This has existed for quite some time, since around when ASP.NET MVC was first started. It exists in the .NET Framework, and all versions of .NET Core / .NET.

Microsoft Learn: IActionResult Interface

IResult

IResult is part of the new API framework introduced as part of .NET 6.0. It is found in the Microsoft.AspNetCore.Http namespace in the Microsoft.AspNetCore.Http.Abstractions.dll library. IResult is fully supported with the new minimal APIs features of .NET 6.0+.

Microsoft Learn: IResult Interface

Do they inherit from each other?

No, these interfaces are completely separate, coming from separate namespaces and libraries.

When should I use one vs the other?

This depends, but generally, if you are working with an MVC-based API controller, you should consider using IActionResult (or the base ActionResult class, if desired).

If you are writing APIs without MVC using .NET 6.0+, either using the Minimal API framework or something else, you should consider using IResult.

Consider using the framework-provided IResult-derived classes (TypedResults or Results) instead of the IResult interface directly 1.

Additional Microsoft Learn Resources

Here are some excellent resources from Microsoft Learn that provide overviews and helpful insights into each of these areas of API development.

Microsoft Learn: Controller action return types in ASP.NET Core web API

Microsoft Learn: ASP.NET Core Fundamentals Overview

Microsoft Learn: Tutorial: Create a minimal API with ASP.NET Core

Microsoft Learn: Tutorial: Create a web API with ASP.NET Core

Microsoft Learn: Overview of ASP.NET Core MVC

Answer 2

IActionResult defines sort of contract, as it is an interface, which allows you to provide some more operations based on your actions like redirecting, changing the response's format etc.. Actions are like new layer in the code between http dialogues and your MVC web application to provide more operations depends on http requests so you will be able to reach any of endpoints in your API by any type of request that correspond with Http protocol. I highly recommend you to use IActionResult on the side of your web application - MVC, since it gives you more approaches to handle requests. Hope it helped you :)