AspNetCore.Docs/aspnet/web-api/overview/getting-started-with-aspnet-web-api/action-results.md

uid	title	author	description	ms.author	manager	ms.date	ms.topic	ms.assetid	ms.technology	ms.prod	msc.legacyurl	msc.type
web-api/overview/getting-started-with-aspnet-web-api/action-results	Action Results in Web API 2 | Microsoft Docs	MikeWasson		aspnetcontent	wpickett	02/03/2014	article	2fc4797c-38ef-4cc7-926c-ca431c4739e8	dotnet-webapi	.net-framework	/web-api/overview/getting-started-with-aspnet-web-api/action-results	authoredcontent

Action Results in Web API 2

by Mike Wasson

This topic describes how ASP.NET Web API converts the return value from a controller action into an HTTP response message.

A Web API controller action can return any of the following:

1. void
2. HttpResponseMessage
3. IHttpActionResult
4. Some other type

Depending on which of these is returned, Web API uses a different mechanism to create the HTTP response.

Return type	How Web API creates the response
void	Return empty 204 (No Content)
HttpResponseMessage	Convert directly to an HTTP response message.
IHttpActionResult	Call ExecuteAsync to create an HttpResponseMessage, then convert to an HTTP response message.
Other type	Write the serialized return value into the response body; return 200 (OK).

The rest of this topic describes each option in more detail.

void

If the return type is void, Web API simply returns an empty HTTP response with status code 204 (No Content).

Example controller:

[!code-csharpMain]

HTTP response:

[!code-consoleMain]

HttpResponseMessage

If the action returns an HttpResponseMessage, Web API converts the return value directly into an HTTP response message, using the properties of the HttpResponseMessage object to populate the response.

This option gives you a lot of control over the response message. For example, the following controller action sets the Cache-Control header.

[!code-csharpMain]

Response:

[!code-consoleMain]

If you pass a domain model to the CreateResponse method, Web API uses a media formatter to write the serialized model into the response body.

[!code-csharpMain]

Web API uses the Accept header in the request to choose the formatter. For more information, see Content Negotiation.

IHttpActionResult

The IHttpActionResult interface was introduced in Web API 2. Essentially, it defines an HttpResponseMessage factory. Here are some advantages of using the IHttpActionResult interface:

• Simplifies unit testing your controllers.
• Moves common logic for creating HTTP responses into separate classes.
• Makes the intent of the controller action clearer, by hiding the low-level details of constructing the response.

IHttpActionResult contains a single method, ExecuteAsync, which asynchronously creates an HttpResponseMessage instance.

[!code-csharpMain]

If a controller action returns an IHttpActionResult, Web API calls the ExecuteAsync method to create an HttpResponseMessage. Then it converts the HttpResponseMessage into an HTTP response message.

Here is a simple implementaton of IHttpActionResult that creates a plain text response:

[!code-csharpMain]

Example controller action:

[!code-csharpMain]

Response:

[!code-consoleMain]

More often, you will use the IHttpActionResult implementations defined in the System.Web.Http.Results namespace. The ApiController class defines helper methods that return these built-in action results.

In the following example, if the request does not match an existing product ID, the controller calls ApiController.NotFound to create a 404 (Not Found) response. Otherwise, the controller calls ApiController.OK, which creates a 200 (OK) response that contains the product.

[!code-csharpMain]

Other Return Types

For all other return types, Web API uses a media formatter to serialize the return value. Web API writes the serialized value into the response body. The response status code is 200 (OK).

[!code-csharpMain]

A disadvantage of this approach is that you cannot directly return an error code, such as 404. However, you can throw an HttpResponseException for error codes. For more information, see Exception Handling in ASP.NET Web API.

Web API uses the Accept header in the request to choose the formatter. For more information, see Content Negotiation.

Example request

[!code-consoleMain]

Example response:

[!code-consoleMain]