.net core 2.2返回304状态码。这是使用ApiController。

    [HttpGet]
    public ActionResult<YOUROBJECT> Get()
    {
        return StatusCode(304);
    }

您还可以选择返回带有响应的对象

    [HttpGet]
    public ActionResult<YOUROBJECT> Get()
    {
        return StatusCode(304, YOUROBJECT); 
    }

我不知道答案所以问ASP。NET团队。

因此，诀窍是将签名更改为HttpResponseMessage并使用Request.CreateResponse。

[ResponseType(typeof(User))]
public HttpResponseMessage GetUser(HttpRequestMessage request, int userId, DateTime lastModifiedAtClient)
{
    var user = new DataEntities().Users.First(p => p.Id == userId);
    if (user.LastModified <= lastModifiedAtClient)
    {
         return new HttpResponseMessage(HttpStatusCode.NotModified);
    }
    return request.CreateResponse(HttpStatusCode.OK, user);
}

如果您希望将操作签名保留为返回User，还可以执行以下操作:

public User GetUser(int userId, DateTime lastModifiedAtClient) 

如果你想返回200以外的值，那么你在你的动作中抛出一个HttpResponseException，并传递你想要发送给客户端的HttpResponseMessage。

我讨厌撞旧文章，但这是在谷歌搜索的第一个结果，我有一个问题(即使有你们的支持)。所以这里什么都没有……

希望我的解决方案能帮助那些同样感到困惑的人。

namespace MyApplication.WebAPI.Controllers
{
    public class BaseController : ApiController
    {
        public T SendResponse<T>(T response, HttpStatusCode statusCode = HttpStatusCode.OK)
        {
            if (statusCode != HttpStatusCode.OK)
            {
                // leave it up to microsoft to make this way more complicated than it needs to be
                // seriously i used to be able to just set the status and leave it at that but nooo... now 
                // i need to throw an exception 
                var badResponse =
                    new HttpResponseMessage(statusCode)
                    {
                        Content =  new StringContent(JsonConvert.SerializeObject(response), Encoding.UTF8, "application/json")
                    };

                throw new HttpResponseException(badResponse);
            }
            return response;
        }
    }
}

然后从BaseController继承

[RoutePrefix("api/devicemanagement")]
public class DeviceManagementController : BaseController
{...

然后使用它

[HttpGet]
[Route("device/search/{property}/{value}")]
public SearchForDeviceResponse SearchForDevice(string property, string value)
{
    //todo: limit search property here?
    var response = new SearchForDeviceResponse();

    var results = _deviceManagementBusiness.SearchForDevices(property, value);

    response.Success = true;
    response.Data = results;

    var statusCode = results == null || !results.Any() ? HttpStatusCode.NoContent : HttpStatusCode.OK;

    return SendResponse(response, statusCode);
}

.net core 2.2返回304状态码。这是使用ApiController。

    [HttpGet]
    public ActionResult<YOUROBJECT> Get()
    {
        return StatusCode(304);
    }

您还可以选择返回带有响应的对象

    [HttpGet]
    public ActionResult<YOUROBJECT> Get()
    {
        return StatusCode(304, YOUROBJECT); 
    }

另一个选择:

return new NotModified();

public class NotModified : IHttpActionResult
{
    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = new HttpResponseMessage(HttpStatusCode.NotModified);
        return Task.FromResult(response);
    }
}