.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); 
    }

我不喜欢改变我的签名来使用HttpCreateResponse类型，所以我提出了一个扩展的解决方案来隐藏它。

public class HttpActionResult : IHttpActionResult
{
    public HttpActionResult(HttpRequestMessage request) : this(request, HttpStatusCode.OK)
    {
    }

    public HttpActionResult(HttpRequestMessage request, HttpStatusCode code) : this(request, code, null)
    {
    }

    public HttpActionResult(HttpRequestMessage request, HttpStatusCode code, object result)
    {
        Request = request;
        Code = code;
        Result = result;
    }

    public HttpRequestMessage Request { get; }
    public HttpStatusCode Code { get; }
    public object Result { get; }

    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        return Task.FromResult(Request.CreateResponse(Code, Result));
    }
}

然后你可以添加一个方法到你的ApiController(或者更好的是你的基本控制器)，像这样:

protected IHttpActionResult CustomResult(HttpStatusCode code, object data) 
{
    // Request here is the property on the controller.
    return new HttpActionResult(Request, code, data);
}

然后你可以像任何内置方法一样返回它:

[HttpPost]
public IHttpActionResult Post(Model model)
{
    return model.Id == 1 ?
                Ok() :
                CustomResult(HttpStatusCode.NotAcceptable, new { 
                    data = model, 
                    error = "The ID needs to be 1." 
                });
}

ASP。NET Web Api 2，这篇文章从MS建议改变方法的返回类型IHttpActionResult。然后，您可以返回一个内置的IHttpActionResult实现，如Ok, BadRequest等(参见这里)或返回您自己的实现。

对于你的代码，可以这样做:

public IHttpActionResult GetUser(int userId, DateTime lastModifiedAtClient)
{
    var user = new DataEntities().Users.First(p => p.Id == userId);
    if (user.LastModified <= lastModifiedAtClient)
    {
        return StatusCode(HttpStatusCode.NotModified);
    }
    return Ok(user);
}

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);
}

试试这个:

return new ContentResult() { 
    StatusCode = 404, 
    Content = "Not found" 
};

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。