C# 更改 ASP.NET Web API 媒体类型格式化程序上的响应标头

Change Response Headers on Media Type Formatter for ASP.NET Web API

提问by Allison A

I have created an ASP.NET web API controller that is returning a strongly typed object on an action, as follows:

我创建了一个 ASP.NET Web API 控制器，它在操作上返回一个强类型对象，如下所示：

// GET api/iosdevices/5
public iOSDevice Get(string id) {
  return new iOSDevice();
}

I have created a BufferedMediaTypeFormatter to handle the type iOSDevice:

我创建了一个 BufferedMediaTypeFormatter 来处理类型 iOSDevice：

public class iOSDeviceXmlFormatter : BufferedMediaTypeFormatter
{
    public iOSDeviceXmlFormatter() {
        SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/xml"));
        SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/xml"));
        SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
    }

    public override void WriteToStream(Type type, object value, Stream writeStream, HttpContent content) {
        content.Headers.ContentType = new MediaTypeHeaderValue("application/xml");
        iOSDevice device = (iOSDevice)value;
        using (XmlWriter writer = XmlWriter.Create(writeStream)) {
            writer.WriteStartElement("iOSDevice");
            if (device.identifierForVendor != Guid.Empty) {
                writer.WriteElementString("identifierForVendor", device.identifierForVendor.ToString());
                writer.WriteElementString("userInterfaceIdiom", device.userInterfaceIdiom);
                writer.WriteElementString("systemName", device.systemName);
                writer.WriteElementString("systemVersion", device.systemVersion);
                writer.WriteElementString("model", device.model);
            }
            writer.WriteEndElement();
        }
        writeStream.Close();
    }
}

My problem is when I catch type "text/html" (e.g. someone attempts to access the API from his or her web browser), the response type is "text/html" instead of "application/xml". I want to override the response type so that the user gets a response that is "application/xml" instead of "text/html".

我的问题是当我捕获类型“text/html”（例如有人试图从他或她的 Web 浏览器访问 API）时，响应类型是“text/html”而不是“application/xml”。我想覆盖响应类型，以便用户获得“application/xml”而不是“text/html”的响应。

I cannot in the ApiController type get access to the "Response" property that is on regular MVC controllers and I am at a loss. How do I override the response type for this action that is being handled by a media type formatter?

我无法在 ApiController 类型中访问常规 MVC 控制器上的“响应”属性，我不知所措。如何覆盖由媒体类型格式化程序处理的此操作的响应类型？

EDIT: HELPFUL NOTE

编辑：有用的注释

I was trying this previously:

我以前试过这个：

var response = Request.CreateResponse<iOSDevice>(HttpStatusCode.Accepted, device);
response.Headers.Remove("Content-Type");
response.Headers.Add("Content-Type", "application/xml; charset=utf-8");
return response;

And it claimed I was "misusing" the headers.

它声称我“滥用”了标题。

But when I used Filip's example below of setting Content directly, it worked!

但是当我使用下面直接设置内容的 Filip 示例时，它起作用了！

var response = Request.CreateResponse();
response.Content = new ObjectContent<iOSDevice>(device, new iOSDeviceXmlFormatter());
return response;

采纳答案by Filip W

When you write to stream in the formatter, headers have been already sent.

当您在格式化程序中写入流时，已发送标头。

You can do this:

你可以这样做：

    public HttpResponseMessage Get(string id) {
    {
        var value = new iOSDevice();
        var response = Request.CreateResponse();
        response.Content = new ObjectContent(typeof(iOSDevice), value, new iOSDeviceXmlFormatter());
        //set headers on the "response"
        return response;
    }

or you can do this (add this method to your formatter):

或者你可以这样做（将此方法添加到格式化程序中）：

    public override void SetDefaultContentHeaders(Type type, HttpContentHeaders headers, string mediaType)
    {
        base.SetDefaultContentHeaders(type, headers, mediaType);
        headers.ContentType = new MediaTypeHeaderValue("application/xml");
    }

Here is an example on how I used the SetDefaultContentHeaderswith a custom formatter: http://www.strathweb.com/2012/09/generate-kindle-mobi-ebooks-with-your-asp-net-web-api/

这是我如何使用SetDefaultContentHeaders自定义格式化程序的示例：http: //www.strathweb.com/2012/09/generate-kindle-mobi-ebooks-with-your-asp-net-web-api/

   public override void SetDefaultContentHeaders(Type type, HttpContentHeaders headers, MediaTypeHeaderValue mediaType)
   {
      if (CanWriteType(type) && mediaType.MediaType == supportedMediaType)
      {
         headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
         headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
         headers.ContentDisposition.FileName = "ebook.mobi";
      }
      else
      {
         base.SetDefaultContentHeaders(type, headers, mediaType);
      }
   }