C# 如何填充HttpWebRequest头？

我正在尝试填充以下代码：

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = "GET";
request.Headers.Add("Authorization", "Bearer " + authToken.token.access_token);
request.Accept = "application/json";

但是运行单元测试会在这一部分引发一个异常：request.Headers.Add，因为request.Headers为null。尽管在我的测试中初始化了头文件，但是：

ShimHttpWebRequest request = new ShimHttpWebRequest();
ShimWebRequest.CreateString = (urio) => {
   request.Instance.Headers = new WebHeaderCollection {
        {"Authorization", "Bearer abcd1234"}
   };
   //also tried initilizing it like this:
   //WebHeaderCollection headers = new WebHeaderCollection();
   //headers[HttpRequestHeader.Authorization] = "Bearer abcd1234";
   //request.Instance.Headers = headers;
   return request.Instance;
};

但是request.Instance.Headers仍然为null

---

我缺少什么？

这是我的代码，您可以试试：

public static string HttpPostWebRequest(string requestUrl, int timeout, string requestXML, bool isPost, string encoding, out string msg)
    {

        msg = string.Empty;
        string result = string.Empty;

        try
        {

            byte[] bytes = System.Text.Encoding.GetEncoding(encoding).GetBytes(requestXML);
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(requestUrl);
            request.ContentType = "application/x-www-form-urlencoded";
            request.Referer = requestUrl;
            request.Method = isPost ? "POST" : "GET";
            request.ContentLength = bytes.Length;
            request.Timeout = timeout * 1000;

            using (Stream requestStream = request.GetRequestStream())
            {
                requestStream.Write(bytes, 0, bytes.Length);
                requestStream.Close();
            }

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream responseStream = response.GetResponseStream();

            if (responseStream != null)
            {
                StreamReader reader = new StreamReader(responseStream, System.Text.Encoding.GetEncoding(encoding));
                result = reader.ReadToEnd();
                reader.Close();
                responseStream.Close();
                request.Abort();
                response.Close();
                return result.Trim();
            }

        }
        catch (Exception ex)
        {
            msg = ex.Message + ex.StackTrace;
        }

        return result;

    }

---

我通过为标题创建一个getter来解决这个问题，这样它将返回WebHeaderCollection而不是null

---

我通过如下实例化ShimHttpWebRequest的Header属性解决了这个问题

var httpWebRequest = new ShimHttpWebRequest() { HeadersGet = () => new WebHeaderCollection() };
ShimWebRequest.CreateString = (arg1) => httpWebRequest.Instance;

var httpWebRequest = new ShimHttpWebRequest() { HeadersGet = () => new WebHeaderCollection() };
ShimWebRequest.CreateString = (arg1) => httpWebRequest.Instance;