title: How can I include If-None-Match header in HttpRequestMessage
body: <p>I have a HttpRequestMessage as follows:</p>
  
  <pre><code>string URI = "http://" + MyHostName.DisplayName.ToString() + "/datastore/";
  
  HttpClient client = new HttpClient();
  HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, URI);
  string Params = "";
  request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/plain"));
  request.Headers.AcceptCharset.Add(new StringWithQualityHeaderValue("utf-8", 0.7));
  request.Headers.AcceptLanguage.Add(new StringWithQualityHeaderValue("en-us", 0.5));
  request.Content = new StreamContent(new MemoryStream(System.Text.Encoding.UTF8.GetBytes(Params)));
  request.Content.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
  
  try
  {
      var result = await client.SendAsync(request);
      var content = await result.Content.ReadAsStringAsync();
      return content.ToString();
  }
  catch (HttpRequestException)
  {
      Connected = false;
      return "";
  }
  </code></pre>
  
  <p>I want to add a <code>If-None-Match</code> header to my request with a value like <code>'8001'</code> as an example. But when I lookup <a href="https://msdn.microsoft.com/en-us/library/system.net.http.headers.httprequestheaders.ifnonematch(v=vs.118).aspx" rel="nofollow noreferrer">HttpRequestHeaders.IfNoneMatch</a> you can only get it and not set it.</p>
  
  <p>Any Ideas?</p>
  
  <p>Edit 1: Added that system is running UWP on Windows 10</p>