c#之无法在 WebApi 响应中设置 Content-MD5 header

当我尝试设置 Content-MD5 -标题我得到这个异常

System.InvalidOperationException wurde nicht von Benutzercode behandelt. 
  HResult=-2146233079 
  Message=Misused header name. Make sure request headers are used with HttpRequestMessage, response headers with HttpResponseMessage, and content headers with HttpContent objects. 
  Source=System.Net.Http 
  StackTrace: 
       bei System.Net.Http.Headers.HttpHeaders.CheckHeaderName(String name) 
       bei System.Net.Http.Headers.HttpHeaders.Add(String name, String value) 
       bei caching_test.Controllers.ValuesController.Get(Int32 id) in C:\Users\ulbricht\Documents\Bitbucket\caching-system\caching test\Controllers\ValuesController.cs:Zeile 35. 
       bei lambda_method(Closure , Object , Object[] ) 
       bei System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass13.<GetExecutor>b__c(Object instance, Object[] methodParameters) 
       bei System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments) 
       bei System.Web.Http.Controllers.ReflectedHttpActionDescriptor.<>c__DisplayClass5.<ExecuteAsync>b__4() 
       bei System.Threading.Tasks.TaskHelpers.RunSynchronously[TResult](Func`1 func, CancellationToken cancellationToken) 
  InnerException:  

public HttpResponseMessage Get(int id) 
{ 
    var result = "value" + id; 
    var hash = Convert.ToBase64String(MD5.Create().ComputeHash(UTF8Encoding.UTF8.GetBytes(result))); 
    if (Request.Headers.FirstOrDefault(h => h.Key == "Content-MD5").Value != null) 
    { 
        var hashvalue = Request.Headers.FirstOrDefault(h => h.Key == "Content-MD5").Value.FirstOrDefault(); 
        if (hashvalue == hash) 
        { 
            return Request.CreateResponse(HttpStatusCode.NotModified); 
        } 
    } 
    var response = Request.CreateResponse(HttpStatusCode.OK, result); 
    response.Headers.Add("Content-MD5", hash); // <------- Here comes the error 
    return response; 
} 

请您参考如下方法:

或者，您甚至可以使用为此目的明确设计的 header 属性。不需要魔术字符串。

response.Content.Headers.ContentMD5 = MD5.Create().ComputeHash(UTF8Encoding.UTF8.GetBytes(result));