How do I set multiple headers using PostAsync in C#?

Question

I have some working code:

using (var client = new HttpClient())
{
HttpResponseMessage response;
response = client.PostAsync(Url, new StringContent(Request, Encoding.UTF8, header)).Result;
}

// the above works fine for a simple header, e.g. "application/json"

What do I do, if I want to have multiple headers? E.g. adding "myKey", "foo" pair and "Accept", "image/foo1"

If I try adding the following before the .Result line, intellisense complains (the word 'Headers' is in red with "Can't resolve symbol 'Headers'":

client.Headers.Add("myKey", "foo");
client.Headers.Add("Accept", "image/foo1");

Answer 1

You can access the Headers property through the StringContent:

var content = new StringContent(Request, Encoding.UTF8, header);
content.Headers.Add(...);

Then pass the StringContent to the PostAsync call:

response = client.PostAsync(Url, content).Result;

Answer 2

I stopped using the Post/Get *Async methods in favor of the SendAsync(...) method and HttpRequestMessage Send Async is the big brother which allows you the full flexibility you otherwise can't achieve.

using System.Net.Http;

var httpRequestMessage = new HttpRequestMessage();

httpRequestMessage.Method = httpMethod;
httpRequestMessage.RequestUri = new Uri(url);

httpRequestMessage.Headers
                  .UserAgent
                  .Add(new Headers.ProductInfoHeaderValue(
                                              _applicationAssembly.Name, 
                                              _applicationAssembly.Version.ToString()));

HttpContent httpContent = new StringContent(json, Encoding.UTF8, "application/json");
switch (httpMethod.Method)
{
    case "POST":
        httpRequestMessage.Content = httpContent;
        break;
}

var result = await httpClient.SendAsync(httpRequestMessage);
result.EnsureSuccessStatusCode();

Answer 3

You can also use

var client = new HttpClient();
client.DefaultRequestHeaders.TryAddWithoutValidation("headername","headervalue");

If you want to just set the headers on the HttpClient class just once. Here is the MSDN docs on DefaultRequestHeaders.TryAddWithoutValidation