How can I add Content-Type to header of http post method?

Question

Now I need to connect to a third-party API.

The API needs to set Content-Type to application/json;charset=UTF-8.

I achieve it like this:

var request = new HttpRequestMessage(HttpMethod.Post, "https://api.aaa.com");                        
            request.Content = new StringContent(IP);
            request.Headers.Add("Content-Type", "application/json;charset=UTF-8");            
            var client = clientFactory.CreateClient();
            client.Timeout = TimeSpan.FromSeconds(5);
            var response = await client.SendAsync(request);
            string Content = "";
            if (response.IsSuccessStatusCode)
            {
                Content = await response.Content.ReadAsStringAsync();
                return Content;
            }
            else
            {
                return "";
            }

However, it throws an error:

{"Misused header name, 'Content-Type'. Make sure request headers are used with HttpRequestMessage, response headers with HttpResponseMessage, and content headers with HttpContent objects."}

Soon I found a solution by modifying my code like this:

var request = new HttpRequestMessage(HttpMethod.Post, "https://api.aaa.com");
        var RequestContent = new StringContent(IP);
        RequestContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json;charset=UTF-8");
        request.Content = RequestContent;
        var client = clientFactory.CreateClient();
        client.Timeout = TimeSpan.FromSeconds(5);
        var response = await client.SendAsync(request);
        string Content = "";
        if (response.IsSuccessStatusCode)
        {
            Content = await response.Content.ReadAsStringAsync();
            return Content;
        }
        else
        {
            return "";
        }

Whereas, now it reports another error:

{"The format of value 'application/json;charset=\"UTF-8\"' is invalid."}

What's the matter? And how can I solve this?

Thank you.

Answer 1

You could refer the following sample to set the Content-Type:

HttpClient client = new HttpClient();
client.BaseAddress = new Uri("https://localhost:44310/api/todo/"); //Change the Uri and request content to yours.
client.DefaultRequestHeaders
        .Accept
        .Add(new MediaTypeWithQualityHeaderValue("application/json"));//ACCEPT header

HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, "relativeAddress");
request.Content = new StringContent("{\"name\":\"John Doe\",\"age\":33}",
                                    Encoding.UTF8,
                                    "application/json");//CONTENT-TYPE header

    await client.SendAsync(request)
            .ContinueWith(async responseTask =>
            {
                Console.WriteLine("Response: {0}", responseTask.Result);
                var Content = await responseTask.Result.Content.ReadAsStringAsync();
            });

And the web API method like this:

[HttpPost]
[Route("relativeAddress")]
public string GetAddress([FromBody]TestUserViewModel testUser)
{
    return "Address A";
}

View Model:

public class TestUserViewModel
{
    public string Name { get; set; }
    public int Age { get; set; }
}

The result as below: