httpclient call to webapi to post data not working

Question

I need to make a simple webapi call to post method with string argument.

Below is the code I'm trying, but when the breakpoint is hit on the webapi method, the received value is null.

StringContent stringContent = new System.Net.Http.StringContent("{ \"firstName\": \"John\" }", System.Text.Encoding.UTF8, "application/json");
HttpClient client = new HttpClient();
HttpResponseMessage response = await client.PostAsync(url.ToString(), stringContent);

and server side code:

 // POST api/values
[HttpPost]
public void Post([FromBody]string value)
{
}

please help...

Answer 1

If you want to send a json to your Web API, the best option is to use a model binding feature, and use a Class, instead a string.

Create a model

public class MyModel
{
    [JsonProperty("firstName")]
    public string FirstName { get; set; }
}

If you wont use the JsonProperty attribute, you can write property in lower case camel, like this

public class MyModel
{
    public string firstName { get; set; }
}

Then change you action, change de parameter type to MyModel

[HttpPost]
public void Post([FromBody]MyModel value)
{
    //value.FirstName
}

You can create C# classes automatically using Visual Studio, look this answer here Deserialize JSON into Object C#

I made this following test code

Web API Controller and View Model

using System.Web.Http;
using Newtonsoft.Json;

namespace WebApplication3.Controllers
{
    public class ValuesController : ApiController
    {
        [HttpPost]
        public string Post([FromBody]MyModel value)
        {
            return value.FirstName.ToUpper();
        }
    }

    public class MyModel
    {
        [JsonProperty("firstName")]
        public string FirstName { get; set; }
    }
}

Console client application

using System;
using System.Net.Http;

namespace Temp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Enter to continue");
            Console.ReadLine();
            DoIt();
            Console.ReadLine();
        }

        private static async void DoIt()
        {
            using (var stringContent = new StringContent("{ \"firstName\": \"John\" }", System.Text.Encoding.UTF8, "application/json"))
            using (var client = new HttpClient())
            {
                try
                {
                    var response = await client.PostAsync("http://localhost:52042/api/values", stringContent);
                    var result = await response.Content.ReadAsStringAsync();
                    Console.WriteLine(result);
                }
                catch (Exception ex)
                {
                    Console.ForegroundColor = ConsoleColor.Red;
                    Console.WriteLine(ex.Message);
                    Console.ResetColor();
                }
            }
        }
    }
}

Output

Enter to continue

"JOHN"

Answer 2

Alternative answer: You can leave your input parameter as string

[HttpPost]
public void Post([FromBody]string value)
{
}

, and call it with the C# httpClient as follows:

var kvpList = new List<KeyValuePair<string, string>>
{
    new KeyValuePair<string, string>("", "yo! r u dtf?")
};
FormUrlEncodedContent rqstBody = new FormUrlEncodedContent(kvpList);


string baseUrl = "http://localhost:60123"; //or "http://SERVERNAME/AppName"
string C_URL_API = baseUrl + "/api/values";
using (var httpClient = new HttpClient())
{
    try
    {   
        HttpResponseMessage resp = await httpClient.PostAsync(C_URL_API, rqstBody); //rqstBody is HttpContent
        if (resp != null && resp.Content != null) {
            var result = await resp.Content.ReadAsStringAsync();
            //do whatevs with result
        } else
            //nothing returned.
    }
    catch (Exception ex)
    {
        Console.ForegroundColor = ConsoleColor.Red;
        Console.WriteLine(ex.Message);
        Console.ResetColor();
    }
}