Sending a List of objects through PostAsync

Question

I have a list of objects each one made like this :

public class PostElement {
public string field1 {get;set;}
public string field2 {get:set:}
public string field3 {get;set;}
}

I need to send this list :

List<PostElement> ElementList  = new List<PostElement>();

using a :

HttpClient.PostAsync (url , content); 

How should I create the content using the List above ?

I tried everything I could think of : serializing every element of the list to a JsonContent, and then inserting each of these JsonContent elements into a MultiPartContent ; serializing the whole list to a StringContent, serializing the whole list to a JsonContent.

None of these methods worked so far .

Is there any chance I could send this List using a PostAsync, or should I give up the idea ?

Answer 1

We need basic information. Are you targeting .NET Framework ASP.NET Core? What is the client; Web Forms, MVC, Web API? What's the server; Web Forms, MVC, Web API? Can you at least provide the code you've tried both server and client?

Is there any chance I could send this List using a PostAsync, or should I give up the idea ?

Of course, the official documentation covers how to post a complex type.

https://learn.microsoft.com/en-us/dotnet/fundamentals/networking/http/httpclient

Answer 2

Do you want to serialize List<PostElement> object to JSON string and send it to web server using HttpClient?

Yes Exaclty .I need to serialize the plain List into a Json string and send it by using a PostAsync

Please see the following sample code:

using System.Collections.Generic;
using System.IO;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleAppSystemTextJson
{
    internal class Program
    {
        static async Task Main(string[] args)
        {
            // Create List<PostElement> object
            // for example:
            var elements = new List<PostElement>
            {
                new PostElement { field1 = "a", field2 = "b", field3 = "c" },
                new PostElement { field1 = "d", field2 = "e", field3 = "f" },
                new PostElement { field1 = "g", field2 = "h", field3 = "i" }
            };

            // Serialize List<PostElement> object to JSON string
            var jsonString = System.Text.Json.JsonSerializer.Serialize(elements);

            // url to send JSON string
            var url = "https://example.com/api";

            // Create HttpRequestMessage
            var request = new HttpRequestMessage(HttpMethod.Post, url);
            request.Content = new StringContent(jsonString,
                                                Encoding.UTF8,
                                                "application/json");

            // Create HttpClient
            var client = new HttpClient();

            // Post the JSON string to the url
            var response = await client.SendAsync(request);

            // if you need to do something with response data
            using (Stream responseStream = await response.Content.ReadAsStreamAsync())
            {
                // Proccess response data as required
            }
        }
    }

    public class PostElement
    {
        public string field1 { get; set; }
        public string field2 { get; set; }
        public string field3 { get; set; }
    }
}