How to POST Data to an API using C#

A guide on how to send data to an API using the POST method in C# with the HttpClient class, enabling you to easily interact with APIs.

In this article, we will learn how to send data to an API using the POST method in C#. This method is commonly used to create new data on the server.

using System;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json;

class Program
{
    static async Task Main(string[] args)
    {
        var url = "https://example.com/api/data"; // API endpoint
        var data = new
        {
            Name = "Nguyen Van A",
            Age = 23,
            City = "Hanoi"
        };

        using (var client = new HttpClient())
        {
            var json = JsonConvert.SerializeObject(data);
            var content = new StringContent(json, Encoding.UTF8, "application/json");

            var response = await client.PostAsync(url, content);

            if (response.IsSuccessStatusCode)
            {
                Console.WriteLine("Data has been sent successfully!");
            }
            else
            {
                Console.WriteLine("An error occurred: " + response.StatusCode);
            }
        }
    }
}

Detailed Explanation

1. using System;: Imports the basic namespace.
2. using System.Net.Http;: Imports the namespace to use HttpClient.
3. using System.Text;: Imports the namespace to use Encoding.
4. using System.Threading.Tasks;: Imports the namespace for asynchronous programming.
5. using Newtonsoft.Json;: Imports the namespace to use JsonConvert from the Newtonsoft.Json library.
6. var url = "https://example.com/api/data";: The API endpoint where you want to send data.
7. var data = new {...};: Creates an object containing the data to send.
8. using (var client = new HttpClient()): Initializes an instance of HttpClient to send the request.
9. var json = JsonConvert.SerializeObject(data);: Converts the data object to a JSON string.
10. var content = new StringContent(json, Encoding.UTF8, "application/json");: Creates the content for the request with a content type of application/json.
11. var response = await client.PostAsync(url, content);: Sends the POST request to the API and awaits the response.
12. if (response.IsSuccessStatusCode): Checks if the request was successful.
13. Console.WriteLine("Data has been sent successfully!");: Prints a success message.
14. else { ... }: Handles the case where an error occurred.

System Requirements

• .NET Core 3.1 or later or .NET Framework 4.5 or later
• Library: Newtonsoft.Json

How to install the libraries needed to run the C# code above

Use NuGet to install the Newtonsoft.Json library:

Install-Package Newtonsoft.Json

Tips

• Verify the API endpoint and data format before sending.
• Use try-catch to handle errors and exceptions when sending requests.