How to Send x-www-form-urlencoded Data with HttpClient in C#

For example, c# post x-www-form-urlencoded using HttpClient

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

public class ApiClient
{
    private static HttpClient _httpClient = new HttpClient();

    public async Task<string> PostLoginFormData()
    {
        // Prepare form data
        var data = new[]
        {
            new KeyValuePair<string, string>("username", "user123"),
            new KeyValuePair<string, string>("password", "password123"),
            new KeyValuePair<string, string>("rememberMe", "true")
        };

        // Set up the content with x-www-form-urlencoded
        var content = new FormUrlEncodedContent(data);

        // Send the POST request to the server (replace with your API URL)
        var response = await _httpClient.PostAsync("https://example.com/login", content);

        // Check for errors in the response
        if (!response.IsSuccessStatusCode)
        {
            throw new Exception($"{response.StatusCode}: {response.ReasonPhrase}");
        }

        // Read and return the response content (assumed to be JSON)
        var responseJson = await response.Content.ReadAsStringAsync();
        return responseJson;
    }
}

In this example:

• Form Data: A KeyValuePair<string, string> array holds the form fields ("username", "password", "rememberMe").
• FormUrlEncodedContent: This is automatically encoded to application/x-www-form-urlencoded.
• PostAsync: Sends a POST request with the form data as the content.
• Error Handling: If the response is unsuccessful, it throws an exception with the status code and reason phrase.
• Response: Reads the response body (assumed to be JSON in this case)

The FormUrlEncodedContent automatically assigns the Content-Type header to application/x-www-form-urlencoded.

Using IHttpClientFactory ensures that HttpClient instances are reused and not created for each request, which is a best practice for managing HTTP connections.