请用c#编程封装一个http请求的帮助类

在C#中封装一个HTTP请求的帮助类，你可以使用`HttpClient`类，它提供了发送HTTP请求和接收HTTP响应的功能。以下是一个简单的示例：

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

public class HttpHelper
{
    private readonly HttpClient _httpClient;

    public HttpHelper(string baseAddress)
    {
        _httpClient = new HttpClient
        {
            BaseAddress = new Uri(baseAddress)
        };
    }

    // GET请求
    public async Task<string> GetAsync(string requestUri)
    {
        try
        {
            HttpResponseMessage response = await _httpClient.GetAsync(requestUri);
            if (response.IsSuccessStatusCode)
            {
                return await response.Content.ReadAsStringAsync();
            }
            else
            {
                // 处理错误状态码
                throw new HttpRequestException($"Error: {response.ReasonPhrase}");
            }
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine("\nException Caught!");
            Console.WriteLine("Message :{0} ", e.Message);
            return string.Empty;
        }
    }

    // POST请求
    public async Task<string> PostAsync(string requestUri, StringContent content)
    {
        try
        {
            HttpResponseMessage response = await _httpClient.PostAsync(requestUri, content);
            if (response.IsSuccessStatusCode)
            {
                return await response.Content.ReadAsStringAsync();
            }
            else
            {
                // 处理错误状态码
                throw new HttpRequestException($"Error: {response.ReasonPhrase}");
            }
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine("\nException Caught!");
            Console.WriteLine("Message :{0} ", e.Message);
            return string.Empty;
        }
    }

    // 可以继续添加其他HTTP方法的异步封装，比如PUT, DELETE等
}

// 使用示例
public class Program
{
    public static async Task Main(string[] args)
    {
        var httpHelper = new HttpHelper("http://your-api-url.com");
        string result = await httpHelper.GetAsync("/api/resource");
        Console.WriteLine(result);
    }
}

这个帮助类提供了GET和POST方法的基本封装。你可以根据需要继续添加PUT、DELETE等其他HTTP方法的实现。同时，根据实际需求，你可能还需要处理HTTP请求头、错误处理、超时设置、取消操作等高级功能。