要在.NET Framework 4.5中进行外部API的POST请求，你可以使用HttpClient类。

1. Post请求

using System;
using System.Net.Http;
using System.Threading.Tasks;class Program
{static async Task Main(string[] args){// 创建一个HttpClient实例using (HttpClient client = new HttpClient()){try{// 创建请求的内容var requestData = new { Name = "John", Age = 30 };var content = new StringContent(JsonConvert.SerializeObject(requestData), System.Text.Encoding.UTF8, "application/json");// 发起POST请求并获取响应HttpResponseMessage response = await client.PostAsync("https://api.example.com/some-endpoint", content);// 确认请求成功response.EnsureSuccessStatusCode();// 读取响应内容string responseBody = await response.Content.ReadAsStringAsync();// 处理响应数据Console.WriteLine(responseBody);}catch (HttpRequestException e){// 处理请求异常Console.WriteLine($"请求异常: {e.Message}");}}}
}

另外，post传参还有另外一种方式，使用FormUrlEncodedContent：

var content = new FormUrlEncodedContent(new Dictionary<string, string>(){{"empid", "E01930"},});

2. Get请求

// 创建一个HttpClient实例
using (HttpClient client = new HttpClient())
{
// 设置API的URL
string apiUrl = "http://nhbsapt01:801/accountreviewautoupdate";
string fullUrl = apiUrl + "?empid=" + "A00001";try
{// 发送POST请求并获取响应// HttpResponseMessage response = client.PostAsync(apiUrl, content).Result;HttpResponseMessage response = client.GetAsync(fullUrl).Result;// 确保请求成功response.EnsureSuccessStatusCode();// 读取响应内容string responseBody = response.Content.ReadAsStringAsync().Result;// 处理响应数据Console.WriteLine(responseBody);
}
catch (Exception ex)
{Console.WriteLine("Error: " + ex.Message);
}

3. 奇葩(post请求url传参)

// 创建一个HttpClient实例
using (HttpClient client = new HttpClient())
{// 设置API的URLstring apiUrl = "http://nhbsapt01:801/accountreviewautoupdate";string fullUrl = apiUrl + "?empid=" + "A00001";// 构造要发送的参数var postData = new Dictionary<string, string>{{ "empid", "A00001" },};// 将参数转换为表单编码格式var content = new FormUrlEncodedContent(postData);try{// 发送POST请求并获取响应// HttpResponseMessage response = client.PostAsync(apiUrl, content).Result;HttpResponseMessage response = client.PostAsync(fullUrl,content).Result;// 确保请求成功response.EnsureSuccessStatusCode();// 读取响应内容string responseBody = response.Content.ReadAsStringAsync().Result;// 处理响应数据Console.WriteLine(responseBody);}catch (Exception ex){Console.WriteLine("Error: " + ex.Message);}