框架 .NET Core 3.1

HttpClient ：Provides a base class for sending HTTP requests and receiving HTTP responses from a resource identified by a URI.

通俗点说

HttpClient是用来发http请求并获取结果内容的。

ContentType是用来指定请求内容的数据格式的，比如：application/x-www-form-urlencoded 和 application/json。

话不多说，下面看一下怎么用。

application/x-www-form-urlencoded

application/x-www-form-urlencoded 对应的ContentType类型是FormUrlEncodedContent，FormUrlEncodedContent 构造函数需要一个键值对类型的参数，放Dictionary<string, string>这样的就行。

数据格式就是URL传参那样：account=test&password=test123

代码如下，简单好用 

public static async Task<string> PostUrlencodedAsync(string url, Dictionary<string, string> dic)
{
    using (HttpClient _httpClient = new HttpClient())
    {
        HttpContent httpContent = new FormUrlEncodedContent(dic);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
        var response = await _httpClient.PostAsync(url, httpContent);
        return await response.Content.ReadAsStringAsync();
    }
}

application/json

application/json 对应的ContentType类型是StringContent，StringContent构造函数需要一个json字符串类型的参数，就是一个object或者List集合啥的转字符串就行。

如果需要传参，像是带个token啥放在请求头里面。

直接用键值对的方式传进来，然后循环加到请求头，方便快捷。

public static async Task<string> PostJsonAsync(string url, string jsonData, Dictionary<string, string> dic)
{
    using (HttpClient _httpClient = new HttpClient())
    {
        HttpContent httpContent = new StringContent(jsonData);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        if (dic.Count > 0)
        {
            foreach (var item in dic)
            {
                _httpClient.DefaultRequestHeaders.Add(item.Key, item.Value);
            }
        }
        var response = await _httpClient.PostAsync(url, httpContent);
        return await response.Content.ReadAsStringAsync();
    }
}

印象中以前要弄个http请求啥的，记得要写一堆代码，现在HttpClient就几行代码搞定，舒服。。。