c# WebClient，HttpClient 发送请求出错时解决办法

在C# 使用 HttpClient或 WebClient发送请求时

提示  ：

请求被中止: 未能创建 SSL/TLS 安全通道

或

发送请求时出错

的问题

解决办法：在发送请求地址代码前加如下代码

System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;（ | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;）

问题解决！

如：

            HttpClient httpClient = new HttpClient()；
           System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
            var res = await httpClient.GetAsync(url);
            var contentStr = await res.Content.ReadAsStringAsync();

或者：

handler = new HttpClientHandler() ;
handler.AllowAutoRedirect = true;
handler.UseCookies = true;
handler.CookieContainer = cookies;

handler.ClientCertificateOptions = ClientCertificateOption.Automatic;

httpClient = new HttpClient(handler);