如何用HttpClient替换WebClient？

Question

我的asp中有以下WebClient。net mvc web应用程序：

using (WebClient wc = new WebClient()) // call the Third Party API to get the account id 
{
     string url = currentURL + "resources/" + ResourceID + "/accounts?AUTHTOKEN=" + pmtoken;
     var json = await wc.DownloadStringTaskAsync(url);
 }

那么，有人可以建议我如何将它从WebClient更改为HttpClient吗？

Answer 1

您可以编写以下代码：

string url = 'some url';

// best practice to create one HttpClient per Application and inject it
HttpClient client = new HttpClient();

using (HttpResponseMessage response = client.GetAsync(url).Result)
{
    using (HttpContent content = response.Content)
    {
         var json = content.ReadAsStringAsync().Result;
    }
}

更新1：

如果您想用wait关键字替换对Result属性的调用，那么这是可能的，但您必须将此代码放入标记为async的方法中，如下所示

public async Task AsyncMethod()
{
    string url = 'some url';

    // best practice to create one HttpClient per Application and inject it
    HttpClient client = new HttpClient();

    using (HttpResponseMessage response = await client.GetAsync(url))
    {
        using (HttpContent content = response.Content)
        {
           var json = await content.ReadAsStringAsync();
        }
     }
}

如果您错过了方法中的async关键字，您可能会得到一个编译时错误，如下所示

“等待”运算符只能在异步方法中使用。考虑使用异步修饰符标记此方法，并将其返回类型更改为任务

更新2：

回答您关于将'WebClient'转换为'WebRequest'的原始问题，这是您可以使用的代码，...但是微软（和我）推荐你使用第一种方法（通过使用HttpClient）。

string url = currentURL + "resources/" + ResourceID + "/accounts?AUTHTOKEN=" + pmtoken;

HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
httpWebRequest.Method = "GET";

using (WebResponse response = httpWebRequest.GetResponse())
{
     HttpWebResponse httpResponse = response as HttpWebResponse;
     using (StreamReader reader = new StreamReader(httpResponse.GetResponseStream()))
     {
         var json = reader.ReadToEnd();
     }
}

如果使用C#8及以上版本，那么就可以编写非常优雅的代码

public async Task AsyncMethod()
{
    string url = 'some url';

    // best practice to create one HttpClient per Application and inject it
    HttpClient client = new HttpClient();

    using HttpResponseMessage response = await client.GetAsync(url);
    using HttpContent content = response.Content;
    var json = await content.ReadAsStringAsync();
}   // dispose will be called here, when you exit of the method, be aware of that

更新3

要了解为什么建议使用isHttpClient而不是WebRequest和WebClient，您可以参考以下链接。

在HttpClient和WebClient之间做出决定

http://www.diogonunes.com/blog/webclient-vs-httpclient-vs-httpwebrequest/

HttpClient与HttpWebRequest

中的WebClient和HTTPWebRequest类之间有什么区别。网

http://blogs.msdn.com/b/henrikn/archive/2012/02/11/httpclient-is-here.aspx