.net 4.0 中不存在 HttpClient：我该怎么办？

好吧，我编辑了我的代码，我没有收到错误，但 messageBox.Show 没有返回任何空框。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Globalization;
using System.IO;
using System.Net;
using System.Web;
using System.Web.Script.Serialization;




namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        private JavaScriptSerializer _Serializer = new JavaScriptSerializer();

        public Form1()
        {
            InitializeComponent();
            string f = TranslateText("hi", "English", "German", "", "");
            MessageBox.Show(f);
        }

        private void Form1_Load(object sender, EventArgs e)
        {
        }

        public string TranslateText(string inputText, string sourceLanguage, string destinationLanguage, string referrer, string apiKey)
        {
                string requestUrl = string.Format(
                    "http://ajax.googleapis.com/ajax/services/language/translate?v=1.0&q={0}&langpair={1}|{2}&key={3}", 
                    HttpUtility.UrlEncode(inputText), 
                    sourceLanguage.ToLowerInvariant(), 
                    destinationLanguage.ToLowerInvariant(), 
                    apiKey
                );

                try
                {
                    HttpWebRequest http = (HttpWebRequest)HttpWebRequest.Create(requestUrl);
                    http.Referer = referrer;
                    HttpWebResponse response = (HttpWebResponse)http.GetResponse();
                    using (StreamReader sr = new StreamReader(response.GetResponseStream()))
                    {
                        string responseJson = sr.ReadToEnd();
                        var translation = this._Serializer.Deserialize<Milkshake.Integration.Google.GoogleAjaxResponse<Milkshake.Integration.Google.Translate.TranslationResponse>>(responseJson);

                        if (translation != null && translation.ResponseData != null && translation.ResponseData.ResponseStatus == HttpStatusCode.OK)
                        {
                            return translation.ResponseData.TranslatedText;
                        }
                        else
                        {
                            return String.Empty;
                        }
                    }
                }
            catch
                {
                    return String.Empty;
            }
        }
    }
}

答案

• 您可以使用WebClient。

• 或者（如果您需要对请求进行更细粒度的控制）HttpWebRequest

• 或者，HttpClient在 System.Net.Http.dll 中。

这是对 HttpWebRequest 的"翻译"（需要而不是 WebClient 来设置引荐来源网址）。

    HttpWebRequest http = (HttpWebRequest)HttpWebRequest.Create(requestUrl))
    http.Referer = referrer;
    HttpWebResponse response = (HttpWebResponse )http.GetResponse();
    using (StreamReader sr = new StreamReader(response.GetResponseStream()))
    {
        string responseJson = sr.ReadToEnd();
        // more stuff
    }

来自: stackoverflow.com