MSDN给出的HttpClient使用示例

 1 using System;
 2 using System.Json;
 3 using System.Net.Http;
 4 
 5 namespace WorldBankSample
 6 {
 7     /// <summary>
 8     /// Sample download list of countries from the World Bank Data sources at http://data.worldbank.org/
 9     /// </summary>
10     class Program
11     {
12         static string _address = "http://api.worldbank.org/countries?format=json";
13 
14         static void Main(string[] args)
15         {
16             // Create an HttpClient instance
17             HttpClient client = new HttpClient();
18 
19             // Send a request asynchronously continue when complete
20             client.GetAsync(_address).ContinueWith(
21                 (requestTask) =>
22                 {
23                     // Get HTTP response from completed task.
24                     HttpResponseMessage response = requestTask.Result;
25 
26                     // Check that response was successful or throw exception
27                     response.EnsureSuccessStatusCode();
28 
29                     // Read response asynchronously as JsonValue and write out top facts for each country
30                     response.Content.ReadAsAsync<JsonArray>().ContinueWith(
31                         (readTask) =>
32                         {
33                             Console.WriteLine("First 50 countries listed by The World Bank...");
34                             foreach (var country in readTask.Result[1])
35                             {
36                                 Console.WriteLine("   {0}, Country Code: {1}, Capital: {2}, Latitude: {3}, Longitude: {4}",
37                                     country.Value["name"],
38                                     country.Value["iso2Code"],
39                                     country.Value["capitalCity"],
40                                     country.Value["latitude"],
41                                     country.Value["longitude"]);
42                             }
43                         });
44                 });
45 
46             Console.WriteLine("Hit ENTER to exit...");
47             Console.ReadLine();
48         }
49     }
50 }

其中涉及了异步的操作，可以在以后的工作中加以借鉴。

注释：

ContinueWith是Task对象的一个方法。ContinueWith接受一个参数，这个参数是Action<T>，而Action<T>是委托，指向一个有一个参数、无返回值的方法。当然参数的类型是由T给出的。具体的来说，这里ContinueWith的参数类型是Action<Task>，且这个Task类型的参数是自动传递的。例子里给出了两个匿名方法来实现委托，都无返回值，参数是Task类型，参数由ContinueWith前面方法返回的Task自动传入。