构建时Youtube API v3 System.Threading.Tasks.dll错误

Question

我正在尝试使用从谷歌提供的示例中获取的Youtube API v3搜索示例，但在尝试构建时我收到此错误。

错误1类型＆＃39; System.Threading.Tasks.Task`1＆＃39;在未引用的程序集中定义。您必须添加对程序集的引用，System.Threading.Tasks，Version = 1.5.11.0，Culture = neutral，PublicKeyToken = b03f5f7f11d50a3a＆＃39;。

不确定如何解决此问题，我发现同样的问题here，但没有解决方案。

感谢您的帮助!!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using System.Reflection;
using System.Threading;
using System.Threading.Tasks;
using System.Data;
using System.Collections;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Services;
using Google.Apis.Upload;
using Google.Apis.Util.Store;
using Google.Apis.YouTube.v3;
using Google.Apis.YouTube.v3.Data;    
namespace Google.Apis.YouTube.Samples
    {
        /// <summary>
        /// YouTube Data API v3 sample: search by keyword.
        /// Relies on the Google APIs Client Library for .NET, v1.7.0 or higher.
        /// See https://code.google.com/p/google-api-dotnet-client/wiki/GettingStarted
        ///
        /// Set ApiKey to the API key value from the APIs & auth > Registered apps tab of
        ///   https://cloud.google.com/console
        /// Please ensure that you have enabled the YouTube Data API for your project.
        /// </summary>
        internal class Search
        {

            static void Main(string[] args)
            {
                Console.WriteLine("YouTube Data API: Search");
                Console.WriteLine("========================");

                try
                {
                    new Search().Run().Wait();
                }
                catch (AggregateException ex)
                {
                    foreach (var e in ex.InnerExceptions)
                    {
                        Console.WriteLine("Error: " + e.Message);
                    }
                }

                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }

            private async Task Run()
            {
                var youtubeService = new YouTubeService(new BaseClientService.Initializer()
                {
                    ApiKey = "REPLACE_ME",
                    ApplicationName = this.GetType().ToString()
                });

                var searchListRequest = youtubeService.Search.List("snippet");
                searchListRequest.Q = "Google"; // Replace with your search term.
                searchListRequest.MaxResults = 50;

                // Call the search.list method to retrieve results matching the specified query term.
                var searchListResponse = await searchListRequest.ExecuteAsync();

                List<string> videos = new List<string>();
                List<string> channels = new List<string>();
                List<string> playlists = new List<string>();

                // Add each result to the appropriate list, and then display the lists of
                // matching videos, channels, and playlists.
                foreach (var searchResult in searchListResponse.Items)
                {
                    switch (searchResult.Id.Kind)
                    {
                        case "youtube#video":
                            videos.Add(String.Format("{0} ({1})", searchResult.Snippet.Title, searchResult.Id.VideoId));
                            break;

                        case "youtube#channel":
                            channels.Add(String.Format("{0} ({1})", searchResult.Snippet.Title, searchResult.Id.ChannelId));
                            break;

                        case "youtube#playlist":
                            playlists.Add(String.Format("{0} ({1})", searchResult.Snippet.Title, searchResult.Id.PlaylistId));
                            break;
                    }
                }

                Console.WriteLine(String.Format("Videos:\n{0}\n", string.Join("\n", videos)));
                Console.WriteLine(String.Format("Channels:\n{0}\n", string.Join("\n", channels)));
                Console.WriteLine(String.Format("Playlists:\n{0}\n", string.Join("\n", playlists)));
            }
        }
    }