命名空间“System.Net”中不存在类型或命名空间名称“Http”（您是否缺少程序集引用？）

Question

我正在尝试按照复数视频中的示例进行操作

https://app.pluralsight.com/player?course=aspdotnet-5-ef7-bootstrap-angular-web-app&author=shawn-wildermuth&name=aspdotnet-5-ef7-bootstrap-angular-web-app-m7&clip=8&mode=live&start=2

当我尝试完成 Api 添加坐标时出现错误：

命名空间“System.Net”中不存在类型或命名空间名称“Http”（您是否缺少程序集引用？）

这发生在以下课程中：

using Microsoft.Extensions.Logging;
using System.Net;
using System.Threading.Tasks;
using Newtonsoft.Json.Linq;
using System.Net.Http;

namespace Moran.Services
{
    public class CoordService
    {
        private ILogger<CoordService> _logger;

        public CoordService(ILogger<CoordService> logger)
        {
            _logger = logger;
        }

        public async Task<CoordServiceResult> Lookup(string location)
        {
            var result = new CoordServiceResult()
            {
                Success = false,
                Message = "Undetermined failures while looking up coordinates"
            };
            //Lookup Coordinates
            var bingKey = Startup.Configuration["AppSettings:BingKey"];
            var encodedName = WebUtility.UrlEncode(location);
            var url = $"http://dev.virtualearth.net/REST/v1/Locations?q={encodedName}&key={bingKey}";

            var client = new HttpClient();

            var json = await client.GetStringAsync(url);

            // Read out the results
            // Fragile, might need to change if the Bing API changes
            var results = JObject.Parse(json);
            var resources = results["resourceSets"][0]["resources"];
            if (!resources.HasValues)
            {
                result.Message = $"Could not find '{location}' as a location";
            }
            else
            {
                var confidence = (string)resources[0]["confidence"];
                if (confidence != "High")
                {
                    result.Message = $"Could not find a confident match for '{location}' as a location";
                }
                else
                {
                    var coords = resources[0]["geocodePoints"][0]["coordinates"];
                    result.Latitude = (double)coords[0];
                    result.Longitude = (double)coords[1];
                    result.Success = true;
                    result.Message = "Success";
                }
            }
            return result;
        }
    }
}

当我尝试添加时发生这种情况

var client = new HttpClient();

知道为什么会这样吗？

我找不到任何无法编译的原因......

Answer 1

HttpClient 类驻留在System.Net.Http 命名空间中，该命名空间在System.Net.Http.dll 中。要在 ASP.NET 5 项目中使用此类，您需要将 System.Net.Http 添加到 project.json 文件中 json 数据的 "dependencies" 部分

  "dependencies": {    
    "Microsoft.AspNet.Diagnostics": "1.0.0-beta5",
    "Microsoft.AspNet.Mvc": "6.0.0-beta5",
    "Microsoft.AspNet.Mvc.TagHelpers": "6.0.0-beta5",
    "Microsoft.AspNet.Server.IIS": "1.0.0-beta5",
    "Microsoft.AspNet.Server.WebListener": "1.0.0-beta5",
    "Microsoft.AspNet.StaticFiles": "1.0.0-beta5",
    "Microsoft.AspNet.Tooling.Razor": "1.0.0-beta5",
    "Microsoft.Framework.Configuration.Json": "1.0.0-beta5",
    "Microsoft.Framework.Logging": "1.0.0-beta5",
    "Microsoft.Framework.Logging.Console": "1.0.0-beta5",

    "System.Net.Http": "4.0.1-beta-23409"

  },

4.0.1-beta-23409 是撰写本文时的最新版本。 Visual Studio intellisense 将为您提供多个可用版本，您可以选择最新/稳定的。

进行此更改后，当您保存文件时，它将执行 dnu restore（通常会根据需要下载必要的软件包）并添加对System.Net.Http 程序集。您可以在类中添加 using 语句并开始使用 HttpClient 类。

using System;
using System.Net.Http;
public class SomeClass
{
  public void SomeMethod()
  {
     var client = new HttpClient();
  }
}