该方法在 System.Net.Http.Formatting 程序集中定义，该程序集通过NuGet分发。令人困惑的是，NuGet包名称是 Microsoft.AspNet.WebApi.Client ：



NuGet Gallery | Microsoft.AspNet.WebApi.Client 5.2.7 [ ^ ]



注意： async 转换您的方法不应该调用 .Result ：

  public   static   async 任务< List< tblusertype>> GetAll（）
 {
 string  apiHost = ConfigurationManager.AppSettings [  ApiHost跨度>]; 
使用（ var  client =  new  HttpClient（））
 {
 client.BaseAddress =  new  Uri（apiHost）; 
 client.DefaultRequestHeaders.Accept.Add（ new  MediaTypeWithQualityHeaderValue（ 应用/ JSON跨度>））; 

使用（ var  response =  await  client.GetAsync（  api / UserType））
 { 
 if （！response.IsSuccessStatusCode） return  空跨度>; 
 return   await  response.Content.ReadAsAsync< List< tblusertype>>（）; 
} 
} 
} 

另外：你正在使用HttpClient错误，这会破坏你的软件稳定性ASP.NET Monsters [ ^ 一>

In my project, I am calling webapi services - Get action from controller of another project. My code is:

using System.Net.Http;
using System.Configuration;
using System.Net.Http.Headers;

public ActionResult Index()
       {
           ViewBag.Place = new SelectList(GetPlaces(), "ID", "PlaceName");

           FlightDetails flightDetails = new FlightDetails();
           flightDetails.DepartureDate = System.DateTime.Now;
           flightDetails.ReturnDate = System.DateTime.Now;
           return View(flightDetails);
       }

private List<tblPlace> GetPlaces()
{
    List<tblPlace> lstPlaces = new List<tblPlace>(); //to be uncommented

    //lstPlaces = TwentyFour7Sewa.Utils.APIEngine<tblPlace>.GetAll("api/fromto");
    using (var client = new HttpClient())
    {
        string apiHost = ConfigurationManager.AppSettings["ApiHost"];
        string apiDirectory = "api/fromto";

        List<tblPlace> result = new List<tblPlace>();
        client.BaseAddress = new Uri(apiHost);
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        HttpResponseMessage response = client.GetAsync(apiDirectory).Result;

        if (response.IsSuccessStatusCode)
        {
            result = response.Content.ReadAsAsync<List<tblPlace>>().Result;
            return result;
        }
        else
        {
            return null;
        }
    }

    //lstPlaces = lstPlaces.OrderBy(o => o.PlaceName).ToList<tblPlace>();
    //return lstPlaces;
}

However, in line

ViewBag.Place = new SelectList(GetPlaces(), "ID", "PlaceName");

in Index() actionresult, I am getting error,

System.MissingMethodException: 'Method not found: 'System.Threading.Tasks.Task`1<!!0> System.Net.Http.HttpContentExtensions.ReadAsAsync(System.Net.Http.HttpContent)'.'

Web api is returning required value. The issue is with line

ReadAsAsync

. I did nothing on this part of code. It was working fine till yesterday. All of a sudden what happened, I have no clue.

What I have tried:

Found somewhere that I need to use Microsoft.Net.Http instead of System.Net.Http since this is obsolete. When I installed

Microsoft.Net.Http 

from nuget package in this project, this dll was not shown in project reference.

That method is defined in the System.Net.Http.Formatting assembly, which is distributed via NuGet. Confusingly, the NuGet package name is Microsoft.AspNet.WebApi.Client:

NuGet Gallery | Microsoft.AspNet.WebApi.Client 5.2.7[^]

NB: The async conversion of your method should not call .Result at all:

public static async Task<List<tblusertype>> GetAll()
{
    string apiHost = ConfigurationManager.AppSettings["ApiHost"];
    using (var client = new HttpClient())
    {
        client.BaseAddress = new Uri(apiHost);
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        
        using (var response = await client.GetAsync("api/UserType"))
        {
            if (!response.IsSuccessStatusCode) return null;
            return await response.Content.ReadAsAsync<List<tblusertype>>();
        }
    }
}

Also: You're using HttpClient wrong and it is destabilizing your software | ASP.NET Monsters[^]