'System.Net.Http.HttpContent' does not contain a definition for 'ReadAsAsync' and no extension method

Question

I made a console app to consume a Web API I just made. The console app code does not compile. It gives me the compilation error:

'System.Net.Http.HttpContent' does not contain a definition for 
'ReadAsAsync' and no extension method 'ReadAsAsync' accepting a 
first argument of type 'System.Net.Http.HttpContent' could be 
found (are you missing a using directive or an assembly reference?)

Here's a test method in which this error occurs.

static IEnumerable<Foo> GetAllFoos()
{
  using (HttpClient client = new HttpClient())
  {
    client.DefaultRequestHeaders.Add("appkey", "myapp_key");

    var response = client.GetAsync("http://localhost:57163/api/foo").Result;

    if (response.IsSuccessStatusCode)
      return response.Content.ReadAsAsync<IEnumerable<Foo>>().Result.ToList();
  }

  return null;
}

I have used this method and consumed it from an MVC client.

Water Cooler v2 · Accepted Answer · 2013-01-25 12:53:09Z

168

After a long struggle, I found the solution.

Solution: Add a reference to System.Net.Http.Formatting.dll. This assembly is also available in the C:\Program Files\Microsoft ASP.NET\ASP.NET MVC 4\Assemblies folder.

The method ReadAsAsync is an extension method declared in the class HttpContentExtensions, which is in the namespace System.Net.Http in the library System.Net.Http.Formatting.

Reflector came to rescue!

answered Jan 25, 2013 at 12:53

Water Cooler v2

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6 Comments

bladefist Over a year ago

How did you get that folder there? I used the web platform installer and it didn't make that folder in Program Files.

FrankO Over a year ago

Add Reference -> Assemblies -> Extensions. If it is not listed, go to the Search Assemblies box and type 'formatting'. Hopefully that finds it easier for you.

PurpleSmurph Over a year ago

An update, I found mine here: C:\Program Files (x86)\Microsoft ASP.NET\ASP.NET MVC 4\Packages\Microsoft.AspNet.WebApi.Client.4.0.30506.0\lib\net40

WernerCD Over a year ago

nuget.org/packages/System.Net.Http.Formatting.Extension - any reason not to use this?

Ashique Razak Over a year ago

Just install this package System.Net.Http.Formatting.Extension from NuGet

|

Rikin Patel · Accepted Answer · 2015-12-20 16:41:26Z

137

Make sure that you have installed the correct NuGet package in your console application:

<package id="Microsoft.AspNet.WebApi.Client" version="4.0.20710.0" />

and that you are targeting at least .NET 4.0.

This being said, your GetAllFoos function is defined to return an IEnumerable<Prospect> whereas in your ReadAsAsync method you are passing IEnumerable<Foo> which obviously are not compatible types.

Install-Package Microsoft.AspNet.WebApi.Client

edited Dec 20, 2015 at 16:41

Rikin Patel

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answered Jan 25, 2013 at 11:26

Darin Dimitrov

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14 Comments

Water Cooler v2 Over a year ago

Thanks. That was a slip, a left over from my effort to remove business related code and replace it with Foos.

Water Cooler v2 Over a year ago

I don't understand. I am already targeting the .NET 4.0 framework in my Console app properties. Do I need to set a reference to this library Microsoft.AspNet.WebAPI.Client.dll? I never set any such reference in the ASP.NET MVC project that also consume my Web API and works just fine.

Darin Dimitrov Over a year ago

You need to install the Microsoft.AspNet.WebApi.Client NuGet. This will download the latest version from the internet and reference the assembly in your console application. That's exactly what the ASP.NET MVC project template does and is the reason why you don't need to install anything for it to work. But in your console application there's no such thing.

Water Cooler v2 Over a year ago

Thanks. I did what you said. I have 12 projects in my solution, but for some strange reason, after I said 'install-package Microsoft.AspNet.WebApi.Client' in the Library Package Manager console, it printed its usual trace and then said 'Successfully installed Microsoft.AspNet.WebApi.Client in MyMVCProjectNameAndNotMyConsoleProjectName'. The next time I selected my Console project and typed the same thing in the package manager console. It said MyMVCProjectName already references Microsoft.AspNet.WebApi.Client. I am confused.

Darin Dimitrov Over a year ago

Yeah me too. Start from scratch. New console application, open up the NuGet console, type Install-Package Microsoft.AspNet.WebApi.Client and try the code.

|

Kasun Ganganath Rathnasekara · Accepted Answer · 2017-10-07 14:21:34Z

39

if you unable to find assembly reference from when (Right click on reference ->add required assembly)

try this Package manager console
Install-Package System.Net.Http.Formatting.Extension -Version 5.2.3 and then add by using add reference .

answered Oct 7, 2017 at 14:21

Kasun Ganganath Rathnasekara

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1 Comment

AKS Over a year ago

I was migrating dotnetcore application from 2.2 to 3.1 latest and encounter this error.My app already having reference to System.Net.Http.Formatting.Extension v5.2.3 but my app complain this error , so I installed nuget package Microsoft.AspNet.WebApi.Client as suggested by Rikin and Darin and after that issue is resolved. Thanks

Conor Kelly · Accepted Answer · 2016-02-05 13:59:39Z

Adding a reference to System.Net.Http.Formatting.dll may cause DLL mismatch issues. Right now, System.Net.Http.Formatting.dll appears to reference version 4.5.0.0 of Newtonsoft.Json.DLL, whereas the latest version is 6.0.0.0. That means you'll need to also add a binding redirect to avoid a .NET Assembly exception if you reference the latest Newtonsoft NuGet package or DLL:

<dependentAssembly>
   <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
    <bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0" />
 </dependentAssembly>

So an alternative solution to adding a reference to System.Net.Http.Formatting.dll is to read the response as a string and then desearalize yourself with JsonConvert.DeserializeObject(responseAsString). The full method would be:

public async Task<T> GetHttpResponseContentAsType(string baseUrl, string subUrl)
{
     using (var client = new HttpClient())
     {
         client.BaseAddress = new Uri(baseUrl);
         client.DefaultRequestHeaders.Accept.Clear();
         client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

         HttpResponseMessage response = await client.GetAsync(subUrl);
         response.EnsureSuccessStatusCode();
         var responseAsString = await response.Content.ReadAsStringAsync();
         var responseAsConcreteType = JsonConvert.DeserializeObject<T>(responseAsString);
         return responseAsConcreteType;
      }
}

Ram · Accepted Answer · 2013-10-24 13:31:11Z

9

or if you have VS 2012 you can goto the package manager console and type Install-Package Microsoft.AspNet.WebApi.Client

This would download the latest version of the package

answered Oct 24, 2013 at 13:31

Ram

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2 Comments

Dan Rayson Over a year ago

This fixed it for me. - using VS2013

Naveen Over a year ago

if you already have a Microsoft.AspNet.WebApi.Client package try un installing and installing it, that fixed my issue for v 5.2.3

Hisham Shahid · Accepted Answer · 2021-11-24 04:34:57Z

5

Install below package from nuget

answered Nov 24, 2021 at 4:34

Hisham Shahid

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Comments

Natalija · Accepted Answer · 2021-06-15 11:37:09Z

4

Had the same issue, but proposed answers didn't help, installing System.Net.Http.Json package removed the error.

answered Jun 15, 2021 at 11:37

Natalija

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Comments

Debendra Dash · Accepted Answer · 2016-07-09 05:47:22Z

-2

USE This Assembly Referance in your Project

Add a reference to System.Net.Http.Formatting.dll

answered Jul 9, 2016 at 5:47

Debendra Dash

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1 Comment

user247702 Over a year ago

The accepted answer from January 2013 already explains this and has more information. Your answer is also not properly formatted.

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