HttpClient not supporting PostAsJsonAsync method C#

Question

I am trying to call a web API from my web application. I am using .Net 4.5 and while writing the code I am getting the error HttpClient does not contain a definition PostAsJsonAsync method.

Below is the code:

HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:51093/");
client.DefaultRequestHeaders.Accept.Add(
   new MediaTypeWithQualityHeaderValue("application/json"));
var user = new Users();
user.AgentCode = 100;
user.Remarks = "Test";
user.CollectionDate = System.DateTime.Today;
user.RemittanceDate = System.DateTime.Today;
user.TotalAmount = 1000;
user.OrgBranchID = 101;

var response = client.PostAsJsonAsync("api/AgentCollection", user).Result;

and I am getting the error message:

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

Please have a look and advice me.

Solution 1

Yes, you need to add a reference to

System.Net.Http.Formatting.dll

This can be found in the extensions assemblies area.

A good way of achieving this is by adding the NuGet package Microsoft.AspNet.WebApi.Client to your project.

Solution 2

PostAsJsonAsync is no longer in the System.Net.Http.dll (.NET 4.5.2). You can add a reference to System.Net.Http.Formatting.dll, but this actually belongs to an older version. I ran into problems with this on our TeamCity build server, these two wouldn't cooperate together.

Alternatively, you can replace PostAsJsonAsyncwith a PostAsync call, which is just part of new dll. Replace

var response = client.PostAsJsonAsync("api/AgentCollection", user).Result;

With:

var response = client.PostAsync("api/AgentCollection", new StringContent(
   new JavaScriptSerializer().Serialize(user), Encoding.UTF8, "application/json")).Result;

Note that JavaScriptSerializer is in the namespace: System.Web.Script.Serialization.

You will have to add an assembly reference in your csproj: System.Web.Extensions.dll

See https://code.msdn.microsoft.com/windowsapps/How-to-use-HttpClient-to-b9289836

Solution 3

The missing reference is the System.Net.Http.Formatting.dll. But the better solution is to add the NuGet package Microsoft.AspNet.WebApi.Client to ensure the version of the formatting dll worked with the .NET framework version of System.Net.Http in my project.

Solution 4

As already debatted, this method isn't available anymore since .NET 4.5.2. To expand on Jeroen K's answer you can make an extension method:

public static async Task<HttpResponseMessage> PostAsJsonAsync<TModel>(this HttpClient client, string requestUrl, TModel model)
{
    var serializer = new JavaScriptSerializer();
    var json = serializer.Serialize(model);
    var stringContent = new StringContent(json, Encoding.UTF8, "application/json");
    return await client.PostAsync(requestUrl, stringContent);
}

Now you are able to call client.PostAsJsonAsync("api/AgentCollection", user).

Solution 5

I had this issue too on a project I'd just checked out from source control.

The symptom was the error described above and a yellow warning triangle on a reference to System.Net.Http.Formatting

To fix this, I removed the broken reference and then used NuGet to install the latest version of Microsoft.AspNet.WebApi.Client.

View more solutions

Comments

[Sachin Pawar]

The best option is to add 'Microsoft.AspNet.WebApi.Client' .Nuget package. That's it!

[Jidheesh Rajan]

Now i am getting an error :" Could not load file or assembly 'Newtonsoft.Json, Version=4.5.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The system cannot find the file specified. "

[Allan Elder]

Go into NuGet and look up Json.NET under online packages, or you can download from here if you aren't using NuGet get it from here james.newtonking.com/json

[vikingben]

Here is the console command if anyone is looking nuget.org/packages/System.Net.Http.Formatting

[Todd H.]

Found I had to add the NuGet package "Microsoft.AspNet.WebApi.Client" to ensure the version of the formatting dll worked with the .NET framework version of "System.Net.Http" in my project.

[Todd H.]

@Yuval - I realize now that the "solution" I suggested sounded like a comment. It turns out that Andreo authored the NuGet package I suggested.

[Neutrino]

Why does referencing a standard system assembly require me to download open source stuff from random locations on the Internet in order to get it to function? Why does this even compile if it cannot resolve its dependencies? This irks me to no end!

[reggaeguitar]

@Neutrino Would you rather write the code yourself? You should be thankful that the folks at Microsoft and elsewhere have written code you can use for free

[sasha.sochka]

is there a way to use this method from UWP app?

[Alireza]

This should be the answer. The best way to do something is the correct way of it

[Gökhan Kurt]

This is the best answer so far. Do not try adding NuGet packages or dlls.

[Yar]

PM> Install-Package System.Net.Http.Formatting.Extension

[Astaar]

Totally the best answer. Selected answer is not a best practice at all, in fact Microsoft recommends not to reference DLLs

[RasikaSam]

This was the answer to me! (to my question)

[flexxxit]

how will this be added in .net4

[Vishwajit G]

@Andreo The link (webapiclient.azurewebsites.net) is now broken as on 30-Nov-2017. NuGet working link is nuget.org/packages/WebApiRestService.WebApiClient

[yu yang Jian]

It works! To install by Nuget Console enter Install-Package Microsoft.AspNet.WebApi.Client

[Andreo Romera]

Unfortunately Microsoft has ended my azure subscription and the url is no longer valid :(

[Zin Min]

After I added System.Net.Http.Formatting.Extension from NuGet, HttpClient was thrown an error. Now I am finding the root cause. Visual Studio 2017 with .NET Framework 4.7

[Thomas Schreiter]

Off topic, but I want to mention it anyways: Use await FooAsync() instead of FooAsync().Result. The latter one can deadlock. See stackoverflow.com/q/17248680/2272514 and its accepted answer. There are also good links about details.

[daviesdoesit]

To use a type instead of "application/json" you could use MediaTypeNames.Application.Json docs.microsoft.com/en-us/dotnet/api/…

[tmutton]

This helped me and is obviously preferable to installing a library via nuget. Thank you.

[Yusha]

What the answer should actually say. Nuget > Install System.Net.Http then install System.Net.Http.Formatting.Extension

[Cameron Forward]

Worked a charm - I successfully used JsonConvert.SerializeObject(user) in place of your serialiser.

[Ryanman]

This is the second time I've forgotten this answer. PostAsJsonAsync will mysteriously exclude properties from the object you're posting when serializing etc. and no amount of attribute changes etc. will fix it. You MUST serialize yourself and you MUST use the "raw" PostAsync.

[goodeye]

Great - I used this for the general idea when debugging some json from .net core 2.2. From this post stackoverflow.com/a/29843542/292060 it shows using existing Newtonsoft library to serialize (even though the post is about how that's being removed from core 3.0)

[Benj Sanders]

@Yusha I needed to add Microsoft.AspNet.WebApi.Client and System.Net.Http.Formatting.Extension, then it compiled.

[rfcdejong]

Works for me for .net framework and netcore3.1 (which uses netstandard2.0 in this library)

[rfcdejong]

2020 answer -> stackoverflow.com/a/64015973/578552

[SomeoneElse]

Actually, this is a really good demonstration of why using "one of the wrappers available over the internet" might not be a good idea. Every external dependency that a project has is one more thing that can go wrong.