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 defin

Answer 1

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

Answer 2

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.

Answer 3

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).

Answer 4

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.

Answer 5

Just expanding Jeroen's answer with the tips in comments:

var content = new StringContent(
    JsonConvert.SerializeObject(user), 
    Encoding.UTF8, 
    MediaTypeNames.Application.Json);

var response = await client.PostAsync("api/AgentCollection", content);

Answer 6

For me I found the solution after a lot of try which is replacing

HttpClient

with

System.Net.Http.HttpClient