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

User · Answer

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

User · Answer

Try to install in your project the NuGet Package   Microsoft AspNet WebApi Client   Install-Package Microsoft AspNet WebApi Client

User · Answer

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

User · Answer

I know this reply is too late  I had the same issue and i was adding the System Net Http Formatting Extension Nuget  after checking here and there I found that the Nuget is added but the System Net Http Formatting dll was not added to the references  I just reinstalled the Nuget

User · Answer

Instead of writing this amount of code to make a simple call  you could use one of the wrappers available over the internet   I ve written one called WebApiClient  available at NuGet    check it out   https   www nuget org packages WebApiRestService WebApiClient

User · Answer

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

User · Answer

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

User · Answer

Ok  it is apocalyptical 2020 now  and you can find these methods in NuGet package System Net Http Json  But beware that it uses System Text Json internally  And if you really need to find out which API resides where  just use https   apisof net

User · Answer

For me I found the solution after a lot of try which is replacing HttpClient  with System Net Http HttpClient

User · Answer

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 lt HttpResponseMessage gt  PostAsJsonAsync lt TModel gt  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

User · Answer

If you re playing around in Blazor and get the error  you need to add the package Microsoft AspNetCore Blazor HttpClient

User · Answer

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

User · Answer

If you are already using Newtonsoft Json try this       Alternative using WebApi Client 5 2 7       var response   await Client PutAsJsonAsync             quot api AgentCollection quot   user           requestListDto     var response   await Client PostAsync  quot api AgentCollection quot   new StringContent      JsonConvert SerializeObject user   Encoding UTF8   quot application json quot      Performance are better than JavaScriptSerializer  Take a look here https   www newtonsoft com json help html Introduction htm

[c#] HttpClient not supporting PostAsJsonAsync method C#

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