How do I pass an object to HttpClient PostAsync and serialize as a JSON body

Question

I m using System Net Http  I found several examples on the web  I managed to create this code for make a POST request   public static string POST string resource  string token        using  var client   new HttpClient                  client BaseAddress   new Uri baseUri           client DefaultRequestHeaders Add  token   token            var content   new FormUrlEncodedContent new                          new KeyValuePair lt string  string gt                               var result   client PostAsync     content  Result          string resultContent   result Content ReadAsStringAsync   Result          return resultContent             all working fine  But suppose that I want pass a third param to the POST method  a param called data  The data param is an object like this   object data   new       name    Foo       category    article       how can I do that without create the KeyValuePair  My php RestAPI wait a json input  so the FormUrlEncodedContent should send the raw json correctly  But how can I do this with Microsoft Net Http  Thanks

User · Answer

There s now a simpler way with  NET Standard or  NET Core   var client   new HttpClient    var response   await client PostAsync uri  myRequestObject  new JsonMediaTypeFormatter       NOTE  In order to use the JsonMediaTypeFormatter class  you will need to install the Microsoft AspNet WebApi Client NuGet package  which can be installed directly  or via another such as Microsoft AspNetCore App   Using this signature of HttpClient PostAsync  you can pass in any object and the JsonMediaTypeFormatter will automatically take care of serialization etc   With the response  you can use HttpContent ReadAsAsync lt T gt  to deserialize the response content to the type that you are expecting   var responseObject   await response Content ReadAsAsync lt MyResponseType gt

User · Answer

A simple solution is to use Microsoft ASP NET Web API 2 2 Client from NuGet   Then you can simply do this and it ll serialize the object to JSON and set the Content-Type header to application json  charset utf-8   var data   new       name    Foo       category    article      var client   new HttpClient    client BaseAddress   new Uri baseUri   client DefaultRequestHeaders Add  token   token   var response   await client PostAsJsonAsync     data

User · Answer

arad good point   In fact I just found this extension method   NET 5 0   PostAsJsonAsync lt TValue gt  HttpClient  String  TValue  CancellationToken  from https   docs microsoft com en-us dotnet api system net http json httpclientjsonextensions postasjsonasync view net-5 0 So one can now  var data   new   foo    quot Hello quot   bar   42     var response   await  Client PostAsJsonAsync  Uri  data  cancellationToken

User · Answer

You need to pass your data in the request body as a raw string rather than FormUrlEncodedContent  One way to do so is to serialize it into a JSON string   var json   JsonConvert SerializeObject data      or JsonSerializer Serialize if using System Text Json   Now all you need to do is pass the string to the post method   var stringContent   new StringContent json  UnicodeEncoding UTF8   application json       use MediaTypeNames Application Json in Core 3 0  and Standard 2 1   var client   new HttpClient    var response   await client PostAsync uri  stringContent

User · Answer

The straight up answer to your question is  No   The signature for the PostAsync method is as follows       public Task PostAsync Uri requestUri  HttpContent content    So  while you can pass an object to PostAsync it must be of type HttpContent and your anonymous type does not meet that criteria   However  there are ways to accomplish what you want to accomplish   First  you will need to serialize your anonymous type to JSON  the most common tool for this is Json NET   And the code for this is pretty trivial   var myContent   JsonConvert SerializeObject data     Next  you will need to construct a content object to send this data  I will use a ByteArrayContent object  but you could use or create a different type if you wanted   var buffer   System Text Encoding UTF8 GetBytes myContent   var byteContent   new ByteArrayContent buffer     Next  you want to set the content type to let the API know this is JSON   byteContent Headers ContentType   new MediaTypeHeaderValue  application json      Then you can send your request very similar to your previous example with the form content   var result   client PostAsync     byteContent  Result   On a side note  calling the  Result property like you re doing here can have some bad side effects such as dead locking  so you want to be careful with this

User · Answer

New  NET 5 Solution  In  NET 5  a new class has been introduced called JsonContent  which derives from HttpContent  See in Microsoft docs This class has a static method called Create    which takes an object as a parameter  Usage  var myObject   new       foo    quot Hello quot       bar    quot World quot       JsonContent content   JsonContent Create myObject    HttpResponseMessage response   await  httpClient PostAsync  quot https       quot   content

[c#] How do I pass an object to HttpClient.PostAsync and serialize as a JSON body?

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