How to Pass an Object to Httpclient.Postasync and Serialize as a JSON Body

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

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.

POSTing JsonObject With HttpClient From Web API

With the new version of HttpClient and without the WebApi package it would be:

var content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");
var result = client.PostAsync(url, content).Result;

Or if you want it async:

var result = await client.PostAsync(url, content);

preparing Json Object for HttpClient Post method

You need to either manually serialize the object first using JsonConvert.SerializeObject

var values = new Dictionary<string, string> 
{
{"type", "a"}, {"card", "2"}
};
var json = JsonConvert.SerializeObject(values);
var data = new StringContent(json, Encoding.UTF8, "application/json");

//...code removed for brevity

Or depending on your platform, use the PostAsJsonAsync extension method on HttpClient.

var values = new Dictionary<string, string> 
{
{"type", "a"}, {"card", "2"}
};
var client = new HttpClient();
using(var response = client.PostAsJsonAsync(myUrl, values).Result) {
result = response.Content.ReadAsStringAsync().Result;
}

HttpClient Post request with Json body

Finally resolved this. The issue was due to me using PascalCasing inside my Json body and the end point using camelCasing so it was not able to read the property values.

So instead of this

var jSonData = JsonConvert.SerializeObject(customObj);

I had to use the camel casing resolver when I serilized my json object.

var changePassObj = JsonConvert.SerializeObject(customObj, 
new JsonSerializerSettings
{
ContractResolver = new CamelCasePropertyNamesContractResolver()
});

Send JSON via POST in C# and Receive the JSON returned?

I found myself using the HttpClient library to query RESTful APIs as the code is very straightforward and fully async'ed. To send this JSON payload:

{
"agent": {
"name": "Agent Name",
"version": 1
},
"username": "Username",
"password": "User Password",
"token": "xxxxxx"
}

With two classes representing the JSON structure you posted that may look like this:

public class Credentials
{
public Agent Agent { get; set; }

public string Username { get; set; }

public string Password { get; set; }

public string Token { get; set; }
}

public class Agent
{
public string Name { get; set; }

public int Version { get; set; }
}

You could have a method like this, which would do your POST request:

var payload = new Credentials { 
Agent = new Agent {
Name = "Agent Name",
Version = 1
},
Username = "Username",
Password = "User Password",
Token = "xxxxx"
};

// Serialize our concrete class into a JSON String
var stringPayload = JsonConvert.SerializeObject(payload);

// Wrap our JSON inside a StringContent which then can be used by the HttpClient class
var httpContent = new StringContent(stringPayload, Encoding.UTF8, "application/json");

var httpClient = new HttpClient()

// Do the actual request and await the response
var httpResponse = await httpClient.PostAsync("http://localhost/api/path", httpContent);

// If the response contains content we want to read it!
if (httpResponse.Content != null) {
var responseContent = await httpResponse.Content.ReadAsStringAsync();

// From here on you could deserialize the ResponseContent back again to a concrete C# type using Json.Net
}


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