ASP.NET Web API框架的哪一部分将用户定义的对象转换为HttpResponseMessage？

Question

If you have a action in an ApiController like so:

public Foo GetFoo(int id)
{
  // ...
}

And from another .NET application of any type, you call this API end-point like so:

using (var client = new HttpClient())
{
    var response = await client.PostAsJsonAsync("http://localhost/api/foo/1", value);

    // ...
}

Then, the HttpClient.PostAsJsonAsync method returns a Task<HttpResponseMessage> even when the API action returned a user-defined object of class Foo .

What part of the Web API does this translation? Does the client code always receive a HttpResponseMessage ?

Answer 1

HttpClient doesn't know that the response maps to the foo class. It simply returns the HTTP response encapsulated as a HttpResponseMessage.

If you want to map the response to a Foo object you must tell it to do so.

Example:

using (var client = new HttpClient())
{
    var response = await client.PostAsJsonAsync("http://localhost/api/foo/1", value);
    var stream = await response.Content.ReadAsStreamAsync(); // Read the request body into a stream.
    // Map the body to a object of type Foo
    var foo = new JsonMediaTypeFormatter().ReadFromStream(typeof(Foo), stream, Encoding.UTF8, null);

    // Do whatever you want with foo...

}