FormUrlEncodedMediaTypeFormatter vs JQueryMvcFormUrlEncodedFormatter - asp.net-web-api

Question

I have created a default web api project with at least those 2 media formatters loaded. Both are for the same content-type:
FormUrlEncodedMediaTypeFormatter: application/x-www-form-urlencoded
JQueryMvcFormUrlEncodedFormatter: application/x-www-form-urlencoded
When I do a simple http post form with enctype="application/x-www-form-urlencoded" it works only with the JQueryMvcFormUrlEncodedFormatter, that means my sent complex object is not null at server side.
When I remove the formatter JQueryMvcFormUrlEncodedFormatter at application startup and do the simple http post form again I expect it to work again but it does not.
I get an exception that no appropriate formatter is loaded.
Thats not true -actually-
Why does it not work?
P.S.
I found that this is the difference:
– System.Net.Http.Formatting.FormUrlEncodedMediaTypeFormatter, for handling HTML form URL-encoded data
– System.Web.Http.ModelBinding.JQueryMvcFormUrlEncodedFormatter, for handling model-bound HTML form URL-encoded data
but I do not understand the difference!
I do not even use jquery to post my form:
<form role="form" method="post" action="api/values" enctype="application/x-www-form-urlencoded">
<input type="text" class="form-control" name="firstName" placeholder="Enter first name">
<input type="text" class="form-control" name="lastName" placeholder="Enter last name">
<button type="submit" class="btn btn-default">Submit</button>
</form>

Answer 1

FormUrlEncodedMediaTypeFormatter binds application/x-www-form-urlencoded body to FormDataCollection type, and only that type.
JQueryMvcFormUrlEncodedFormatter however uses available ModelBinders to first parse the body to FormDataCollection and then use the first compatible ModelBinder to parse that into the final model. It's like mixing Model Binding approach and Media Type Formatting approach, which AFAIK is not explained anywhere in the WebAPI docs.
Both formatters are registered by default. This is what I inferred reading WebAPI source code.

Answer 2

There are 4 out of box formatters
JsonMediaTypeFormatter
XMLMediaTypeFormatter
FormUrlEncodedMediaTypeFormatter
JQueryMvcFormUrlEncodedFormatter
The first two media type formatters can serialize and deserialize CLR types to request/response and vice versa. But 3rd one neither serializes nor deserializes to/from any CLR type. 4th formatter can deserialize incoming raw data to CLR type.
Hence in your case, you are experiencing with error after you remove JQueryMvcFormUrlEncodedFormatter since 3rd formatter could not able to deserialize incoming request data to CLR type.