Flutter HTTP Post returns 415 - dart

Question

I have an issue with using Method.Post on my flutter app using http dart library. It seems that when I tried to post data from my WebAPI it gaves me a StatusCode 415. See my code below:
Code Login:
Future<User> login(User user) async {
print(URLRequest.URL_LOGIN);
return await _netUtil.post(Uri.encodeFull(URLRequest.URL_LOGIN), body: {
'username': user.username,
'password': user.password
}, headers: {
"Accept": "application/json",
}).then((dynamic res) {
print(res.toString());
});
}
Code NetworkUtils:
Future<dynamic> post(String url, {Map headers, body, encoding}) async {
return await http
.post(url, body: body, headers: headers, encoding: encoding)
.then((http.Response response) {
final String res = response.body;
final int statusCode = response.statusCode;
if (statusCode < 200 || statusCode > 400 || json == null) {
throw new Exception('Error while fetching data.');
}
return _decoder.convert(res);
});
}
Does anyone knew whats going on my code?

Answer 1

Try adding this new header:
headers: {
"Accept": "application/json",
"content-type":"application/json"
}
UPDATE
Ok now you need to send json data, like this :
import 'dart:convert';
var body = jsonEncode( {
'username': user.username,
'password': user.password
});
return await _netUtil.post(Uri.encodeFull(URLRequest.URL_LOGIN), body: body, headers: {
"Accept": "application/json",
"content-type": "application/json"
}).then((dynamic res) {
print(res.toString());
});
}

Answer 2

#Alvin Quezon
I met the same error as yours and fix it, please see below.
[Error]
StateError (Bad state: Cannot set the body fields of a Request with content-type "application/json".)
[Reason]
when you use the Flutter plug 'http.dart' method 'http.post()', you should read the document in detail below (note the black fonts):
Sends an HTTP POST request with the given headers and body to the given URL.
[body] sets the body of the request. It can be a [String], a [List<int>] or
a [Map<String, String>]. If it's a String, it's encoded using [encoding] and
used as the body of the request. The content-type of the request will
default to "text/plain".
If [body] is a List, it's used as a list of bytes for the body of the
request.
If [body] is a Map, it's encoded as form fields using [encoding]. The content-type of the request will be set to "application/x-www-form-urlencoded"; this cannot be overridden.
[encoding] defaults to [utf8].
For more fine-grained control over the request, use [Request] or
[StreamedRequest] instead.
Future<Response> post(Uri url,
{Map<String, String>? headers, Object? body, Encoding? encoding}) =>
_withClient((client) =>
client.post(url, headers: headers, body: body, encoding: encoding));
[Solution]
So just encode your body as a string ,then you can set the header 'content-type' as 'application/json'.
see the codes of #diegoveloper answered!