Bad state: Cannot set the body fields of a Request with content-type “application/json”

问题

Map<String,String> headers = {'Content-Type':'application/json','authorization':'Basic c3R1ZHlkb3RlOnN0dWR5ZG90ZTEyMw=='};

var response = await post(Urls.getToken,
        headers: headers,
        body: {"grant_type":"password","username":"******","password":"*****","scope":"offline_access"},
      );

When I execute this I am unable to recieve data and the error thrown is

Bad state: Cannot set the body fields of a Request with content-type "application/json"

回答1:

You need to wrap the body in jsonEncode.

import 'package:http/http.dart' as http;
import 'dart:convert';

Map<String,String> headers = {'Content-Type':'application/json','authorization':'Basic c3R1ZHlkb3RlOnN0dWR5ZG90ZTEyMw=='};
final msg = jsonEncode({"grant_type":"password","username":"******","password":"*****","scope":"offline_access"});

var response = await post(Urls.getToken,
               headers: headers,
               body: msg,
            );

回答2:

had similar issue with http library...changed for dio 2.1.0 and the problem with headers is gone.

jsonEncode(body) didn't do the trick, because the docs say:

Sends an HTTP POST request with the given headers and body to the given URL, which can be a [Uri] or a [String].

[body] sets the body of the request. It can be a [String], a [List] 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 [send] instead.

Future<Response> post(url, {Map<String, String> headers, body, Encoding encoding});

回答3:

Use jsonEncode to wrap your body object.

import 'package:http/http.dart' as http;
import 'dart:convert';

var headers = {
    'Content-Type':'application/json',
    'authorization':'Basic c3R1ZHlkb3RlOnN0dWR5ZG90ZTEyMw=='
};

final body = {
    'username':'foo',
    'password':'pass123'
}

var response = await post(
    Urls.getToken,
    headers: headers,
    body: jsonEncode(body), // use jsonEncode()
);

Why jsonEncode?

body: It can be a [String], a [List] or a [Map<String, 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".

but because you set the content-type to json you must have to pass a JSON as the body.

but you are passing Map<String, String> as the body, which obviously throws an error.

So to solve this issue you have to change or encode your Map<String, String> to json (JSON string) via using jsonEncode.

回答4:

Map<String,String> header = {'Content-Type':'application/json-patch+json','accept':'application/json'};
    final msg = jsonEncode({"username":"$emailorPhoneN","password":"$passwrod"});

    try {
      var response = await http.post(UrlConstants.loginUrl, headers: header, body: msg,
      ).timeout(Duration(seconds: httpDuration));
      var convert = json.decode(response.body);
      print('**********Data from server $convert');

      if (convert == null) {
        return null;
      } else {
        String token = convert['token'];

        if (token != null) {
          SignUpModel signUpModel = SignUpModel.fromJson(convert);
          return signUpModel;
        } else {
          //*** GET Error message from the API provider.....
          SignUpModel signUpModel = SignUpModel.fromJson(convert);
          return signUpModel;
        }
      }

来源：https://stackoverflow.com/questions/54849725/bad-state-cannot-set-the-body-fields-of-a-request-with-content-type-applicatio

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