我检查了request.send的文档，返回了Future<StreamedResponse>而不是Future<Response>
深入挖掘StreamedResponse，我发现它是response.stream，也就是ByteStream
下面是可以用String格式获得响应的方法

final response = await request.send();
final respStr = await response.stream.bytesToString();

在我看来，如果你想要流式响应而不是“收集”响应，你应该只使用request.send。

只需使用http.Response.fromStream()

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

var streamedResponse = await request.send()
var response = await http.Response.fromStream(streamedResponse);

你可以在第一次回应后投，看：

var postUri = Uri.parse("http://my-api.com/updatePhoto");
var request = new http.MultipartRequest("POST", postUri);

request.fields['user_id'] = user_id

request.files.add(await http.MultipartFile.fromPath(
  'photo',
  myPhoto.absolute.path,
  contentType: new MediaType('application', 'x-tar'),
));

request.send().then((result) async {

  http.Response.fromStream(result)
      .then((response) {

    if (response.statusCode == 200)
    {
      print("Uploaded! ");
      print('response.body '+response.body);
    }

    return response.body;

  });
}).catchError((err) => print('error : '+err.toString()))
    .whenComplete(()
{});

这就是我期望的json对象：

{"hasErrors":true,"errorMessage":"Some Error Message","done":false}

基于“hasErrors”属性，我想执行一些操作。
这是我如何从Http Post请求获得它：

var request = http.Request('POST', url);
  request.body = json.encode(data);
  request.headers.addAll(headers);

  var streamedResponse = await request.send();
  var response = await http.Response.fromStream(streamedResponse);
  final result = jsonDecode(response.body) as Map<String, dynamic>;
  return !result['hasErrors'];

由于使用了request.send，MultipartRequest返回了Streamed Response。您需要从响应中提取字符串值，如下所示：

import 'package:http/http.dart'

var request = new MultipartRequest("POST", uri);
var response = await request.send()

// Extract String from Streamed Response
var responseString = await response.stream.bytesToString();

在这种情况下，responseString将类似于

final response = await post(URL, body : map);

import 'package:http/http.dart'
    import 'dart:convert';
    
    var request = new MultipartRequest("POST", uri);
    var response = await request.send()
    
    // Extract String from Streamed Response
    var responseString = await response.stream.bytesToString();
    final decodedMap = json.decode(responseString);
    print(decodedMap['id']);
    print(decodedMap['name']);

对我有效的是，

await res.stream.transform(utf8.decoder).transform(json.decoder).first;

在下面的例子中，我对响应于我的模型类（UserModel）的流进行解码

var streamedResponse = await request.send();
        var response = await http.Response.fromStream(streamedResponse);
        if (response.statusCode == 200) {
          var parsed = jsonDecode(response.body);
          UserModel userModel= UserModel.fromJson(parsed);
          return userModel;
}
else{
print(error);
}