File upload to server Using dio And http

f.dart

///////////////////////////////////////////////////DIO//////////////////////////////////////
////////////////HEADERs
    dio.options.headers = {'Content-Type': 'application/x-www-form-urlencoded'};
      //code
 File _image;
String fileName =
                                                  _image.path.split('/').last;
       FormData formData =
                                                  new FormData.fromMap({
                                              
                                                'image': await MultipartFile
                                                    .fromFile(
                                                  _image.path,
                                                  filename: fileName,
                                                )
                                              });
                                           
                                           var results =   await provider
                                                  .upload(formData);
   
////////////////////////////////////////////////////HTTP

Future<String> uploadImageHTTP(file, url) async {

  var request = http.MultipartRequest('POST', Uri.parse(url));
  request.files.add(await http.MultipartFile.fromPath('picture', file.path));
  var res = await request.send();
  return res.reasonPhrase;

}