问如何在Flutter中使用http.post并作为String Json对象发送

EN

I / flutter(28184): 200
I / flutter(28184): {"error": "the JSON object must be str, not 'bytes'"}

Future<http.Response> sendPost() async{
    var post = {
      "profile_id" : "${_profile_id}",
      "profile_name" : "${_profile_Name}",
      "profile_country" : "${_profile_country}",
      "post_id" : "${current_post_id}",
      "post_image_id" : "${current_post_image}",
      "post_desc" : "La La La La La La",
      "post_likes" : "${post_likes}",
      "post_timestamp" : "05-06-2019 22:34",
      "post_comments" : [],
      "post_comments_profile_name" : [],
      "post_comments_profile_image_id" : [],
      "post_comments_timestamp" : []
    };


    var body = utf8.encode(json.encode(post));

    var addPost = await http.post(
      url,
      headers: {"content-type" : "application/json"},
      body: body

      );

      print("${addPost.statusCode}");
      print("${addPost.body}");
      return addPost;
  }