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我正在尝试在Dart中编写一个小命令行库来使用Facebook API.我有一个类'fbuser',它获取auth-token和user-id作为属性,并且有一个方法'groupIds',它应该返回一个List,其中包含来自用户的所有组ID.

当我调用该方法时,它返回null,尽管在http响应之后调用了两个可能的返回.我做错了什么？

这是我的代码:

import 'dart:convert'; //used to convert json 
import 'package:http/http.dart' as http; //for the http requests

//config
final fbBaseUri = "https://graph.facebook.com/v2.1";
final fbAppID = "XXX";
final fbAppSecret = "XXY";

class fbuser {
  int fbid;
  String accessToken;

  fbuser(this.fbid, this.accessToken); //constructor for the object

  groupIds(){ //method to get a list of group IDs
    var url = "$fbBaseUri/me/groups?access_token=$accessToken"; //URL for the API request
    http.get(url).then((response) {
      //once the response is here either process it or return an error
      print ('response received');
      if …