无法加载源'dart：core / runtime / libobject_patch.dart'：<source not =“” available =“” />

Question

我收到此错误：

  

无法加载源'dart：core / runtime / libobject_patch.dart'：<源不可用\>

Project on GitHub

我有两个下拉列表（一个带有体育项目的下拉列表，另一个带有国家的列表）和一个联赛列表。在下拉列表中选择项目时，应该对带有联赛的列表进行排序。当我在下拉列表中选择城市时，会弹出此错误。

Future<List<ListTile>> _getListLeagues() async {
    http.Response data;
    String _str = "countrys";
    List<ListTile> listTiles = [];

    if ((_choiseCountry == null) & (_choisesport == null)) {
      data = await http
          .get("https://www.thesportsdb.com/api/v1/json/1/all_leagues.php");
      _str = "leagues";
    } else if ((_choisesport != null) & (_choiseCountry == null)) {
      data = await http.get(
          "https://www.thesportsdb.com/api/v1/json/1/search_all_leagues.php?s=$_choisesport");
    } else if ((_choiseCountry != null) & (_choisesport == null)) {
      data = await http.get(
          "https://www.thesportsdb.com/api/v1/json/1/search_all_leagues.php?c=$_choiseCountry");
    } else {
      data = await http.get(
          "https://www.thesportsdb.com/api/v1/json/1/search_all_leagues.php?c=$_choiseCountry&s=$_choisesport");
    }

    var jsonData = json.decode(data.body);

    for (var index in jsonData[_str]) {
      if (((_choisesport != null) & (_choisesport == index["strSport"])) |
          (_choisesport == null)) {
        ListTile list = ListTile(
          title: Text(index["strLeague"]),
          subtitle: Text(index["strSport"]),
        );
        listTiles.add(list);
      }
    }
    return listTiles;
  }
}

Future<List<DropdownMenuItem<String>>> _sports() async {
  var data = await http
      .get("https://www.thesportsdb.com/api/v1/json/1/all_sports.php");
  var jsonData = json.decode(data.body);

  List<DropdownMenuItem<String>> droplist = [];

  for (var sport in jsonData["sports"]) {
    droplist.add(DropdownMenuItem(
      child: Row(children: <Widget>[
        Text(sport["strSport"].toString()),
      ]),
      value: sport["strSport"],
    ));
  }
  return droplist;
}