Flutter循环内更新Json转Map的值不生效，疑为Bug

从REST API获取JSON数据后，通过jsonDecode生成List<Map<String,dynamic>>类型变量。在for循环内执行map['key'] = anyValue操作时，循环内打印显示值已修改，但循环结束后值又回滚至初始状态。我认为这是Flutter的Bug。

代码示例 #

"data": [
  {
    "id": 1,
    "title": "",
    "price": null,
    "some": [
      {
        "needToChange": 1 // int类型
      }
    ]
  }
]

List<dynamic> data = jsonDecode(res.body)['data'];
for(int i = 0 ; i < 10 ; i++){
  data['some']['needToChange'] = someArray[i]; // 赋值新的int值
  print(data['some']['needToChange']); // 当前显示已修改，但作用域结束后会回滚
}

print(data['some']['needToChange']); // 结果还是初始值1，没有变化

完整代码 #

dynamic res = await http.post(
  Uri.parse(C_URL_BASE + '/v1/post-query/abc'),
  headers: {
    "Content-Type": "application/json",
    "Accept": "application/json",
  },
  body: body
);

Map<String, dynamic> jsonData = json.decode(res.body);
List<dynamic> myList = [];
for (int i = 0; i < jsonData['data']['someA'].length; i++) {
  for (int k = 0; k < jsonData['data']['someB'].length; k++) {
    if (jsonData['data']['someA'][i]['nestedA'] ==
        jsonData['data']['someB'][k]['nestedB']) {
      var map = jsonData['data']['someB'][k];
      print(jsonData['data']['someA'][i]['id']);
      map.update('needToChange',
              (value) => jsonData['data']['someA'][i]['id']);
      myList.add(map);
    }
  }
}

print("it begins " + myList.length.toString());
for (int i = 0; i < myList.length; i++) {
  print(myList[i]['needToChange']); // 完全没变化！！
}

对应的JSON数据 #

"someA": [
  {
    "nestedA": 2,
    "id": 5
  },
  {
    "nestedA": 1,
    "id": 2
  },
  {
    "nestedA": 2,
    "id": 4
  },
  {
    "nestedA": 1,
    "id": 3
  },
  {
    "nestedA": 1,
    "id": 1
  }
],
"someB": [
  {
    "id": 1,
    "needToChange": 111
  }
]

内容的提问来源于stack exchange，提问作者dontknowhy