发送帖子请求时参数无效

Question

我这里有一些json对象-

{
    "error": "0",
    "message": "Got it!",
    "data": [
        {
            "status": "false",
            "_id": "5e3cf1deda2fb4000751d2a2",
            "group_id": "5e37ff5172828bad9806386e",
            "date": "2020-02-06T00:00:00.000Z",
            "title": "brand",
            "priority": 3,
            "description": ""
        },
        {
            "status": "false",
            "_id": "5e3bc849640e57000821bd60",
            "group_id": "5e37ff9872828b1ed806386f",
            "date": "2020-02-05T00:00:00.000Z",
            "title": "new task",
            "priority": 4,
            "description": ""
        },
        {
            "status": "false",
            "_id": "5e37c578a9678c2863bbb4e8",
            "title": "making task with true status 1",
            "date": "2020-02-03T00:00:00.000Z",
            "group_id": "5df8aaae2f85481f6e31db59",
            "priority": 1,
            "description": "some description"
        },
        {
            "status": "false",
            "_id": "5e37c9524c05b6f1560d9d9e",
            "group_id": "5e35214f89e915437c2a9705",
            "date": "2020-02-02T00:00:00.000Z",
            "title": " h h h ",
            "priority": 4,
            "description": ""
        }
    ],
    "total_count": 4,
    "skip": 0
}

我正在尝试将此数据获取到日历小部件（使用此插件-https://pub.dev/packages/table_calendar）。但我一直收到此错误-

[ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: Invalid argument(s)

有一个地图和一个显示UI的列表-该地图允许日历显示具有相应“ date”参数的任何json对象，并以此方式在UI中进行反映（顶部带有点的日期带有一个json对象的“日期”参数映射到“标题”参数）

API还具有一个请求正文-“年”和“月”。年和月参数必须在日历中具有当前显示的年和月。

Calendar UI

该列表应该在列表视图中显示所有具有相同“ date”参数的json对象。我能够显示获取并将数据显示到地图，但是当我尝试将数据获取到列表时，出现上述错误。

发布请求以获取地图-

  Map<DateTime, List> _events;


// inside initstate

getTask().then((val) => setState(() {
_events = val;  // _events is the map
print("PRINTING EVENTS = $_events");
print("PRINTING EVENTSval = $val");

}));

 returnMonth(){ // using this method since the plugin returns an integer for the currently displayed month whereas The api requires a string with the name of month.

    if(_calendarController.selectedDay.month == 1){
      return "january";
    }else

    if(_calendarController.selectedDay.month == 2){
      return "february";
    }else
    if(_calendarController.selectedDay.month == 3){
      return "march";
    }else
    if(_calendarController.selectedDay.month == 4){
      return "april";
    }else
    if(_calendarController.selectedDay.month == 5){
      return "may";
    }else
    if(_calendarController.selectedDay.month == 6){
      return "june";
    }else
    if(_calendarController.selectedDay.month == 7){
      return "july";
    }else
    if(_calendarController.selectedDay.month == 8){
      return "august";
    }else
    if(_calendarController.selectedDay.month == 9){
      return "september";
    }else
    if(_calendarController.selectedDay.month == 10){
      return "october";
    }else
    if(_calendarController.selectedDay.month == 11){
      return "november";
    }else
    if(_calendarController.selectedDay.month == 12){
      return "december";
    }
  }

// outside initstate

  Future<Map<DateTime, List>> getTask() async {
    Map<DateTime, List> mapFetch = {};

    await Future.delayed(const Duration(seconds: 1), () {});


    String link = fetchTodoInCalendarUrl;
    var res = await http.post(link, headers: {"Accept": "application/json"}, body: {"month": returnMonth(), "year" : jsonEncode(_calendarController.selectedDay.year)});
    if (res.statusCode == 200) {
        Welcome event = welcomeFromJson(res.body);
    }

    Welcome event =welcomeFromJson(res.body);
setState(() {
  for (int i = 0; i < event.data.length; i++) {
    mapFetch[event.data[i].date] = [event.data[i].title];

  }
});
    return mapFetch;
  }

发布列表请求-

  List _selectedEvents;

// inside initstate

    getTaskPractice().then((val) => setState(() {
  _selectedEvents = val;
  print("PRINTING SELECTED EVENTS = $_selectedEvents");
  print("PRINTING EVENTSval = $val");

}));

// outside initstate


  Future<List> getTaskPractice() async {
    List mapFetch = [];

    await Future.delayed(const Duration(seconds: 1), () {});

    String link = fetchTodoInCalendarUrl;
    var res = await http.post(link, headers: {"Accept": "application/json", "Content-Type":  "application/x-www-form-urlencoded"}, body: {"month" : returnMonth(), "year" : jsonEncode(_calendarController.selectedDay.year)});
    if (res.statusCode == 200) {
      var data = json.decode(res.body);
      var rest = data['data'];
      var error = data['error'];
      print("this is error = $error");
//    print("PrintingREST = $rest");

      print("PRINTING REST FOR TASKPRACTICE= $rest");
      print("PRINTING RESBODY FOR TASK PRACTICE= ${res.body}");

      final demoJsonMapEntries = rest.map((data) {
        return MapEntry(DateTime.parse(data['date']), data['title']);
      });

      print("PRINTING DEMOJSONMAPENTRIES = $demoJsonMapEntries");

      demoJsonMapEntries.forEach((e) {
        // Normalize the `date` - this is necessary to ensure proper `Map` behavior
        final key = DateTime.utc(e.key.year, e.key.month, e.key.day, 12);

        _events.update(key, (list) => list..add(e.value), ifAbsent: () => [e.value]);

        DatumCalendar event = welcomeFromJsonDatumCalendar(res.body);
//        for (int i = 0; i < res.body.length; i++) {
//          mapFetch[event.date][i] = [event.title][i];  // tried to do this but since event.date is a datetime, this statement returns an error
//
//        }

      });
    }

    Welcome event = welcomeFromJson(res.body);
    setState(() {
//      for (int i = 0; i < event.data.length; i++) {
//        mapFetch[event.data[i].date.toString()] = [event.data[i].title];
//
//      }

    });
    return mapFetch;
  }

json模型=

Welcome welcomeFromJson(String str) => Welcome.fromJson(json.decode(str));

//String welcomeToJson(Welcome data) => json.encode(data.toJson());

class Welcome {
  dynamic error;
  dynamic message;
  List<DatumCalendar> data;
  dynamic totalCount;
  dynamic skip;

  Welcome({
    this.error,
    this.message,
    this.data,
    this.totalCount,
    this.skip,
  });

  factory Welcome.fromJson(Map<String, dynamic> json) => Welcome(
    error: json["error"],
    message: json["message"],
    data: List<DatumCalendar>.from(json["data"].map((x) => DatumCalendar.fromJson(x))),
    totalCount: json["total_count"],
    skip: json["skip"],
  );

  Map<String, dynamic> toJson() => {
    "error": error,
    "message": message,
    "data": List<dynamic>.from(data.map((x) => x.toJson())),
    "total_count": totalCount,
    "skip": skip,
  };
}

DatumCalendar welcomeFromJsonDatumCalendar(String str) => DatumCalendar.fromJson(json.decode(str));


class DatumCalendar {
  dynamic status;
  dynamic  id;
  dynamic   groupId;
  DateTime date;
  dynamic   title;
  dynamic    priority;
  dynamic   description;

  DatumCalendar({
    this.status,
    this.id,
    this.groupId,
    this.date,
    this.title,
    this.priority,
    this.description,
  });

  factory DatumCalendar.fromJson(Map<String, dynamic> json) => DatumCalendar(
    status: json["status"],
    id: json["_id"],
    groupId: json["group_id"],
    date: DateTime.parse(json["date"]),
    title: json["title"],
    priority: json["priority"],
    description: json["description"],
  );

  Map<String, dynamic> toJson() => {
    "status": status,
    "_id": id,
    "group_id": groupId,
    "date": date.toUtc(),
    "title": title,
    "priority": priority,
    "description": description,
  };
}

由于发布请求似乎适用于地图而不是列表，因此我对我要去的地方感到困惑。我可以就如何正确实施此方法获得一些建议吗？