How to handle complex API data response in Flutter GetX using observable method

item_model.dart

class ItemModel {  int id;  String description;  String amount;  String type;  int userId;  DateTime createdAt;  DateTime updatedAt;  ItemModel.fromJson(Map<String, dynamic> data) {    id = data['id'];    description = data['description'];    amount = data['amount'];    type = data['type'];    userId = data['userId'];    if (data['created_at'] != null) createdAt = DateTime.parse(data['created_at']);    if (data['updated_at'] != null) updatedAt = DateTime.parse(data['updated_at']);  }}

page_links_model.dart

class PageLinksModel {  String first, last, prev, next;  PageLinksModel.fromJson(Map<String, dynamic> data) {    first = data['first'];    last = data['last'];    prev = data['prev'];    next = data['next'];  }}

pages_status_model.dart

class PagesStatusModel {  int currentPage, from, lastPage;  var links = List<PageInfoModel>();  String path;  int perPage, to, total;  PagesStatusModel.fromJson(Map<String, dynamic> data) {    currentPage = data['current_page'];    from = data['from'];    lastPage = data['last_page'];    (data['links'] as List).forEach((e) => links.add(PageInfoModel.fromJson(e)));    path = data['path'];    perPage = data['per_page'];    to = data['to'];    total = data['total'];  }}class PageInfoModel {  String url;   dynamic label;  bool active;  PageInfoModel.fromJson(Map<String, dynamic> data) {    url = data['url'];    label = data['label'];    active = data['active'];  }}

transaction_model.dart

import 'package:getx_api/models/pages_status_model.dart';class TransactionModel {  var data = List<ItemModel>();  PageLinksModel links;  PagesStatusModel meta;  TransactionModel.fromJson(Map<String, dynamic> source) {    (source['data'] as List).forEach((e) => data.add(ItemModel.fromJson(e)));    links = PageLinksModel.fromJson(source['links']);    meta = PagesStatusModel.fromJson(source['meta']);  }}

net_service.dart

import 'dart:convert';import 'package:getx_api/src/shared/transactions_data.dart';import 'package:http/http.dart' as http;class NetService {  static Future fetchJsonData(String url) {    return      http.get(url)        .then((response) => response?.statusCode == 200 ? jsonDecode(response.body) : null)        .catchError((err) => print(err));  }  static Future fetchLocalJsonData() async {    await Future.delayed(Duration(seconds: 3));    return jsonDecode(transactionData) as Map<String, dynamic>;  }}

transaction_controller.dart

import 'package:get/get.dart';import 'package:getx_api/models/transaction_model.dart';import 'package:getx_api/services/net_service.dart';const _serverUrl = 'http://10.0.2.2:8000/api/transactions';class TransactionController extends GetxController {  var _trx;  var _dataAvailable = false.obs;  @override  void onInit() {    super.onInit();    fetchTransactions();  }  bool get dataAvailable => _dataAvailable.value;  TransactionModel get trx => _trx;  Future<void> fetchTransactions() {    // return NetService.fetchJsonData(_serverUrl)    return NetService.fetchLocalJsonData()      .then((response) {        if (response != null) _trx = TransactionModel.fromJson(response);      })      .catchError((err) => print('Error!!!!! : $err'))      .whenComplete(() => _dataAvailable.value = _trx != null);  }}

home_page.dart

import 'package:flutter/material.dart';import 'package:get/get.dart';import 'package:getx_api/src/controllers/transaction_controller.dart';class HomePage extends StatelessWidget {  /* ---------------------------------------------------------------------------- */  const HomePage({Key key}) : super(key: key);  /* ---------------------------------------------------------------------------- */  @override  Widget build(BuildContext context) {    final obj = Get.put(TransactionController());    return Scaffold(      appBar: buildAppBar(),      body: Obx(() => obj.dataAvailable        ? Text(obj.trx.toString())        : Text('... waiting ...')),    );  }  /* ---------------------------------------------------------------------------- */  AppBar buildAppBar() {    return AppBar(      title: Text('Hi!'),      centerTitle: true,    );  }}

transactions_data.dart

const transactionData = '''{    "data": [    ....    }}''';