我在一个应用程序上使用API来获取用户信息，并在另一个选项卡中获取该特定用户的对话和消息线程，因为我知道我需要pid和tac（选项卡访问代码）作为参数，为了获取它们，它们位于另一个API（getTabAccessCode）的响应体中，我使用Postman尝试调用，它们工作正常。
下面是user_service.dart，在postman中，在其body响应中的getTabAccessCode函数中，我获得了User id，pid和tac（tab访问代码）：

static Future<Map<String, dynamic>> fetchUserInfo(String accessToken) async {
    final response = await http.get(
      Uri.parse(
          'https://example.app/auth/example/protocol/userinfo'),
      headers: {
        'Authorization': 'Bearer $accessToken',
      },
    );
    if (response.statusCode == 200) {
      return json.decode(response.body);
    } else {
      throw Exception(
          'Error fetching user information: ${response.statusCode}');
    }
  }
// This function takes a global ID and an access token as parameters
static Future<Map<String, dynamic>> getTabAccessCode(
  String globalId, String accessToken) async {
    // This is the URL for the device registration
    final tokenUrl =
        'http://example.com:9080/exp/rest/DeviceRegistration';
    // This is the HTTP GET request with the query parameters
    final response = await http.get(
      Uri.parse(
          '$tokenUrl?country=United%20Kingdom&emailID=example%40gmail.com&name=Patient%20Eleven&zoneinfo=Europe%2FParis&GlobalId=$globalId&postal_code=70001&gender=Female&accesstoken=$accessToken&appname=example'),
    );
    
    // This checks if the response status code is 200, which means OK
    if (response.statusCode == 200) {
      // This parses the response body into a Dart object
      final responseBody = jsonDecode(response.body);
      // Print the entire response line
      print('Response: $responseBody');
      // This gets the value of "TabAccCode"
      final tabAccessCode = responseBody["TabAccCode"];
      // If the response includes "pid" and "doctor id", retrieve them as well
      final pid = responseBody["pid"];
      final doctorid = responseBody["doctorid"];
      // Create a map to return all the values
      final resultMap = {
        "tabAccessCode": tabAccessCode,
        "pid": pid,
        "doctorid": doctorid,
      };
      // This returns the map containing all the values
      return resultMap;
    } else {
      // This throws an exception if the response status code is not 200
      throw Exception('Error getting Tab Access Info: ${response.statusCode}');
    }
  }

注意：getTabAccessCode API调用的响应中tab访问代码的名称为TabAccCode，而在会话和消息API调用的参数中则称为tac。
有人能帮助我吗？我是一个使用API的新手，我被困在这里了。
这是conversation_page.dart，下面我试图调用函数（getTabAccessCode)，它的响应中有pid和tac，但它说globalid和accesstoken是未定义的，因为它们已经定义了，但在user_service.dart中：

import 'dart:convert';
import 'package:efindadoc/screens/messages_page.dart';
import 'package:efindadoc/screens/user_service.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
class ConversationPage extends StatefulWidget {
  @override
  _ConversationPageState createState() => _ConversationPageState();
}
class _ConversationPageState extends State<ConversationPage> {
  List<Map<String, dynamic>> conversations = [];
  String pid = '';
  String tac = '';
  @override
  void initState() {
    super.initState();
    initConversations();
  }
  Future<void> initConversations() async {
    var accessInfo = await UserService.getTabAccessCode(globalId, accessToken);
    var pid = accessInfo["pid"];
    var tac = accessInfo["tabAccessCode"];
    await fetchConversations(pid, tac);
  }
  Future<void> fetchConversations(String pid, String tac) async {
    final response = await http.get(Uri.parse(
      'https://example.com/docs/getMessages?pid=$pid&user_type=doctor&function=conversation&tac=$tac&view_as=doctor',
    ));
    if (response.statusCode == 200) {
      final data = jsonDecode(response.body);
      if (data['success']) {
        final List<dynamic> conversationData = data['data'];
        conversations = conversationData
            .map((conversation) => Map<String, dynamic>.from(conversation))
            .toList();
      }
    } else {
      throw Exception('Failed to load conversation data');
    }
    setState(() {});
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Conversation Page'),
      ),
      body: ListView.builder(
        itemCount: conversations.length,
        itemBuilder: (context, index) {
          final conversation = conversations[index];
          return ListTile(
            title: Text(conversation['title']),
            subtitle: Text(conversation['created']),
            onTap: () {
              Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) => MessagePage(
                      conversationId: conversation['id'], pid: pid, tac: tac),
                ),
              );
            },
          );
        },
      ),
    );
  }
}

这是messages_page.dart：

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
class MessagePage extends StatefulWidget {
  final String conversationId;
 
 
  final String pid;
  final String tac;
  MessagePage({required this.conversationId, required this.pid, required this.tac});
  @override
  _MessagePageState createState() => _MessagePageState();
}
class _MessagePageState extends State<MessagePage> {
  List<Map<String, dynamic>> messages = [];
  @override
  void initState() {
    super.initState();
    fetchMessages();
  }
Future<void> fetchMessages() async {
  final response = await http.get(Uri.parse(
    'https://example.com/doc/getMessages?user_type=doctor&function=messages&conversation_id=${widget.conversationId}&pid=$pid&tac=$tac&view_as=doctor',
  ));
    if (response.statusCode == 200) {
      final data = jsonDecode(response.body);
      if (data['success']) {
        final List<dynamic> messagesData = data['data']['messages'];
        messages = messagesData.map((message) => Map<String, dynamic>.from(message)).toList();
      }
    } else {
      throw Exception('Failed to load messages data');
    }
    setState(() {});
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Message Page'),
      ),
      body: ListView.builder(
        itemCount: messages.length,
        itemBuilder: (context, index) {
          final message = messages[index];
          return ListTile(
            title: Text(message['sender_name']),
            subtitle: Text(message['message']),
            // You can customize how you want to display the message data here.
            // For example, you can format the sent_at date, display sender's type, etc.
          );
        },
      ),
    );
  }
}