没有为“ PinyinHelper”类定义“ convertToPinyinStringWithoutException”？

Question

有人可以帮助我解决未为类'PinyinHelper'定义错误'convertToPinyinStringWithoutException'的问题。扑扑中使用lpinyin的p2p消息服务代码：^ 1.0.8此依赖性，您还可以在以下链接https://github.com/Yidadaa/P2P-Message也使用较旧版本的android，但问题是它不允许我使用该功能？

    import 'dart:convert';
    import 'package:flutter/material.dart';
    import 'package:shared_preferences/shared_preferences.dart';
    import 'package:lpinyin/lpinyin.dart';
    import 'package:p2pmessage/utils/navigate.dart';
    import 'package:p2pmessage/utils/api.dart' as api;
    import 'package:p2pmessage/utils/time.dart' as time;

    import './components/avatar.dart';

    class ContactsPage extends StatefulWidget {
      ContactsPage({Key key}) : super(key: key);

      @override
      _ContactsPageState createState() => new _ContactsPageState();
    }

    class _ContactsPageState extends State<ContactsPage>
        with WidgetsBindingObserver {
      List<Map> friends = [];
      Map myProfile;

      Map<String, List<Map>> friendGroup = {};

      List<String> sortedKeys = [];

      void addFriend(Map f) {
        setState(() {
          // do something
        });
      }

      void loadContacts() async {
        if (myProfile == null) return;
        // 优先从本地数据库拉取数据
        List contacts = await api.collectContactFromDB();
        this.updateContact(contacts);
        // 然后从远程数据库拉取数据到本地
        contacts = await api.collectContacts(myProfile['id']);
        this.updateContact(contacts);
      }

      void updateContact(List contacts) {
        Map<String, List<Map>> newGroup = {};

        for (var f in contacts) {
          //*** THE ERROR IS OCCURING IN THE FOLLWING LINE ***
          var name = PinyinHelper.convertToPinyinStringWithoutException(f['name']);
          if (name.length > 0) {
            String superKey = name[0].toUpperCase();
            if (newGroup.containsKey(superKey)) {
              newGroup[superKey].add(f);
            } else {
              newGroup[superKey] = [f];
            }
          }
        }

        setState(() {
          friends = contacts;
          friendGroup = newGroup;
          sortedKeys = newGroup.keys.toList()..sort();
        });
      }

      List<Widget> _buildFriendGroup(String key, List<Map> fl) {
        return [
          new ListTile(
            leading: new DefaultTextStyle(
              style: new TextStyle(fontSize: 16.0, color: Colors.black),
              child: new Text(key),
            ),
          ),
        ]..addAll(fl.map((Map f) {
            return new InkWell(
              onTap: () {
                navigateTo(context, '/user', f);
              },
              child: new ListTile(
                leading: buildAvatar(f['avatar'], 50.0),
                title: new DefaultTextStyle(
                  style: new TextStyle(fontSize: 18.0, color: Colors.black),
                  child: new Text(f['name']),
                ),
                subtitle: new DefaultTextStyle(
                  style: new TextStyle(fontSize: 14.0, color: Colors.grey),
                  child: new Text(
                    f['status'] == 1
                    ? '当前在线'
                    : '上次在线' + time.format(f['last_online'] ?? new DateTime.now().millisecondsSinceEpoch)),
                ),
              ),
            );
          }).toList());
      }

      @override
      void initState() {
        super.initState();
        SharedPreferences.getInstance().then((prefs) {
          String userProfileStr = prefs.getString('user');
          if (userProfileStr == null) redirectTo(context, '/login', null);
          else {
            setState(() {
              Map userProfileJson = jsonDecode(userProfileStr);
              myProfile = userProfileJson;
            });
            this.loadContacts();
          }
        });
      }

      @override
      Widget build(BuildContext context) {
        List<Widget> lists = [];
        for (var key in sortedKeys) {
          lists.addAll(this._buildFriendGroup(key, friendGroup[key]));
        }
        return new Scaffold(
            body: new ListView(
              children: lists,
            ),
            floatingActionButton: new FloatingActionButton(
              onPressed: () {
                // Todo: 添加朋友
              },
              child: new Icon(Icons.add),
            ));
      }
    }