如何显示当前正在发言的用户的图像，Flutter Agora agora_rtc_engine？

import 'package:flutter/material.dart';
import 'package:agora_rtc_engine/agora_rtc_engine.dart';

class AgoraVideoChat extends StatefulWidget {
  @override
  _AgoraVideoChatState createState() => _AgoraVideoChatState();
}

class _AgoraVideoChatState extends State<AgoraVideoChat> {
  final _users = <int>[];
  final _infoStrings = <String>[];
  bool _isInChannel = false;

  @override
  void initState() {
    super.initState();
    initializeAgora();
  }

  Future<void> initializeAgora() async {
    await AgoraRtcEngine.create('YOUR_APP_ID');
    AgoraRtcEngine.onUserJoined = (int uid, int elapsed) {
      setState(() {
        _users.add(uid);
      });
    };
    AgoraRtcEngine.onUserOffline = (int uid, int reason) {
      setState(() {
        _users.remove(uid);
      });
    };
    AgoraRtcEngine.enableVideo();
    AgoraRtcEngine.joinChannel(null, 'YOUR_CHANNEL_NAME', null, 0);
    setState(() {
      _isInChannel = true;
    });
  }

  @override
  void dispose() {
    AgoraRtcEngine.leaveChannel();
    AgoraRtcEngine.destroy();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Agora Video Chat'),
      ),
      body: Center(
        child: _isInChannel
            ? Stack(
                children: [
                  _viewRows(),
                  _toolbar(),
                ],
              )
            : Text('Joining channel...'),
      ),
    );
  }

  Widget _viewRows() {
    final views = _users.map<Widget>((uid) => _videoView(uid)).toList();
    return Container(
      child: views.length > 1
          ? Row(
              children: views,
            )
          : views[0],
    );
  }

  Widget _videoView(int uid) {
    final viewId = AgoraRtcEngine.createNativeView(uid.toString());
    AgoraRtcEngine.setupRemoteVideo(viewId, VideoRenderMode.Hidden);
    AgoraRtcEngine.startRemoteVideo(uid);
    return Expanded(
      child: Container(
        child: AgoraRtcEngine.buildNativeView(viewId),
      ),
    );
  }

  Widget _toolbar() {
    return Container(
      alignment: Alignment.bottomCenter,
      padding: const EdgeInsets.symmetric(vertical: 48),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          RawMaterialButton(
            onPressed: () {},
            child: Icon(
              Icons.call_end,
              color: Colors.white,
              size: 20.0,
            ),
            shape: CircleBorder(),
            elevation: 2.0,
            fillColor: Colors.redAccent,
            padding: const EdgeInsets.all(12.0),
          ),
        ],
      ),
    );
  }
}