Implementing WebSocket in a StatefulWidget

chat.screen.dart

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

class ChatScreen extends StatefulWidget {
  @override
  _ChatScreenState createState() => _ChatScreenState();
}

class _ChatScreenState extends State<ChatScreen> {
  final channel = WebSocketChannel.connect(
    Uri.parse('wss://echo.websocket.org'),
  );
  final TextEditingController controller = TextEditingController();
  String lastMessage = "";

  void sendMessage() {
    if (controller.text.isNotEmpty) {
      channel.sink.add(controller.text);
      controller.clear();
    }
  }

  @override
  void initState() {
    super.initState();
    channel.stream.listen((message) {
      setState(() {
        lastMessage = message;
      });
    });
  }

  @override
  void dispose() {
    channel.sink.close();
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("WebSocket Chat")),
      body: Padding(
        padding: EdgeInsets.all(20),
        child: Column(
          children: [
            Text("Último mensaje: $lastMessage"),
            TextField(
              controller: controller,
              decoration: InputDecoration(labelText: "Escribe un mensaje"),
            ),
            ElevatedButton(onPressed: sendMessage, child: Text("Enviar")),
          ],
        ),
      ),
    );
  }
}