Flutter: How to send packages as a tcp client

Question

I am trying to connect to the HHC-NET2D relay device.

This device allows connection to a tcp client. I have not found a solution with which I can send parameters to the device. If someone knows the recommended way to establish a connection through tcp client and send parameters it would be helpful.

Support
1. Support TCP Server, TCP client, UDP
2. Supporting 4 client connections in the TCP server. Assume that the local port is 5000. Port 5000 can be connected to the TCP client.
3. Support TCP MODBUS protocol.

Control command
5. Sent "on1" to the HHC-NET2D will turn on the First relay.
6. Sent "on2" to the HHC-NET2D will turn on the Second relay.
7. Sent "off1" to the HHC-NET2D will turn on the First relay.
8. Sent "off2" to the HHC-NET2D will turn on the Second relay.

Read more here: https://es.aliexpress.com/item/32358735415.html

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: HomeApp(),
    );
  }
}

class HomeApp extends StatefulWidget {
  @override
  _HomeAppState createState() => _HomeAppState();
}

class _HomeAppState extends State<HomeApp> {
  Socket socket;
  String name;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(name == null ? 'NO CONNECTED' : name),
      ),
      body: Container(
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text('Connect'),
              onPressed: (){
                connect();
              },
            ),
            RaisedButton(
              child: Text('Send Data'),
              onPressed: (){
                sendData();
              },
            )
          ],
        ),
      ),
    );
  }

  // Socket connection
  void connect() {
    Socket.connect("ipHere", portHere).then((Socket sock) {
      socket = sock;
      socket.listen(
          dataHandler,
          onError: errorHandler,
          onDone: doneHandler,
          cancelOnError: false
      );
    });
  }
  void dataHandler(data){
    setState(() {
      name = new String.fromCharCodes(data).trim();
    });
  }
  void errorHandler(error, StackTrace trace){
    print(error);
  }
  void doneHandler(){
    socket.destroy();
  }
  void sendData(){
    //socket.write(...)
  }
}

Solution

First create a string variable with the message you want to send.

And in your code update this:

socket.write(HERE_STRING_MESSAGE);