firebase_send_msg_to_user

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:cloud_firestore/cloud_firestore.dart';


void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  
  await Firebase.initializeApp(
    options: const FirebaseOptions(
      apiKey: "AIzaSyDOdBmVvI30Jg49oup4gsJMZMjTPhHOloQ",
      authDomain: "fullstack-labs.firebaseapp.com",
      databaseURL: "https://fullstack-labs.firebaseio.com",
      projectId: "fullstack-labs",
      storageBucket: "fullstack-labs.appspot.com",
      messagingSenderId: "251418261584",
      appId: "1:251418261584:web:2e01357a093d27476b7955"
    )
  );

  runApp(MessageApp());
}

class MessageApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        textTheme: GoogleFonts.poppinsTextTheme(
          Theme.of(context).textTheme
        )
      ),
      home: MessageWidget()
    );
  }
}

class MessageWidget extends StatelessWidget {
  
  String documentId = 'user1';
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            Text(documentId.toUpperCase(), style: const TextStyle(color: Colors.blue, fontSize: 20)),
            StreamBuilder(
              stream: FirebaseFirestore.instance.collection('users').doc(documentId).snapshots(),
              builder: (context, snapshot) {
                
                var message = '--No message--';
                
                if (snapshot.hasData) {
                  var messageDoc = (snapshot.data as DocumentSnapshot).data() as Map<String, dynamic>;
                  message = messageDoc['message'];
                }
                
                return Text(message);
              }
            ),
            TextButton(
              onPressed: () {
                FirebaseFirestore.instance.collection('users').doc(documentId).update({
                  'message': 'New Message sent ' + DateTime.now().toString()
                });
              },
              child: Text("Click me to send Message to " + documentId)
            )
          ]
        )
      )
    );
  }
}