check_if_doc_exists

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: "AIzaSyA6H1jOIFt9e7V4h_CrlcGXzk0px36g_XM",
      authDomain: "gdg-community-app-c5120.firebaseapp.com",
      projectId: "gdg-community-app-c5120",
      storageBucket: "gdg-community-app-c5120.appspot.com",
      messagingSenderId: "884593610503",
      appId: "1:884593610503:web:436620635a564cc32e3fa2"
    )
  );

  runApp(HomeApp());
}

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

class HomePage extends StatelessWidget {
  
  @override
  Widget build(BuildContext context) {
    
    return Scaffold(
      body: StreamBuilder(
        stream: FirebaseFirestore.instance.collection('sample').doc('first').snapshots(),
        builder: (context, snapshot) {
          
          if (snapshot.hasData && (snapshot.data as DocumentSnapshot).exists) {
            Map<String, dynamic> docData = (snapshot.data as DocumentSnapshot).data() as Map<String, dynamic>;
            
            return Text(docData['value'].toString());
          }
          
          return Text('does not exist!');
        }
      )
    );
  }
}