added provider to listen firebase changes

Author: konstantinPopovskikh

README.md

@@ -8,5 +8,5 @@ This app is used to test the following features:
 - ```Clean DB``` - removes all tables from SQLite database and creates them again;
 - ```Old Json Caching Example``` - fetching data from REST API and caching into SQLite;
 
-- Firebase notifications are also enabled. FCM token is shown in debug console at startup. Copy the token and go to "Cloud messaging" in Firebase console to test in out.
+- Firebase notifications are also enabled. FCM token is shown in debug console at startup. Copy the token and go to "Cloud messaging" in Firebase console to test it out.
 

lib/backend/firestore_changes.dart

@@ -0,0 +1,25 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:flutter/foundation.dart';
+
+class FirestoreChanges extends ChangeNotifier {
+  String changeStr = '';
+
+  void listenOnFirestoreChanges() {
+    FirebaseFirestore.instance
+        .collection('flutter-caching')
+        .snapshots()
+        .listen((event) {
+      changeStr = '';
+      for (var change in event.docChanges) {
+        // print('Change type: ${change.type}; Data: '
+        //     '${change.doc.data()}\n');
+        changeStr = changeStr +
+            'Change type: ${change.type};\n'
+                'Doc ID: ${change.doc.id}\n'
+                'Data: ${change.doc.data()}\n';
+      }
+      notifyListeners();
+      // changeStr = '';
+    });
+  }
+}

lib/main.dart

@@ -1,3 +1,4 @@
+import 'package:fetchingapp/backend/firestore_changes.dart';
 import 'package:fetchingapp/backend/notifications.dart';
 import 'package:fetchingapp/screens/home.dart';
 import 'package:fetchingapp/screens/login.dart';
@@ -13,6 +14,7 @@ Future<void> main() async {
   await Firebase.initializeApp();
 
   initializeMessaging();
+  // listenOnFirestoreChanges();
 
   var token = await FirebaseMessaging.instance.getToken();
   print('FCM token: $token');
@@ -49,11 +51,16 @@ class _MyAppState extends State<MyApp> {
       firstScreen = const LoginPage();
     }
 
-    return MaterialApp(
-      theme: ThemeData(
-        primarySwatch: Colors.blue,
+    
+
+    return ChangeNotifierProvider(
+      create: (_) => FirestoreChanges(),
+      child: MaterialApp(
+        theme: ThemeData(
+          primarySwatch: Colors.blue,
+        ),
+        home: firstScreen,
       ),
-      home: firstScreen,
     );
   }
 }

lib/screens/home.dart

@@ -1,4 +1,5 @@
 import 'package:fetchingapp/backend/database.dart';
+import 'package:fetchingapp/backend/firestore_changes.dart';
 import 'package:fetchingapp/backend/google_authentication.dart';
 import 'package:fetchingapp/screens/firestore_stream.dart';
 import 'package:fetchingapp/screens/firestore_future.dart';
@@ -7,6 +8,7 @@ import 'package:fetchingapp/screens/login.dart';
 import 'package:fetchingapp/screens/provider_test.dart';
 import 'package:firebase_auth/firebase_auth.dart';
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 
 class HomePage extends StatelessWidget {
   const HomePage(this.user, {Key? key}) : super(key: key);
@@ -15,6 +17,9 @@ class HomePage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    Provider.of<FirestoreChanges>(context, listen: false)
+        .listenOnFirestoreChanges();
+
     return Scaffold(
       appBar: AppBar(
         automaticallyImplyLeading: false,
@@ -27,7 +32,7 @@ class HomePage extends StatelessWidget {
           const SizedBox(height: 10),
           testSectionButton(
               context: context,
-              name: 'Provider Test',
+              name: 'Simple Provider Test',
               widget: const ProviderTestPage()),
           const SizedBox(height: 10),
           testSectionButton(

lib/screens/provider_test.dart

@@ -1,3 +1,4 @@
+import 'package:fetchingapp/backend/firestore_changes.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
@@ -22,8 +23,18 @@ class _ProviderTestPageState extends State<ProviderTestPage> {
             const Button(fruit: 'Orange'),
             const Button(fruit: 'Banana'),
             Text(
-              'My favorite fruit is: ' + Provider.of<Favorites>(context).fruit,
+              'My favorite fruit is: ' +
+                  Provider.of<Favorites>(context).fruit +
+                  '\n\n',
               style: const TextStyle(fontSize: 25),
+            ),
+            const Text(
+              'Firestore Listener Provider:',
+              style: TextStyle(fontSize: 25),
+            ),
+            Text(
+              '\n' + Provider.of<FirestoreChanges>(context).changeStr,
+              style: const TextStyle(fontSize: 15),
             )
           ],
         ),