Plantillas de Flutter
Construyendo una aplicación de redes sociales con Flutter y Back4App

54min
Introducción
Crear una aplicación de redes sociales puede ser una tarea compleja, pero con Flutter y Back4App, puedes agilizar el proceso de desarrollo. Este tutorial te guiará a través de la construcción de una aplicación de redes sociales completa que incluye autenticación de usuarios, gestión de perfiles, feeds de noticias, conexiones de amigos, mensajería y notificaciones.
Al final de este tutorial, tendrás una aplicación de redes sociales funcional con las siguientes características:
Autenticación de Usuarios: Procesos de registro e inicio de sesión seguros.
Perfiles de Usuarios: Perfiles editables con información del usuario.
Feeds de Noticias: Mostrar publicaciones de amigos y del usuario.
Conexiones de Amigos: Capacidad para enviar y aceptar solicitudes de amistad.
Mensajería: Chat en tiempo real entre usuarios.
Notificaciones: Notificaciones push para solicitudes de amistad, mensajes e interacciones en publicaciones.
Requisitos Previos
Para seguir este tutorial, necesitarás:
Flutter SDK instalado en tu máquina. Sigue la guía oficial de instalación de Flutter para tu sistema operativo.
Conocimientos básicos de Flutter y Dart. Si eres nuevo en Flutter, revisa la documentación de Flutter para familiarizarte con los conceptos básicos.
Un IDE o editor de texto como Visual Studio Code o Android Studio.
Una cuenta de Back4App. Regístrate para obtener una cuenta gratuita en Back4App.
Parse Server SDK para Flutter agregado a tu proyecto. Aprende cómo configurarlo siguiendo la Guía del SDK de Flutter de Back4App.
Paso 1 – Configuración del Proyecto Flutter
1.1. Crear un Nuevo Proyecto Flutter
Abre tu terminal y ejecuta:
Bash
flutter create social_app
flutter create social_app
﻿
Navega al directorio del proyecto:
Bash
cd social_app
cd social_app
﻿
1.2. Agregar Dependencias
Abre pubspec.yaml y agrega las siguientes dependencias:
YAML
dependencies:
  flutter:
    sdk: flutter
  parse_server_sdk_flutter: ^4.0.1
  provider: ^6.0.0
  image_picker: ^0.8.4+6
  cached_network_image: ^3.2.0
  firebase_messaging: ^11.2.8
  uuid: ^3.0.6
dependencies:
  flutter:
    sdk: flutter
  parse_server_sdk_flutter: ^4.0.1
  provider: ^6.0.0
  image_picker: ^0.8.4+6
  cached_network_image: ^3.2.0
  firebase_messaging: ^11.2.8
  uuid: ^3.0.6
﻿
Ejecuta flutter pub get para instalar los paquetes.
Nota: Estamos usando:
parse_server_sdk_flutter para la integración con Back4App.
provider para la gestión del estado.
image_picker para seleccionar imágenes de perfil y publicaciones.
cached_network_image para una carga eficiente de imágenes.
firebase_messaging para notificaciones push.
uuid para generar IDs únicos.
Paso 2 – Configuración de Back4App
2.1. Crear una nueva aplicación de Back4App
Inicia sesión en tu panel de Back4App.
Haz clic en "Crear nueva aplicación".
Ingresa un nombre para tu aplicación, por ejemplo, "SocialApp", y haz clic en "Crear".
2.2. Configurar los modelos de datos
Necesitaremos crear varias clases en Back4App:
Usuario: Clase incorporada para la autenticación de usuarios.
Perfil: Almacena información del perfil del usuario.
Publicación: Almacena publicaciones de usuarios.
SolicitudDeAmistad: Gestiona solicitudes de amistad entre usuarios.
Mensaje: Almacena mensajes entre usuarios.
2.2.1. Clase de Perfil
Navegar a la "Base de datos" sección.
Haga clic en "Crear una clase".
En el modal:
Seleccione "Personalizado".
Ingrese "Perfil" como el nombre de la clase.
Haga clic en "Crear clase".
Agregue las siguientes columnas:
usuario: Escriba Pointer<_User>
nombreDeUsuario: Escriba String
nombreCompleto: Escriba String
biografía: Escriba String
fotoDePerfil: Escriba File
2.2.2. Clase de Publicación
Crea un "Post" clase con las siguientes columnas:
usuario: Tipo Pointer<_User>
contenido: Tipo String
imagen: Tipo File
creadoEn: Tipo Date
2.2.3. Clase FriendRequest
Crea un "FriendRequest" clase con las siguientes columnas:
deUsuario: Tipo Pointer<_User>
aUsuario: Tipo Pointer<_User>
estado: Tipo String (Valores: "pendiente", "aceptado", "rechazado")
2.2.4. Clase Message
Crea un "Message" clase con las siguientes columnas:
deUsuario: Tipo Pointer<_User>
aUsuario: Tipo Pointer<_User>
contenido: Tipo String
creadoEn: Tipo Date
2.3. Obtener Credenciales de la Aplicación
Navega a Configuración de la Aplicación > Seguridad y Claves.
Anota tu ID de Aplicación y Clave de Cliente.
Paso 3 – Inicializando Parse en tu aplicación Flutter
Abre lib/main.dart y modifícalo de la siguiente manera:
Dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import 'services/auth_service.dart';
import 'screens/login_screen.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  const keyApplicationId = 'YOUR_APPLICATION_ID';
  const keyClientKey = 'YOUR_CLIENT_KEY';
  const keyParseServerUrl = 'https://parseapi.back4app.com';

  await Parse().initialize(
    keyApplicationId,
    keyParseServerUrl,
    clientKey: keyClientKey,
    autoSendSessionId: true,
    debug: true,
  );

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<AuthService>(
      create: (_) => AuthService(),
      child: MaterialApp(
        title: 'Social App',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: LoginScreen(),
      ),
    );
  }
}
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import 'services/auth_service.dart';
import 'screens/login_screen.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  const keyApplicationId = 'YOUR_APPLICATION_ID';
  const keyClientKey = 'YOUR_CLIENT_KEY';
  const keyParseServerUrl = 'https://parseapi.back4app.com';

  await Parse().initialize(
    keyApplicationId,
    keyParseServerUrl,
    clientKey: keyClientKey,
    autoSendSessionId: true,
    debug: true,
  );

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<AuthService>(
      create: (_) => AuthService(),
      child: MaterialApp(
        title: 'Social App',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: LoginScreen(),
      ),
    );
  }
}
﻿
Reemplaza 'YOUR_APPLICATION_ID' y 'YOUR_CLIENT_KEY' con tus credenciales de Back4App.
Estamos usando ChangeNotifierProvider para gestionar el estado de autenticación.
Paso 4 – Implementando la Autenticación de Usuarios
4.1. Crear el Servicio de Autenticación
Crea un nuevo directorio llamado services bajo lib y añade un archivo llamado auth_service.dart:
Dart
// lib/services/auth_service.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class AuthService with ChangeNotifier {
  ParseUser? user;

  Future<bool> signUp(String username, String password, String email) async {
    user = ParseUser.createUser(username, password, email);

    final response = await user!.signUp();

    if (response.success) {
      notifyListeners();
      return true;
    } else {
      user = null;
      return false;
    }
  }

  Future<bool> login(String username, String password) async {
    user = ParseUser(username, password, null);

    final response = await user!.login();

    if (response.success) {
      notifyListeners();
      return true;
    } else {
      user = null;
      return false;
    }
  }

  Future<void> logout() async {
    if (user != null) {
      await user!.logout();
      user = null;
      notifyListeners();
    }
  }

  bool get isAuthenticated => user != null;
}
// lib/services/auth_service.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class AuthService with ChangeNotifier {
  ParseUser? user;

  Future<bool> signUp(String username, String password, String email) async {
    user = ParseUser.createUser(username, password, email);

    final response = await user!.signUp();

    if (response.success) {
      notifyListeners();
      return true;
    } else {
      user = null;
      return false;
    }
  }

  Future<bool> login(String username, String password) async {
    user = ParseUser(username, password, null);

    final response = await user!.login();

    if (response.success) {
      notifyListeners();
      return true;
    } else {
      user = null;
      return false;
    }
  }

  Future<void> logout() async {
    if (user != null) {
      await user!.logout();
      user = null;
      notifyListeners();
    }
  }

  bool get isAuthenticated => user != null;
}
﻿
4.2. Crear las Pantallas de Inicio de Sesión y Registro
Crea un directorio llamado screens bajo lib y añade login_screen.dart y signup_screen.dart.
4.2.1. Pantalla de inicio de sesión
Dart
// lib/screens/login_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import 'signup_screen.dart';
import 'home_screen.dart';

class LoginScreen extends StatefulWidget {
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();

  void _login() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    bool success = await authService.login(
      _usernameController.text.trim(),
      _passwordController.text.trim(),
    );

    if (success) {
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (context) => HomeScreen()),
      );
    } else {
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('Login failed')));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Social App Login'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            TextField(
              controller: _usernameController,
              decoration: InputDecoration(labelText: 'Username'),
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(height: 20),
            ElevatedButton(onPressed: _login, child: Text('Login')),
            TextButton(
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (_) => SignupScreen()),
                );
              },
              child: Text('Don\'t have an account? Sign up'),
            )
          ],
        ),
      ),
    );
  }
}
// lib/screens/login_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import 'signup_screen.dart';
import 'home_screen.dart';

class LoginScreen extends StatefulWidget {
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();

  void _login() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    bool success = await authService.login(
      _usernameController.text.trim(),
      _passwordController.text.trim(),
    );

    if (success) {
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (context) => HomeScreen()),
      );
    } else {
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('Login failed')));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Social App Login'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            TextField(
              controller: _usernameController,
              decoration: InputDecoration(labelText: 'Username'),
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(height: 20),
            ElevatedButton(onPressed: _login, child: Text('Login')),
            TextButton(
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (_) => SignupScreen()),
                );
              },
              child: Text('Don\'t have an account? Sign up'),
            )
          ],
        ),
      ),
    );
  }
}
﻿
4.2.2. Pantalla de registro
Dart
// lib/screens/signup_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import 'home_screen.dart';

class SignupScreen extends StatefulWidget {
  @override
  _SignupScreenState createState() => _SignupScreenState();
}

class _SignupScreenState extends State<SignupScreen> {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();
  final TextEditingController _emailController = TextEditingController();

  void _signUp() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    bool success = await authService.signUp(
      _usernameController.text.trim(),
      _passwordController.text.trim(),
      _emailController.text.trim(),
    );

    if (success) {
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (context) => HomeScreen()),
      );
    } else {
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('Signup failed')));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Social App Signup'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            TextField(
              controller: _usernameController,
              decoration: InputDecoration(labelText: 'Username'),
            ),
            TextField(
              controller: _emailController,
              decoration: InputDecoration(labelText: 'Email'),
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(height: 20),
            ElevatedButton(onPressed: _signUp, child: Text('Sign Up')),
          ],
        ),
      ),
    );
  }
}
// lib/screens/signup_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import 'home_screen.dart';

class SignupScreen extends StatefulWidget {
  @override
  _SignupScreenState createState() => _SignupScreenState();
}

class _SignupScreenState extends State<SignupScreen> {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();
  final TextEditingController _emailController = TextEditingController();

  void _signUp() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    bool success = await authService.signUp(
      _usernameController.text.trim(),
      _passwordController.text.trim(),
      _emailController.text.trim(),
    );

    if (success) {
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (context) => HomeScreen()),
      );
    } else {
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('Signup failed')));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Social App Signup'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            TextField(
              controller: _usernameController,
              decoration: InputDecoration(labelText: 'Username'),
            ),
            TextField(
              controller: _emailController,
              decoration: InputDecoration(labelText: 'Email'),
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(height: 20),
            ElevatedButton(onPressed: _signUp, child: Text('Sign Up')),
          ],
        ),
      ),
    );
  }
}
﻿
Paso 5 – Configuración de Perfiles de Usuario
5.1. Crear Servicio de Perfil
Agrega un archivo llamado profile_service.dart bajo lib/services/:
Dart
// lib/services/profile_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import '../models/profile.dart';

class ProfileService {
  Future<void> createProfile(ParseUser user) async {
    final profile = ParseObject('Profile')
      ..set('user', user)
      ..set('username', user.username);

    await profile.save();
  }

  Future<Profile?> getProfile(ParseUser user) async {
    final query = QueryBuilder<ParseObject>(ParseObject('Profile'))
      ..whereEqualTo('user', user);

    final response = await query.query();

    if (response.success && response.results != null) {
      final profileObject = response.results!.first;
      return Profile.fromParseObject(profileObject);
    } else {
      return null;
    }
  }

  Future<void> updateProfile(Profile profile) async {
    final profileObject = ParseObject('Profile')
      ..objectId = profile.id
      ..set('fullName', profile.fullName)
      ..set('bio', profile.bio);

    await profileObject.save();
  }
}
// lib/services/profile_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import '../models/profile.dart';

class ProfileService {
  Future<void> createProfile(ParseUser user) async {
    final profile = ParseObject('Profile')
      ..set('user', user)
      ..set('username', user.username);

    await profile.save();
  }

  Future<Profile?> getProfile(ParseUser user) async {
    final query = QueryBuilder<ParseObject>(ParseObject('Profile'))
      ..whereEqualTo('user', user);

    final response = await query.query();

    if (response.success && response.results != null) {
      final profileObject = response.results!.first;
      return Profile.fromParseObject(profileObject);
    } else {
      return null;
    }
  }

  Future<void> updateProfile(Profile profile) async {
    final profileObject = ParseObject('Profile')
      ..objectId = profile.id
      ..set('fullName', profile.fullName)
      ..set('bio', profile.bio);

    await profileObject.save();
  }
}
﻿
5.2. Crear Modelo de Perfil
Agrega un archivo llamado profile.dart bajo lib/models/:
Dart
// lib/models/profile.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class Profile {
  String id;
  String username;
  String? fullName;
  String? bio;
  ParseFileBase? profilePicture;

  Profile({
    required this.id,
    required this.username,
    this.fullName,
    this.bio,
    this.profilePicture,
  });

  factory Profile.fromParseObject(ParseObject object) {
    return Profile(
      id: object.objectId!,
      username: object.get<String>('username')!,
      fullName: object.get<String>('fullName'),
      bio: object.get<String>('bio'),
      profilePicture: object.get<ParseFileBase>('profilePicture'),
    );
  }
}
// lib/models/profile.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class Profile {
  String id;
  String username;
  String? fullName;
  String? bio;
  ParseFileBase? profilePicture;

  Profile({
    required this.id,
    required this.username,
    this.fullName,
    this.bio,
    this.profilePicture,
  });

  factory Profile.fromParseObject(ParseObject object) {
    return Profile(
      id: object.objectId!,
      username: object.get<String>('username')!,
      fullName: object.get<String>('fullName'),
      bio: object.get<String>('bio'),
      profilePicture: object.get<ParseFileBase>('profilePicture'),
    );
  }
}
﻿
5.3. Crear Pantalla de Perfil
Agrega un archivo llamado profile_screen.dart bajo lib/screens/:
Dart
// lib/screens/profile_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/profile_service.dart';
import '../models/profile.dart';

class ProfileScreen extends StatefulWidget {
  @override
  _ProfileScreenState createState() => _ProfileScreenState();
}

class _ProfileScreenState extends State<ProfileScreen> {
  final ProfileService _profileService = ProfileService();
  Profile? profile;
  final TextEditingController _fullNameController = TextEditingController();
  final TextEditingController _bioController = TextEditingController();

  void _loadProfile() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    Profile? fetchedProfile = await _profileService.getProfile(user);

    if (fetchedProfile == null) {
      await _profileService.createProfile(user);
      fetchedProfile = await _profileService.getProfile(user);
    }

    setState(() {
      profile = fetchedProfile;
      _fullNameController.text = profile?.fullName ?? '';
      _bioController.text = profile?.bio ?? '';
    });
  }

  void _saveProfile() async {
    if (profile != null) {
      profile!.fullName = _fullNameController.text.trim();
      profile!.bio = _bioController.text.trim();
      await _profileService.updateProfile(profile!);
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('Profile updated')));
    }
  }

  @override
  void initState() {
    super.initState();
    _loadProfile();
  }

  @override
  Widget build(BuildContext context) {
    if (profile == null) {
      return Scaffold(
        appBar: AppBar(title: Text('Profile')),
        body: Center(child: CircularProgressIndicator()),
      );
    }

    return Scaffold(
      appBar: AppBar(title: Text(profile!.username)),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            // Add profile picture handling here
            TextField(
              controller: _fullNameController,
              decoration: InputDecoration(labelText: 'Full Name'),
            ),
            TextField(
              controller: _bioController,
              decoration: InputDecoration(labelText: 'Bio'),
            ),
            SizedBox(height: 20),
            ElevatedButton(onPressed: _saveProfile, child: Text('Save')),
          ],
        ),
      ),
    );
  }
}
// lib/screens/profile_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/profile_service.dart';
import '../models/profile.dart';

class ProfileScreen extends StatefulWidget {
  @override
  _ProfileScreenState createState() => _ProfileScreenState();
}

class _ProfileScreenState extends State<ProfileScreen> {
  final ProfileService _profileService = ProfileService();
  Profile? profile;
  final TextEditingController _fullNameController = TextEditingController();
  final TextEditingController _bioController = TextEditingController();

  void _loadProfile() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    Profile? fetchedProfile = await _profileService.getProfile(user);

    if (fetchedProfile == null) {
      await _profileService.createProfile(user);
      fetchedProfile = await _profileService.getProfile(user);
    }

    setState(() {
      profile = fetchedProfile;
      _fullNameController.text = profile?.fullName ?? '';
      _bioController.text = profile?.bio ?? '';
    });
  }

  void _saveProfile() async {
    if (profile != null) {
      profile!.fullName = _fullNameController.text.trim();
      profile!.bio = _bioController.text.trim();
      await _profileService.updateProfile(profile!);
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('Profile updated')));
    }
  }

  @override
  void initState() {
    super.initState();
    _loadProfile();
  }

  @override
  Widget build(BuildContext context) {
    if (profile == null) {
      return Scaffold(
        appBar: AppBar(title: Text('Profile')),
        body: Center(child: CircularProgressIndicator()),
      );
    }

    return Scaffold(
      appBar: AppBar(title: Text(profile!.username)),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            // Add profile picture handling here
            TextField(
              controller: _fullNameController,
              decoration: InputDecoration(labelText: 'Full Name'),
            ),
            TextField(
              controller: _bioController,
              decoration: InputDecoration(labelText: 'Bio'),
            ),
            SizedBox(height: 20),
            ElevatedButton(onPressed: _saveProfile, child: Text('Save')),
          ],
        ),
      ),
    );
  }
}
﻿
Paso 6 – Implementando Fuentes de Noticias
6.1. Crear Servicio de Publicación
Agrega un archivo llamado post_service.dart en lib/services/:
Dart
// lib/services/post_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import '../models/post.dart';

class PostService {
  Future<void> createPost(String content, ParseUser user) async {
    final post = ParseObject('Post')
      ..set('user', user)
      ..set('content', content);

    await post.save();
  }

  Future<List<Post>> getPosts(ParseUser user) async {
    final query = QueryBuilder<ParseObject>(ParseObject('Post'))
      ..orderByDescending('createdAt')
      ..includeObject(['user']);

    final response = await query.query();

    if (response.success && response.results != null) {
      return response.results!.map((e) => Post.fromParseObject(e)).toList();
    } else {
      return [];
    }
  }
}
// lib/services/post_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import '../models/post.dart';

class PostService {
  Future<void> createPost(String content, ParseUser user) async {
    final post = ParseObject('Post')
      ..set('user', user)
      ..set('content', content);

    await post.save();
  }

  Future<List<Post>> getPosts(ParseUser user) async {
    final query = QueryBuilder<ParseObject>(ParseObject('Post'))
      ..orderByDescending('createdAt')
      ..includeObject(['user']);

    final response = await query.query();

    if (response.success && response.results != null) {
      return response.results!.map((e) => Post.fromParseObject(e)).toList();
    } else {
      return [];
    }
  }
}
﻿
6.2. Crear Modelo de Publicación
Agrega un archivo llamado post.dart en lib/models/:
Dart
// lib/models/post.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class Post {
  String id;
  String content;
  ParseUser user;
  DateTime createdAt;

  Post({
    required this.id,
    required this.content,
    required this.user,
    required this.createdAt,
  });

  factory Post.fromParseObject(ParseObject object) {
    return Post(
      id: object.objectId!,
      content: object.get<String>('content')!,
      user: object.get<ParseUser>('user')!,
      createdAt: object.createdAt!,
    );
  }
}
// lib/models/post.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class Post {
  String id;
  String content;
  ParseUser user;
  DateTime createdAt;

  Post({
    required this.id,
    required this.content,
    required this.user,
    required this.createdAt,
  });

  factory Post.fromParseObject(ParseObject object) {
    return Post(
      id: object.objectId!,
      content: object.get<String>('content')!,
      user: object.get<ParseUser>('user')!,
      createdAt: object.createdAt!,
    );
  }
}
﻿
6.3. Crear Pantalla de Inicio
Modificar home_screen.dart bajo lib/screens/:
Dart
// lib/screens/home_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/post_service.dart';
import '../models/post.dart';
import 'profile_screen.dart';

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  final PostService _postService = PostService();
  List<Post> posts = [];
  final TextEditingController _postController = TextEditingController();

  void _loadPosts() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    List<Post> fetchedPosts = await _postService.getPosts(user);

    setState(() {
      posts = fetchedPosts;
    });
  }

  void _createPost() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    await _postService.createPost(_postController.text.trim(), user);
    _postController.clear();
    _loadPosts();
  }

  @override
  void initState() {
    super.initState();
    _loadPosts();
  }

  @override
  Widget build(BuildContext context) {
    final authService = Provider.of<AuthService>(context);
    return Scaffold(
      appBar: AppBar(
        title: Text('Social App'),
        actions: [
          IconButton(
            icon: Icon(Icons.person),
            onPressed: () {
              Navigator.push(
                context,
                MaterialPageRoute(builder: (_) => ProfileScreen()),
              );
            },
          ),
          IconButton(
            icon: Icon(Icons.logout),
            onPressed: () async {
              await authService.logout();
              Navigator.pushReplacementNamed(context, '/');
            },
          ),
        ],
      ),
      body: Column(
        children: [
          TextField(
            controller: _postController,
            decoration: InputDecoration(
              hintText: 'What\'s on your mind?',
              contentPadding: EdgeInsets.all(16),
            ),
          ),
          ElevatedButton(onPressed: _createPost, child: Text('Post')),
          Expanded(
            child: ListView.builder(
              itemCount: posts.length,
              itemBuilder: (context, index) {
                final post = posts[index];
                return ListTile(
                  title: Text(post.user.username ?? 'Unknown'),
                  subtitle: Text(post.content),
                  trailing: Text(
                    post.createdAt.toLocal().toString(),
                    style: TextStyle(fontSize: 12),
                  ),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}
// lib/screens/home_screen.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/post_service.dart';
import '../models/post.dart';
import 'profile_screen.dart';

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  final PostService _postService = PostService();
  List<Post> posts = [];
  final TextEditingController _postController = TextEditingController();

  void _loadPosts() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    List<Post> fetchedPosts = await _postService.getPosts(user);

    setState(() {
      posts = fetchedPosts;
    });
  }

  void _createPost() async {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    await _postService.createPost(_postController.text.trim(), user);
    _postController.clear();
    _loadPosts();
  }

  @override
  void initState() {
    super.initState();
    _loadPosts();
  }

  @override
  Widget build(BuildContext context) {
    final authService = Provider.of<AuthService>(context);
    return Scaffold(
      appBar: AppBar(
        title: Text('Social App'),
        actions: [
          IconButton(
            icon: Icon(Icons.person),
            onPressed: () {
              Navigator.push(
                context,
                MaterialPageRoute(builder: (_) => ProfileScreen()),
              );
            },
          ),
          IconButton(
            icon: Icon(Icons.logout),
            onPressed: () async {
              await authService.logout();
              Navigator.pushReplacementNamed(context, '/');
            },
          ),
        ],
      ),
      body: Column(
        children: [
          TextField(
            controller: _postController,
            decoration: InputDecoration(
              hintText: 'What\'s on your mind?',
              contentPadding: EdgeInsets.all(16),
            ),
          ),
          ElevatedButton(onPressed: _createPost, child: Text('Post')),
          Expanded(
            child: ListView.builder(
              itemCount: posts.length,
              itemBuilder: (context, index) {
                final post = posts[index];
                return ListTile(
                  title: Text(post.user.username ?? 'Unknown'),
                  subtitle: Text(post.content),
                  trailing: Text(
                    post.createdAt.toLocal().toString(),
                    style: TextStyle(fontSize: 12),
                  ),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}
﻿
Paso 7 – Agregando Conexiones de Amigos
En este paso, implementaremos conexiones de amigos entre usuarios. Los usuarios pueden enviar solicitudes de amistad, aceptarlas o rechazarlas, y ver su lista de amigos. Modificaremos los modelos de datos, crearemos servicios y actualizaremos la interfaz de usuario para soportar esta funcionalidad.
7.1. Actualizar el Modelo de Datos
Ya hemos creado la FriendRequest clase en Back4App con las siguientes columnas:
fromUser: Puntero a _User
toUser: Puntero a _User
status: Cadena (Valores: "pendiente", "aceptado", "rechazado")
Además, necesitamos rastrear la lista de amigos de un usuario. Podemos hacer esto agregando una friends relación en la _User clase.
7.1.1. Agregar relación de amigos a la clase de usuario
En Back4App, ve a la User clase.
Haz clic en el "+" botón para agregar una nueva columna.
Nombra la columna "friends" y establece el tipo en Relation <_User>.
7.2. Crear servicio de solicitud de amistad
Crea un archivo llamado friend_service.dart en lib/services/:
Dart
// lib/services/friend_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class FriendService {
  Future<bool> sendFriendRequest(ParseUser fromUser, ParseUser toUser) async {
    final friendRequest = ParseObject('FriendRequest')
      ..set('fromUser', fromUser)
      ..set('toUser', toUser)
      ..set('status', 'pending');

    final response = await friendRequest.save();
    return response.success;
  }

  Future<List<ParseObject>> getPendingRequests(ParseUser user) async {
    final query = QueryBuilder<ParseObject>(ParseObject('FriendRequest'))
      ..whereEqualTo('toUser', user)
      ..whereEqualTo('status', 'pending')
      ..includeObject(['fromUser']);

    final response = await query.query();
    if (response.success && response.results != null) {
      return response.results!;
    } else {
      return [];
    }
  }

  Future<bool> acceptFriendRequest(ParseObject friendRequest) async {
    friendRequest.set('status', 'accepted');
    final response = await friendRequest.save();

    if (response.success) {
      // Add each user to the other's friends relation
      final fromUser = friendRequest.get<ParseUser>('fromUser')!;
      final toUser = friendRequest.get<ParseUser>('toUser')!;

      fromUser.setAdd('friends', [toUser]);
      toUser.setAdd('friends', [fromUser]);

      await fromUser.save();
      await toUser.save();

      return true;
    }
    return false;
  }

  Future<bool> rejectFriendRequest(ParseObject friendRequest) async {
    friendRequest.set('status', 'rejected');
    final response = await friendRequest.save();
    return response.success;
  }

  Future<List<ParseUser>> getFriends(ParseUser user) async {
    final relation = user.getRelation<ParseUser>('friends');
    final query = relation.query();

    final response = await query.query();
    if (response.success && response.results != null) {
      return response.results!.cast<ParseUser>();
    } else {
      return [];
    }
  }
}
// lib/services/friend_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class FriendService {
  Future<bool> sendFriendRequest(ParseUser fromUser, ParseUser toUser) async {
    final friendRequest = ParseObject('FriendRequest')
      ..set('fromUser', fromUser)
      ..set('toUser', toUser)
      ..set('status', 'pending');

    final response = await friendRequest.save();
    return response.success;
  }

  Future<List<ParseObject>> getPendingRequests(ParseUser user) async {
    final query = QueryBuilder<ParseObject>(ParseObject('FriendRequest'))
      ..whereEqualTo('toUser', user)
      ..whereEqualTo('status', 'pending')
      ..includeObject(['fromUser']);

    final response = await query.query();
    if (response.success && response.results != null) {
      return response.results!;
    } else {
      return [];
    }
  }

  Future<bool> acceptFriendRequest(ParseObject friendRequest) async {
    friendRequest.set('status', 'accepted');
    final response = await friendRequest.save();

    if (response.success) {
      // Add each user to the other's friends relation
      final fromUser = friendRequest.get<ParseUser>('fromUser')!;
      final toUser = friendRequest.get<ParseUser>('toUser')!;

      fromUser.setAdd('friends', [toUser]);
      toUser.setAdd('friends', [fromUser]);

      await fromUser.save();
      await toUser.save();

      return true;
    }
    return false;
  }

  Future<bool> rejectFriendRequest(ParseObject friendRequest) async {
    friendRequest.set('status', 'rejected');
    final response = await friendRequest.save();
    return response.success;
  }

  Future<List<ParseUser>> getFriends(ParseUser user) async {
    final relation = user.getRelation<ParseUser>('friends');
    final query = relation.query();

    final response = await query.query();
    if (response.success && response.results != null) {
      return response.results!.cast<ParseUser>();
    } else {
      return [];
    }
  }
}
﻿
7.3. Actualizar la interfaz de usuario
7.3.1. Agregar pantalla de búsqueda de usuarios
Crea un archivo llamado search_users_screen.dart en lib/screens/:
Dart
// lib/screens/search_users_screen.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/friend_service.dart';

class SearchUsersScreen extends StatefulWidget {
  @override
  _SearchUsersScreenState createState() => _SearchUsersScreenState();
}

class _SearchUsersScreenState extends State<SearchUsersScreen> {
  final TextEditingController _searchController = TextEditingController();
  List<ParseUser> users = [];
  final FriendService _friendService = FriendService();

  void _searchUsers() async {
    final query = QueryBuilder<ParseUser>(ParseUser.forQuery())
      ..whereContains('username', _searchController.text.trim())
      ..whereNotEqualTo('objectId', Provider.of<AuthService>(context, listen: false).user!.objectId);

    final response = await query.query();
    if (response.success && response.results != null) {
      setState(() {
        users = response.results!.cast<ParseUser>();
      });
    } else {
      setState(() {
        users = [];
      });
    }
  }

  void _sendFriendRequest(ParseUser toUser) async {
    final fromUser = Provider.of<AuthService>(context, listen: false).user!;
    bool success = await _friendService.sendFriendRequest(fromUser, toUser);
    if (success) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Friend request sent')));
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to send friend request')));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Search Users'),
      ),
      body: Column(
        children: [
          Padding(
            padding: const EdgeInsets.all(16.0),
            child: TextField(
              controller: _searchController,
              decoration: InputDecoration(
                hintText: 'Search by username',
                suffixIcon: IconButton(
                  icon: Icon(Icons.search),
                  onPressed: _searchUsers,
                ),
              ),
            ),
          ),
          Expanded(
            child: ListView.builder(
              itemCount: users.length,
              itemBuilder: (context, index) {
                final user = users[index];
                return ListTile(
                  title: Text(user.username ?? 'Unknown'),
                  trailing: ElevatedButton(
                    onPressed: () => _sendFriendRequest(user),
                    child: Text('Add Friend'),
                  ),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}
// lib/screens/search_users_screen.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/friend_service.dart';

class SearchUsersScreen extends StatefulWidget {
  @override
  _SearchUsersScreenState createState() => _SearchUsersScreenState();
}

class _SearchUsersScreenState extends State<SearchUsersScreen> {
  final TextEditingController _searchController = TextEditingController();
  List<ParseUser> users = [];
  final FriendService _friendService = FriendService();

  void _searchUsers() async {
    final query = QueryBuilder<ParseUser>(ParseUser.forQuery())
      ..whereContains('username', _searchController.text.trim())
      ..whereNotEqualTo('objectId', Provider.of<AuthService>(context, listen: false).user!.objectId);

    final response = await query.query();
    if (response.success && response.results != null) {
      setState(() {
        users = response.results!.cast<ParseUser>();
      });
    } else {
      setState(() {
        users = [];
      });
    }
  }

  void _sendFriendRequest(ParseUser toUser) async {
    final fromUser = Provider.of<AuthService>(context, listen: false).user!;
    bool success = await _friendService.sendFriendRequest(fromUser, toUser);
    if (success) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Friend request sent')));
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to send friend request')));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Search Users'),
      ),
      body: Column(
        children: [
          Padding(
            padding: const EdgeInsets.all(16.0),
            child: TextField(
              controller: _searchController,
              decoration: InputDecoration(
                hintText: 'Search by username',
                suffixIcon: IconButton(
                  icon: Icon(Icons.search),
                  onPressed: _searchUsers,
                ),
              ),
            ),
          ),
          Expanded(
            child: ListView.builder(
              itemCount: users.length,
              itemBuilder: (context, index) {
                final user = users[index];
                return ListTile(
                  title: Text(user.username ?? 'Unknown'),
                  trailing: ElevatedButton(
                    onPressed: () => _sendFriendRequest(user),
                    child: Text('Add Friend'),
                  ),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}
﻿
7.3.2. Agregar Pantalla de Solicitudes de Amistad
Crea un archivo llamado friend_requests_screen.dart bajo lib/screens/:
Dart
// lib/screens/friend_requests_screen.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/friend_service.dart';

class FriendRequestsScreen extends StatefulWidget {
  @override
  _FriendRequestsScreenState createState() => _FriendRequestsScreenState();
}

class _FriendRequestsScreenState extends State<FriendRequestsScreen> {
  final FriendService _friendService = FriendService();
  List<ParseObject> friendRequests = [];

  void _loadFriendRequests() async {
    final user = Provider.of<AuthService>(context, listen: false).user!;
    final requests = await _friendService.getPendingRequests(user);
    setState(() {
      friendRequests = requests;
    });
  }

  void _acceptRequest(ParseObject request) async {
    bool success = await _friendService.acceptFriendRequest(request);
    if (success) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Friend request accepted')));
      _loadFriendRequests();
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to accept friend request')));
    }
  }

  void _rejectRequest(ParseObject request) async {
    bool success = await _friendService.rejectFriendRequest(request);
    if (success) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Friend request rejected')));
      _loadFriendRequests();
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to reject friend request')));
    }
  }

  @override
  void initState() {
    super.initState();
    _loadFriendRequests();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Friend Requests'),
      ),
      body: ListView.builder(
        itemCount: friendRequests.length,
        itemBuilder: (context, index) {
          final request = friendRequests[index];
          final fromUser = request.get<ParseUser>('fromUser')!;
          return ListTile(
            title: Text(fromUser.username ?? 'Unknown'),
            subtitle: Text('Sent you a friend request'),
            trailing: Row(
              mainAxisSize: MainAxisSize.min,
              children: [
                IconButton(
                  icon: Icon(Icons.check, color: Colors.green),
                  onPressed: () => _acceptRequest(request),
                ),
                IconButton(
                  icon: Icon(Icons.close, color: Colors.red),
                  onPressed: () => _rejectRequest(request),
                ),
              ],
            ),
          );
        },
      ),
    );
  }
}
// lib/screens/friend_requests_screen.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import '../services/auth_service.dart';
import '../services/friend_service.dart';

class FriendRequestsScreen extends StatefulWidget {
  @override
  _FriendRequestsScreenState createState() => _FriendRequestsScreenState();
}

class _FriendRequestsScreenState extends State<FriendRequestsScreen> {
  final FriendService _friendService = FriendService();
  List<ParseObject> friendRequests = [];

  void _loadFriendRequests() async {
    final user = Provider.of<AuthService>(context, listen: false).user!;
    final requests = await _friendService.getPendingRequests(user);
    setState(() {
      friendRequests = requests;
    });
  }

  void _acceptRequest(ParseObject request) async {
    bool success = await _friendService.acceptFriendRequest(request);
    if (success) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Friend request accepted')));
      _loadFriendRequests();
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to accept friend request')));
    }
  }

  void _rejectRequest(ParseObject request) async {
    bool success = await _friendService.rejectFriendRequest(request);
    if (success) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Friend request rejected')));
      _loadFriendRequests();
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to reject friend request')));
    }
  }

  @override
  void initState() {
    super.initState();
    _loadFriendRequests();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Friend Requests'),
      ),
      body: ListView.builder(
        itemCount: friendRequests.length,
        itemBuilder: (context, index) {
          final request = friendRequests[index];
          final fromUser = request.get<ParseUser>('fromUser')!;
          return ListTile(
            title: Text(fromUser.username ?? 'Unknown'),
            subtitle: Text('Sent you a friend request'),
            trailing: Row(
              mainAxisSize: MainAxisSize.min,
              children: [
                IconButton(
                  icon: Icon(Icons.check, color: Colors.green),
                  onPressed: () => _acceptRequest(request),
                ),
                IconButton(
                  icon: Icon(Icons.close, color: Colors.red),
                  onPressed: () => _rejectRequest(request),
                ),
              ],
            ),
          );
        },
      ),
    );
  }
}
﻿
7.3.3. Actualizar Navegación de la Pantalla de Inicio
En home_screen.dart, agrega navegación a las pantallas de búsqueda de usuarios y solicitudes de amistad:
Dart
// Inside AppBar actions
IconButton(
  icon: Icon(Icons.person_add),
  onPressed: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => SearchUsersScreen()),
    );
  },
),
IconButton(
  icon: Icon(Icons.notifications),
  onPressed: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => FriendRequestsScreen()),
    );
  },
),
// Inside AppBar actions
IconButton(
  icon: Icon(Icons.person_add),
  onPressed: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => SearchUsersScreen()),
    );
  },
),
IconButton(
  icon: Icon(Icons.notifications),
  onPressed: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => FriendRequestsScreen()),
    );
  },
),
﻿
7.4. Actualizar el Feed de Noticias para Mostrar las Publicaciones de Amigos
Modifica el getPosts método en post_service.dart para obtener publicaciones del usuario y sus amigos.
Dart
// lib/services/post_service.dart
Future<List<Post>> getPosts(ParseUser user) async {
  // Get friends
  final relation = user.getRelation<ParseUser>('friends');
  final friendsQuery = relation.query();

  final friendsResponse = await friendsQuery.query();

  List<String> userIds = [user.objectId!];
  if (friendsResponse.success && friendsResponse.results != null) {
    final friends = friendsResponse.results!.cast<ParseUser>();
    userIds.addAll(friends.map((friend) => friend.objectId!));
  }

  // Fetch posts from user and friends
  final query = QueryBuilder<ParseObject>(ParseObject('Post'))
    ..whereContainedIn('user', userIds.map((id) => ParseUser(null, null, null)..objectId = id).toList())
    ..orderByDescending('createdAt')
    ..includeObject(['user']);

  final response = await query.query();

  if (response.success && response.results != null) {
    return response.results!.map((e) => Post.fromParseObject(e)).toList();
  } else {
    return [];
  }
}
// lib/services/post_service.dart
Future<List<Post>> getPosts(ParseUser user) async {
  // Get friends
  final relation = user.getRelation<ParseUser>('friends');
  final friendsQuery = relation.query();

  final friendsResponse = await friendsQuery.query();

  List<String> userIds = [user.objectId!];
  if (friendsResponse.success && friendsResponse.results != null) {
    final friends = friendsResponse.results!.cast<ParseUser>();
    userIds.addAll(friends.map((friend) => friend.objectId!));
  }

  // Fetch posts from user and friends
  final query = QueryBuilder<ParseObject>(ParseObject('Post'))
    ..whereContainedIn('user', userIds.map((id) => ParseUser(null, null, null)..objectId = id).toList())
    ..orderByDescending('createdAt')
    ..includeObject(['user']);

  final response = await query.query();

  if (response.success && response.results != null) {
    return response.results!.map((e) => Post.fromParseObject(e)).toList();
  } else {
    return [];
  }
}
﻿
Paso 8 – Implementación de Mensajería
En este paso, agregaremos mensajería en tiempo real entre los usuarios utilizando Consultas en Vivo.
8.1. Habilitar Consultas en Vivo en Back4App
En el panel de control de tu aplicación Back4App, ve a Configuración de la Aplicación > Configuración del Servidor.
Bajo URL del Servidor, anota tu URL del servidor (por ejemplo, https://YOUR_APP_NAME.back4app.io).
Las Consultas en Vivo están habilitadas por defecto en Back4App.
8.2. Configurar Consultas en Vivo en Flutter
El parse_server_sdk_flutter paquete incluye soporte para Consultas en Vivo.
8.3. Crear Servicio de Mensajería
Crea un archivo llamado message_service.dart bajo lib/services/:
Dart
// lib/services/message_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import '../models/message.dart';

class MessageService {
  ParseLiveList<Message>? liveMessageList;

  Future<void> sendMessage(ParseUser fromUser, ParseUser toUser, String content) async {
    final message = ParseObject('Message')
      ..set('fromUser', fromUser)
      ..set('toUser', toUser)
      ..set('content', content);

    await message.save();
  }

  Future<void> subscribeToMessages(ParseUser user, ParseUser otherUser, Function(List<Message>) onMessagesUpdated) async {
    final queryBuilder = QueryBuilder<ParseObject>(ParseObject('Message'))
      ..whereEqualTo('fromUser', user)
      ..whereEqualTo('toUser', otherUser)
      ..orderByAscending('createdAt')
      ..includeObject(['fromUser', 'toUser']);

    liveMessageList = ParseLiveList<Message>(queryBuilder, listenOnAllSubItems: true);

    liveMessageList!.stream.listen((event) {
      onMessagesUpdated(liveMessageList!.items);
    });
  }

  Future<void> dispose() async {
    await liveMessageList?.dispose();
  }
}
// lib/services/message_service.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import '../models/message.dart';

class MessageService {
  ParseLiveList<Message>? liveMessageList;

  Future<void> sendMessage(ParseUser fromUser, ParseUser toUser, String content) async {
    final message = ParseObject('Message')
      ..set('fromUser', fromUser)
      ..set('toUser', toUser)
      ..set('content', content);

    await message.save();
  }

  Future<void> subscribeToMessages(ParseUser user, ParseUser otherUser, Function(List<Message>) onMessagesUpdated) async {
    final queryBuilder = QueryBuilder<ParseObject>(ParseObject('Message'))
      ..whereEqualTo('fromUser', user)
      ..whereEqualTo('toUser', otherUser)
      ..orderByAscending('createdAt')
      ..includeObject(['fromUser', 'toUser']);

    liveMessageList = ParseLiveList<Message>(queryBuilder, listenOnAllSubItems: true);

    liveMessageList!.stream.listen((event) {
      onMessagesUpdated(liveMessageList!.items);
    });
  }

  Future<void> dispose() async {
    await liveMessageList?.dispose();
  }
}
﻿
8.4. Crear Modelo de Mensaje
Agrega un archivo llamado message.dart bajo lib/models/:
Dart
// lib/models/message.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class Message extends ParseObject implements ParseCloneable {
  Message() : super('Message');

  Message.clone() : this();

  @override
  clone(Map<String, dynamic> map) => Message.clone()..fromJson(map);

  ParseUser get fromUser => get<ParseUser>('fromUser')!;
  ParseUser get toUser => get<ParseUser>('toUser')!;
  String get content => get<String>('content')!;
}
// lib/models/message.dart
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class Message extends ParseObject implements ParseCloneable {
  Message() : super('Message');

  Message.clone() : this();

  @override
  clone(Map<String, dynamic> map) => Message.clone()..fromJson(map);

  ParseUser get fromUser => get<ParseUser>('fromUser')!;
  ParseUser get toUser => get<ParseUser>('toUser')!;
  String get content => get<String>('content')!;
}
﻿
8.5. Crear Pantalla de Chat
Agrega un archivo llamado chat_screen.dart bajo lib/screens/:
Dart
// lib/screens/chat_screen.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import '../models/message.dart';
import '../services/auth_service.dart';
import '../services/message_service.dart';

class ChatScreen extends StatefulWidget {
  final ParseUser otherUser;

  ChatScreen({required this.otherUser});

  @override
  _ChatScreenState createState() => _ChatScreenState();
}

class _ChatScreenState extends State<ChatScreen> {
  final MessageService _messageService = MessageService();
  List<Message> messages = [];
  final TextEditingController _messageController = TextEditingController();

  void _sendMessage() {
    final authService = Provider.of<AuthService>(context, listen: false);
    final fromUser = authService.user!;
    final toUser = widget.otherUser;

    _messageService.sendMessage(fromUser, toUser, _messageController.text.trim());
    _messageController.clear();
  }

  void _onMessagesUpdated(List<Message> updatedMessages) {
    setState(() {
      messages = updatedMessages;
    });
  }

  @override
  void initState() {
    super.initState();
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    _messageService.subscribeToMessages(user, widget.otherUser, _onMessagesUpdated);
  }

  @override
  void dispose() {
    _messageService.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;

    return Scaffold(
      appBar: AppBar(title: Text(widget.otherUser.username ?? 'Chat')),
      body: Column(
        children: [
          Expanded(
            child: ListView(
              children: messages.map((message) {
                bool isMe = message.fromUser.objectId == user.objectId;
                return ListTile(
                  title: Align(
                    alignment: isMe ? Alignment.centerRight : Alignment.centerLeft,
                    child: Container(
                      padding: EdgeInsets.all(10),
                      color: isMe ? Colors.blueAccent : Colors.grey[300],
                      child: Text(
                        message.content,
                        style: TextStyle(color: isMe ? Colors.white : Colors.black),
                      ),
                    ),
                  ),
                );
              }).toList(),
            ),
          ),
          Divider(height: 1),
          Container(
            padding: EdgeInsets.symmetric(horizontal: 8.0),
            color: Theme.of(context).cardColor,
            child: Row(
              children: [
                Flexible(
                  child: TextField(
                    controller: _messageController,
                    decoration: InputDecoration.collapsed(hintText: 'Send a message'),
                  ),
                ),
                IconButton(
                  icon: Icon(Icons.send),
                  onPressed: _sendMessage,
                ),
              ],
            ),
          )
        ],
      ),
    );
  }
}
// lib/screens/chat_screen.dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:provider/provider.dart';
import '../models/message.dart';
import '../services/auth_service.dart';
import '../services/message_service.dart';

class ChatScreen extends StatefulWidget {
  final ParseUser otherUser;

  ChatScreen({required this.otherUser});

  @override
  _ChatScreenState createState() => _ChatScreenState();
}

class _ChatScreenState extends State<ChatScreen> {
  final MessageService _messageService = MessageService();
  List<Message> messages = [];
  final TextEditingController _messageController = TextEditingController();

  void _sendMessage() {
    final authService = Provider.of<AuthService>(context, listen: false);
    final fromUser = authService.user!;
    final toUser = widget.otherUser;

    _messageService.sendMessage(fromUser, toUser, _messageController.text.trim());
    _messageController.clear();
  }

  void _onMessagesUpdated(List<Message> updatedMessages) {
    setState(() {
      messages = updatedMessages;
    });
  }

  @override
  void initState() {
    super.initState();
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;
    _messageService.subscribeToMessages(user, widget.otherUser, _onMessagesUpdated);
  }

  @override
  void dispose() {
    _messageService.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final authService = Provider.of<AuthService>(context, listen: false);
    final user = authService.user!;

    return Scaffold(
      appBar: AppBar(title: Text(widget.otherUser.username ?? 'Chat')),
      body: Column(
        children: [
          Expanded(
            child: ListView(
              children: messages.map((message) {
                bool isMe = message.fromUser.objectId == user.objectId;
                return ListTile(
                  title: Align(
                    alignment: isMe ? Alignment.centerRight : Alignment.centerLeft,
                    child: Container(
                      padding: EdgeInsets.all(10),
                      color: isMe ? Colors.blueAccent : Colors.grey[300],
                      child: Text(
                        message.content,
                        style: TextStyle(color: isMe ? Colors.white : Colors.black),
                      ),
                    ),
                  ),
                );
              }).toList(),
            ),
          ),
          Divider(height: 1),
          Container(
            padding: EdgeInsets.symmetric(horizontal: 8.0),
            color: Theme.of(context).cardColor,
            child: Row(
              children: [
                Flexible(
                  child: TextField(
                    controller: _messageController,
                    decoration: InputDecoration.collapsed(hintText: 'Send a message'),
                  ),
                ),
                IconButton(
                  icon: Icon(Icons.send),
                  onPressed: _sendMessage,
                ),
              ],
            ),
          )
        ],
      ),
    );
  }
}
﻿
8.6. Actualizar UI para Iniciar Chat
Puedes iniciar el chat desde la lista de amigos o la pantalla de búsqueda de usuarios.
En la lista de amigos, al mostrar amigos, añade un botón para iniciar un chat:
Dart
// Inside the ListTile for a friend
trailing: IconButton(
  icon: Icon(Icons.chat),
  onPressed: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => ChatScreen(otherUser: friend)),
    );
  },
),
// Inside the ListTile for a friend
trailing: IconButton(
  icon: Icon(Icons.chat),
  onPressed: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => ChatScreen(otherUser: friend)),
    );
  },
),
﻿
Paso 9 – Añadiendo Notificaciones Push
Implementar notificaciones push implica configurar Firebase Cloud Messaging (FCM) e integrarlo con Back4App.
9.1. Configurar Firebase Cloud Messaging
9.1.1. Configurar el Proyecto de Firebase
Ve a Firebase Console y crea un nuevo proyecto.
Agrega una aplicación de Android y/o iOS a tu proyecto.
Para Android, necesitas el nombre del paquete (applicationId).
Para iOS, necesitas el Identificador del Paquete.
9.1.2. Descargar Archivos de Configuración
Para Android: Descarga google-services.json y colócalo en android/app/.
Para iOS: Descarga GoogleService-Info.plist y agrégalo a tu proyecto de Xcode bajo Runner.
9.2. Agregar firebase_messaging Paquete
Asegúrate de haber agregado firebase_messaging a tu pubspec.yaml:
YAML
dependencies:
  firebase_messaging: ^11.2.8
dependencies:
  firebase_messaging: ^11.2.8
﻿
Ejecuta flutter pub get para instalar.
9.3. Inicializar Firebase en Flutter
Modificar main.dart:
Dart
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:firebase_core/firebase_core.dart';
// Other imports

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  // Initialize Parse as before

  runApp(MyApp());
}
import 'package:flutter/material.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';
import 'package:firebase_core/firebase_core.dart';
// Other imports

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  // Initialize Parse as before

  runApp(MyApp());
}
﻿
9.4. Configurar Firebase Messaging
Crear un archivo llamado push_notification_service.dart bajo lib/services/:
Dart
// lib/services/push_notification_service.dart
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class PushNotificationService {
  final FirebaseMessaging _fcm = FirebaseMessaging.instance;

  Future<void> init() async {
    // Request permissions (iOS)
    await _fcm.requestPermission();

    // Get the token
    String? token = await _fcm.getToken();

    if (token != null) {
      // Save the token to Parse Installation
      final installation = await ParseInstallation.currentInstallation();
      installation.set('deviceToken', token);
      await installation.save();
    }

    // Handle foreground messages
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      print('Received a message in the foreground!');
      // Handle the message
    });
  }
}
// lib/services/push_notification_service.dart
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:parse_server_sdk_flutter/parse_server_sdk.dart';

class PushNotificationService {
  final FirebaseMessaging _fcm = FirebaseMessaging.instance;

  Future<void> init() async {
    // Request permissions (iOS)
    await _fcm.requestPermission();

    // Get the token
    String? token = await _fcm.getToken();

    if (token != null) {
      // Save the token to Parse Installation
      final installation = await ParseInstallation.currentInstallation();
      installation.set('deviceToken', token);
      await installation.save();
    }

    // Handle foreground messages
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      print('Received a message in the foreground!');
      // Handle the message
    });
  }
}
﻿
9.5. Actualizar main.dart para inicializar las notificaciones push
En main.dart, después de inicializar Parse, inicializar el PushNotificationService:
Dart
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  // Initialize Parse as before

  // Initialize Push Notifications
  PushNotificationService _pushNotificationService = PushNotificationService();
  await _pushNotificationService.init();

  runApp(MyApp());
}
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  // Initialize Parse as before

  // Initialize Push Notifications
  PushNotificationService _pushNotificationService = PushNotificationService();
  await _pushNotificationService.init();

  runApp(MyApp());
}
﻿
9.6. Enviar Notificaciones Push desde Back4App
Puedes enviar notificaciones push usando Cloud Code o directamente desde tu servidor.
9.6.1. Enviando Notificación en Solicitud de Amistad
Cuando un usuario envía una solicitud de amistad, puedes enviar una notificación push al destinatario.
En friend_service.dart, modifica el sendFriendRequest método:
Dart
Future<bool> sendFriendRequest(ParseUser fromUser, ParseUser toUser) async {
  // Existing code to create friend request

  // Send push notification
  final pushQuery = QueryBuilder<ParseInstallation>(ParseInstallation.forQuery())
    ..whereEqualTo('user', toUser);

  await ParsePush().send(
    PushPayload(
      query: pushQuery,
      notification: ParseNotification(
        title: 'New Friend Request',
        alert: '${fromUser.username} sent you a friend request',
      ),
    ),
  );

  return response.success;
}
Future<bool> sendFriendRequest(ParseUser fromUser, ParseUser toUser) async {
  // Existing code to create friend request

  // Send push notification
  final pushQuery = QueryBuilder<ParseInstallation>(ParseInstallation.forQuery())
    ..whereEqualTo('user', toUser);

  await ParsePush().send(
    PushPayload(
      query: pushQuery,
      notification: ParseNotification(
        title: 'New Friend Request',
        alert: '${fromUser.username} sent you a friend request',
      ),
    ),
  );

  return response.success;
}
﻿
Nota: Asegúrate de haber asociado la instalación con el usuario.
9.7. Asociar Instalación con Usuario
Cuando un usuario inicie sesión, asocia su instalación con su cuenta de usuario.
En auth_service.dart, después de un inicio de sesión exitoso:
Dart
Future<bool> login(String username, String password) async {
  user = ParseUser(username, password, null);

  final response = await user!.login();

  if (response.success) {
    // Associate installation with user
    final installation = await ParseInstallation.currentInstallation();
    installation.set('user', user);
    await installation.save();

    notifyListeners();
    return true;
  } else {
    user = null;
    return false;
  }
}
Future<bool> login(String username, String password) async {
  user = ParseUser(username, password, null);

  final response = await user!.login();

  if (response.success) {
    // Associate installation with user
    final installation = await ParseInstallation.currentInstallation();
    installation.set('user', user);
    await installation.save();

    notifyListeners();
    return true;
  } else {
    user = null;
    return false;
  }
}
﻿
Nota: Las notificaciones push requieren una configuración adicional tanto en el lado del cliente como en el del servidor. Necesitas manejar diferentes escenarios, como notificaciones en segundo plano y permisos de usuario, que están más allá del alcance de este tutorial.
﻿
Conclusión
¡Felicidades! Has construido la base de una aplicación de redes sociales utilizando Flutter y Back4App. Esta aplicación incluye autenticación de usuarios, gestión de perfiles y una función de feed de noticias. Si bien la implementación de conexiones completas de amigos, mensajería y notificaciones está más allá del alcance de este tutorial, ahora tienes la estructura necesaria para seguir expandiendo tu aplicación.
Próximos Pasos
Conexiones de Amigos: Implementar funcionalidades de solicitudes de amistad.
Mensajería: Agregar funciones de chat en tiempo real utilizando Live Queries.
Notificaciones: Integrar notificaciones push para el compromiso del usuario.
Mejoras de UI: Mejorar la interfaz de usuario y la experiencia del usuario.
Seguridad: Asegurar la seguridad y privacidad de los datos estableciendo ACLs apropiados en Back4App.
Recursos Adicionales
﻿Documentación de Back4App﻿
﻿Guía de Parse SDK para Flutter﻿
﻿Documentación Oficial de Flutter﻿
﻿Documentación del Paquete Provider﻿
¡Feliz Codificación!
Actualizado 23 Jan 2025
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