Responsive design en Flutter: ejercicio resuelto con LayoutBuilder y MediaQuery

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import 'package:flutter/material.dart';

void main() => runApp(const MaterialApp(home: NewsApp()));

// ── Modelo ─────────────────────────────────────────────────────────────────────
class Article {
  final int id;
  final String title;
  final String category;
  final String body;
  final Color color;

  const Article({
    required this.id,
    required this.title,
    required this.category,
    required this.body,
    required this.color,
  });
}

const _articles = [
  Article(
    id: 1, category: 'Tecnología', color: Colors.blue,
    title: 'Flutter 4.0 llega con soporte nativo de IA',
    body: 'El equipo de Flutter ha anunciado la versión 4.0, que incluye integración '
        'nativa con modelos de lenguaje, compilación anticipada mejorada y soporte '
        'completo para Impeller en todas las plataformas.',
  ),
  Article(
    id: 2, category: 'Diseño', color: Colors.purple,
    title: 'Material You ya es el estándar de facto',
    body: 'Dos años después de su introducción, Material You se ha consolidado como '
        'el sistema de diseño preferido de los desarrolladores Android e iOS. '
        'Su sistema de color dinámico reduce el tiempo de diseño un 40%.',
  ),
  Article(
    id: 3, category: 'Backend', color: Colors.green,
    title: 'Dart en el servidor: benchmarks frente a Node.js',
    body: 'Un estudio comparativo muestra que Dart en el servidor con el framework '
        'Shelf supera a Node.js en throughput de peticiones HTTP por un 23%, '
        'con menor consumo de memoria.',
  ),
  Article(
    id: 4, category: 'Comunidad', color: Colors.orange,
    title: 'FlutterConf 2026 supera los 10 000 asistentes',
    body: 'La conferencia anual de Flutter bate su récord histórico de asistencia. '
        'Los temas más demandados fueron IA, Impeller y el nuevo sistema de '
        'compilación incremental.',
  ),
  Article(
    id: 5, category: 'Open Source', color: Colors.teal,
    title: 'Riverpod 4.0 simplifica la gestión de estado',
    body: 'La última versión de Riverpod elimina la necesidad de generar código '
        'con build_runner para la mayoría de casos de uso, reduciendo el boilerplate '
        'en un 60% según sus autores.',
  ),
];

// ── Breakpoints ────────────────────────────────────────────────────────────────
class Breakpoints {
  static const double mobile = 600;
  static const double tablet = 900;
  static const double desktop = 1200;

  static bool isMobile(double width) => width < mobile;
  static bool isTablet(double width) => width >= mobile && width < desktop;
  static bool isDesktop(double width) => width >= desktop;
}

// ── App raíz ───────────────────────────────────────────────────────────────────
class NewsApp extends StatefulWidget {
  const NewsApp({super.key});
  @override
  State<NewsApp> createState() => _NewsAppState();
}

class _NewsAppState extends State<NewsApp> {
  int _selectedIndex = 0;
  Article? _selectedArticle;

  @override
  Widget build(BuildContext context) {
    // MediaQuery.sizeOf es más eficiente que MediaQuery.of(context).size
    // (solo reconstruye al cambiar el tamaño, no ante cualquier cambio de MediaQuery)
    final width = MediaQuery.sizeOf(context).width;

    return Scaffold(
      // En escritorio mostramos NavigationRail
      body: Breakpoints.isDesktop(width)
          ? _DesktopLayout(
              selectedIndex: _selectedIndex,
              onIndexChanged: (i) => setState(() => _selectedIndex = i),
              selectedArticle: _selectedArticle,
              onArticleSelected: (a) => setState(() => _selectedArticle = a),
            )
          : _MobileTabletLayout(
              width: width,
              selectedArticle: _selectedArticle,
              onArticleSelected: (a) => setState(() => _selectedArticle = a),
            ),
      // En móvil: BottomNavigationBar
      bottomNavigationBar: Breakpoints.isMobile(width)
          ? NavigationBar(
              selectedIndex: _selectedIndex,
              onDestinationSelected: (i) => setState(() => _selectedIndex = i),
              destinations: const [
                NavigationDestination(icon: Icon(Icons.article), label: 'Noticias'),
                NavigationDestination(icon: Icon(Icons.bookmark), label: 'Guardados'),
                NavigationDestination(icon: Icon(Icons.person), label: 'Perfil'),
              ],
            )
          : null,
    );
  }
}

// ── Layout móvil / tablet ─────────────────────────────────────────────────────
class _MobileTabletLayout extends StatelessWidget {
  final double width;
  final Article? selectedArticle;
  final ValueChanged<Article> onArticleSelected;

  const _MobileTabletLayout({
    required this.width,
    required this.selectedArticle,
    required this.onArticleSelected,
  });

  @override
  Widget build(BuildContext context) {
    final isTablet = Breakpoints.isTablet(width);

    if (isTablet && selectedArticle != null) {
      // Tablet: master-detail en dos columnas
      return Row(
        children: [
          SizedBox(
            width: 360,
            child: _ArticleList(
              onArticleSelected: onArticleSelected,
              selectedId: selectedArticle!.id,
            ),
          ),
          const VerticalDivider(width: 1),
          Expanded(child: _ArticleDetail(article: selectedArticle!)),
        ],
      );
    }

    if (isTablet) {
      return Row(
        children: [
          SizedBox(
            width: 360,
            child: _ArticleList(onArticleSelected: onArticleSelected),
          ),
          const VerticalDivider(width: 1),
          const Expanded(
            child: Center(child: Text('Selecciona un artículo')),
          ),
        ],
      );
    }

    // Móvil: solo lista, detalle en ruta nueva
    return _ArticleList(
      onArticleSelected: (article) {
        Navigator.push(
          context,
          MaterialPageRoute(builder: (_) => _ArticleDetail(article: article)),
        );
      },
    );
  }
}

// ── Layout escritorio ──────────────────────────────────────────────────────────
class _DesktopLayout extends StatelessWidget {
  final int selectedIndex;
  final ValueChanged<int> onIndexChanged;
  final Article? selectedArticle;
  final ValueChanged<Article> onArticleSelected;

  const _DesktopLayout({
    required this.selectedIndex,
    required this.onIndexChanged,
    required this.selectedArticle,
    required this.onArticleSelected,
  });

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        NavigationRail(
          selectedIndex: selectedIndex,
          onDestinationSelected: onIndexChanged,
          labelType: NavigationRailLabelType.all,
          destinations: const [
            NavigationRailDestination(icon: Icon(Icons.article), label: Text('Noticias')),
            NavigationRailDestination(icon: Icon(Icons.bookmark), label: Text('Guardados')),
            NavigationRailDestination(icon: Icon(Icons.person), label: Text('Perfil')),
          ],
        ),
        const VerticalDivider(width: 1),
        SizedBox(
          width: 400,
          child: _ArticleList(
            onArticleSelected: onArticleSelected,
            selectedId: selectedArticle?.id,
          ),
        ),
        const VerticalDivider(width: 1),
        Expanded(
          child: selectedArticle != null
              ? _ArticleDetail(article: selectedArticle!)
              : const Center(child: Text('Selecciona un artículo')),
        ),
      ],
    );
  }
}

// ── Lista de artículos ─────────────────────────────────────────────────────────
class _ArticleList extends StatelessWidget {
  final ValueChanged<Article> onArticleSelected;
  final int? selectedId;

  const _ArticleList({required this.onArticleSelected, this.selectedId});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Noticias Flutter')),
      body: LayoutBuilder(
        builder: (context, constraints) {
          // Padding adaptativo según el ancho disponible de ESTE widget
          final hPadding = constraints.maxWidth > 500 ? 24.0 : 12.0;
          return ListView.separated(
            padding: EdgeInsets.symmetric(horizontal: hPadding, vertical: 12),
            itemCount: _articles.length,
            separatorBuilder: (_, __) => const SizedBox(height: 8),
            itemBuilder: (_, i) {
              final article = _articles[i];
              final isSelected = article.id == selectedId;
              return _ArticleCard(
                article: article,
                isSelected: isSelected,
                onTap: () => onArticleSelected(article),
              );
            },
          );
        },
      ),
    );
  }
}

class _ArticleCard extends StatelessWidget {
  final Article article;
  final bool isSelected;
  final VoidCallback onTap;

  const _ArticleCard({
    required this.article,
    required this.onTap,
    this.isSelected = false,
  });

  @override
  Widget build(BuildContext context) {
    return Card(
      color: isSelected
          ? Theme.of(context).colorScheme.primaryContainer
          : null,
      child: InkWell(
        onTap: onTap,
        borderRadius: BorderRadius.circular(12),
        child: Padding(
          padding: const EdgeInsets.all(12),
          child: Row(
            children: [
              CircleAvatar(
                backgroundColor: article.color.withOpacity(0.2),
                child: Icon(Icons.article, color: article.color),
              ),
              const SizedBox(width: 12),
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text(article.category,
                        style: TextStyle(
                            color: article.color,
                            fontSize: 11,
                            fontWeight: FontWeight.w600)),
                    Text(article.title,
                        maxLines: 2,
                        overflow: TextOverflow.ellipsis,
                        style: const TextStyle(fontWeight: FontWeight.bold)),
                  ],
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

// ── Detalle del artículo ───────────────────────────────────────────────────────
class _ArticleDetail extends StatelessWidget {
  final Article article;
  const _ArticleDetail({required this.article});

  @override
  Widget build(BuildContext context) {
    // LayoutBuilder para padding y tamaño de fuente adaptativo
    return LayoutBuilder(
      builder: (context, constraints) {
        final isWide = constraints.maxWidth > 600;
        final hPadding = isWide ? constraints.maxWidth * 0.1 : 24.0;
        final titleSize = isWide ? 28.0 : 22.0;

        return Scaffold(
          appBar: AppBar(title: Text(article.category)),
          body: SingleChildScrollView(
            padding: EdgeInsets.symmetric(horizontal: hPadding, vertical: 24),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Container(
                  height: isWide ? 240 : 160,
                  decoration: BoxDecoration(
                    color: article.color.withOpacity(0.15),
                    borderRadius: BorderRadius.circular(16),
                  ),
                  child: Center(
                    child: Icon(Icons.article, size: isWide ? 80 : 60,
                        color: article.color),
                  ),
                ),
                const SizedBox(height: 24),
                Text(article.title,
                    style: TextStyle(
                        fontSize: titleSize, fontWeight: FontWeight.bold)),
                const SizedBox(height: 16),
                Text(article.body,
                    style: TextStyle(
                        fontSize: isWide ? 16 : 14, height: 1.6)),
              ],
            ),
          ),
        );
      },
    );
  }
}