flutter_hooks en Flutter: ejercicio resuelto con useState y useEffect

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# pubspec.yaml
dependencies:
  flutter:
    sdk: flutter
  flutter_hooks: ^0.21.0

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import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';

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

class _DemoPage extends StatelessWidget {
  const _DemoPage();

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 3,
      child: Scaffold(
        appBar: AppBar(
          title: const Text('flutter_hooks demo'),
          bottom: const TabBar(tabs: [
            Tab(text: 'Cronómetro'),
            Tab(text: 'Buscador'),
            Tab(text: 'Countdown'),
          ]),
        ),
        body: const TabBarView(children: [
          StopwatchPage(),
          SearchPage(),
          CountdownPage(),
        ]),
      ),
    );
  }
}

// ── 1. Cronómetro con useState + useEffect ────────────────────────────────────
class StopwatchPage extends HookWidget {
  const StopwatchPage({super.key});

  @override
  Widget build(BuildContext context) {
    final elapsed = useState(Duration.zero);   // equivale a setState
    final running = useState(false);

    // useEffect: se ejecuta cuando cambia [running.value]
    // Devuelve la función de cleanup (cancela el Timer al desmontar o al cambiar)
    useEffect(() {
      if (!running.value) return null;
      final timer = Timer.periodic(const Duration(milliseconds: 10), (_) {
        elapsed.value += const Duration(milliseconds: 10);
      });
      return timer.cancel;  // cleanup
    }, [running.value]);

    final minutes = elapsed.value.inMinutes.toString().padLeft(2, '0');
    final seconds = (elapsed.value.inSeconds % 60).toString().padLeft(2, '0');
    final millis = ((elapsed.value.inMilliseconds % 1000) ~/ 10).toString().padLeft(2, '0');

    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          Text('$minutes:$seconds.$millis',
              style: const TextStyle(fontSize: 64, fontFamily: 'monospace')),
          const SizedBox(height: 32),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              FilledButton(
                onPressed: () => running.value = !running.value,
                child: Text(running.value ? 'Pausar' : 'Iniciar'),
              ),
              const SizedBox(width: 16),
              OutlinedButton(
                onPressed: () {
                  running.value = false;
                  elapsed.value = Duration.zero;
                },
                child: const Text('Resetear'),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

// ── 2. Buscador reactivo con useTextEditingController + useMemoized ───────────
const _fruits = [
  'Manzana', 'Mango', 'Melón', 'Melocotón', 'Mora',
  'Plátano', 'Pera', 'Piña', 'Papaya', 'Pomelo',
  'Naranja', 'Nectarina', 'Níspero',
  'Fresa', 'Frambuesa', 'Arándano', 'Cereza',
];

class SearchPage extends HookWidget {
  const SearchPage({super.key});

  @override
  Widget build(BuildContext context) {
    final controller = useTextEditingController();
    // useValueListenable convierte el controller en un valor reactivo
    final query = useValueListenable(controller);

    // useMemoized recalcula solo cuando cambia el texto
    final filtered = useMemoized(
      () => _fruits
          .where((f) => f.toLowerCase().contains(query.text.toLowerCase()))
          .toList(),
      [query.text],
    );

    return Column(
      children: [
        Padding(
          padding: const EdgeInsets.all(12),
          child: TextField(
            controller: controller,
            decoration: const InputDecoration(
              prefixIcon: Icon(Icons.search),
              hintText: 'Buscar fruta...',
              border: OutlineInputBorder(),
            ),
          ),
        ),
        Expanded(
          child: ListView.builder(
            itemCount: filtered.length,
            itemBuilder: (_, i) => ListTile(title: Text(filtered[i])),
          ),
        ),
      ],
    );
  }
}

// ── 3. Hook personalizado: useCountdown ───────────────────────────────────────
/// Devuelve los segundos restantes de una cuenta atrás.
/// Se reinicia automáticamente al terminar si [loop] es true.
int useCountdown(int seconds, {bool loop = false}) {
  final remaining = useState(seconds);

  useEffect(() {
    final timer = Timer.periodic(const Duration(seconds: 1), (_) {
      if (remaining.value > 0) {
        remaining.value--;
      } else if (loop) {
        remaining.value = seconds;
      }
    });
    return timer.cancel;
  }, const []);  // [] = solo al montar/desmontar

  return remaining.value;
}

class CountdownPage extends HookWidget {
  const CountdownPage({super.key});

  @override
  Widget build(BuildContext context) {
    final secs = useCountdown(60, loop: true);

    final color = secs > 30
        ? Colors.green
        : secs > 10
            ? Colors.orange
            : Colors.red;

    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          TweenAnimationBuilder<double>(
            tween: Tween(begin: 1, end: secs / 60),
            duration: const Duration(milliseconds: 900),
            builder: (_, value, __) => CircularProgressIndicator(
              value: value,
              color: color,
              strokeWidth: 8,
              strokeCap: StrokeCap.round,
            ),
          ),
          const SizedBox(height: 24),
          Text('$secs segundos',
              style: TextStyle(
                  fontSize: 40, fontWeight: FontWeight.bold, color: color)),
          const SizedBox(height: 8),
          const Text('Se reinicia en bucle automáticamente',
              style: TextStyle(color: Colors.grey)),
        ],
      ),
    );
  }
}