Cámara en Flutter: ejercicio resuelto con el plugin camera

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dependencies:
  camera: ^0.11.0+2
  path_provider: ^2.1.4
  path: ^1.9.0

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android {
    defaultConfig {
        minSdkVersion 21
    }
}

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<uses-permission android:name="android.permission.CAMERA"/>

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<key>NSCameraUsageDescription</key>
<string>Necesitamos acceso a la cámara para tomar fotos</string>
<key>NSMicrophoneUsageDescription</key>
<string>Necesitamos el micrófono para grabar vídeo</string>

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import 'dart:io';

import 'package:camera/camera.dart';
import 'package:flutter/material.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';

// ── Entrada de la app ──────────────────────────────────────────────────────────
Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final cameras = await availableCameras();
  runApp(MaterialApp(home: CameraScreen(cameras: cameras)));
}

// ── Pantalla principal de cámara ───────────────────────────────────────────────
class CameraScreen extends StatefulWidget {
  final List<CameraDescription> cameras;
  const CameraScreen({super.key, required this.cameras});

  @override
  State<CameraScreen> createState() => _CameraScreenState();
}

class _CameraScreenState extends State<CameraScreen>
    with WidgetsBindingObserver {
  CameraController? _controller;
  int _cameraIndex = 0; // 0 = trasera, 1 = frontal (si existe)
  FlashMode _flashMode = FlashMode.auto;
  bool _isCapturing = false;
  final List<String> _capturedPaths = [];
  String? _initError;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    _initCamera();
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    _controller?.dispose();
    super.dispose();
  }

  // Pausar/reanudar la cámara con el ciclo de vida de la app
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    final ctrl = _controller;
    if (ctrl == null || !ctrl.value.isInitialized) return;

    if (state == AppLifecycleState.inactive) {
      ctrl.dispose();
    } else if (state == AppLifecycleState.resumed) {
      _initCamera();
    }
  }

  Future<void> _initCamera() async {
    if (widget.cameras.isEmpty) {
      setState(() => _initError = 'No se encontraron cámaras en este dispositivo.');
      return;
    }

    final camera = widget.cameras[_cameraIndex];
    final ctrl = CameraController(
      camera,
      ResolutionPreset.high,
      enableAudio: false,
      imageFormatGroup: ImageFormatGroup.jpeg,
    );

    try {
      await ctrl.initialize();
      await ctrl.setFlashMode(_flashMode);
      if (!mounted) return;
      setState(() {
        _controller = ctrl;
        _initError = null;
      });
    } on CameraException catch (e) {
      setState(() => _initError = '${e.code}: ${e.description}');
    }
  }

  Future<void> _switchCamera() async {
    if (widget.cameras.length < 2) return;
    await _controller?.dispose();
    setState(() {
      _cameraIndex = (_cameraIndex + 1) % widget.cameras.length;
      _controller = null;
    });
    await _initCamera();
  }

  Future<void> _cycleFlash() async {
    final modes = [FlashMode.auto, FlashMode.always, FlashMode.off, FlashMode.torch];
    final nextIndex = (modes.indexOf(_flashMode) + 1) % modes.length;
    final next = modes[nextIndex];
    await _controller?.setFlashMode(next);
    setState(() => _flashMode = next);
  }

  Future<void> _takePicture() async {
    final ctrl = _controller;
    if (ctrl == null || !ctrl.value.isInitialized || _isCapturing) return;

    setState(() => _isCapturing = true);

    try {
      final dir = await getTemporaryDirectory();
      final path = p.join(dir.path, '${DateTime.now().millisecondsSinceEpoch}.jpg');

      final file = await ctrl.takePicture();
      await File(file.path).copy(path);

      setState(() => _capturedPaths.insert(0, path));
    } on CameraException catch (e) {
      if (mounted) {
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(content: Text('Error al capturar: ${e.description}')),
        );
      }
    } finally {
      setState(() => _isCapturing = false);
    }
  }

  IconData get _flashIcon => switch (_flashMode) {
        FlashMode.auto => Icons.flash_auto,
        FlashMode.always => Icons.flash_on,
        FlashMode.off => Icons.flash_off,
        FlashMode.torch => Icons.highlight,
        _ => Icons.flash_auto,
      };

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: SafeArea(
        child: Column(
          children: [
            // ── Barra superior ───────────────────────────────────────────
            _TopBar(
              flashIcon: _flashIcon,
              onFlash: _cycleFlash,
              canSwitch: widget.cameras.length > 1,
              onSwitch: _switchCamera,
            ),

            // ── Previsualización ─────────────────────────────────────────
            Expanded(child: _buildPreview()),

            // ── Controles inferiores ─────────────────────────────────────
            _BottomControls(
              isCapturing: _isCapturing,
              onCapture: _takePicture,
              lastCapturePath: _capturedPaths.isNotEmpty ? _capturedPaths.first : null,
              onShowGallery: _capturedPaths.isEmpty
                  ? null
                  : () => _showGallery(context),
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildPreview() {
    if (_initError != null) {
      return Center(
        child: Padding(
          padding: const EdgeInsets.all(24),
          child: Text(
            _initError!,
            style: const TextStyle(color: Colors.red),
            textAlign: TextAlign.center,
          ),
        ),
      );
    }

    final ctrl = _controller;
    if (ctrl == null || !ctrl.value.isInitialized) {
      return const Center(child: CircularProgressIndicator(color: Colors.white));
    }

    return ClipRect(
      child: OverflowBox(
        alignment: Alignment.center,
        child: FittedBox(
          fit: BoxFit.cover,
          child: SizedBox(
            width: ctrl.value.previewSize?.height ?? 1,
            height: ctrl.value.previewSize?.width ?? 1,
            child: CameraPreview(ctrl),
          ),
        ),
      ),
    );
  }

  void _showGallery(BuildContext context) {
    Navigator.of(context).push(
      MaterialPageRoute(
        builder: (_) => _GalleryScreen(paths: List.from(_capturedPaths)),
      ),
    );
  }
}

// ── Barra superior ─────────────────────────────────────────────────────────────
class _TopBar extends StatelessWidget {
  final IconData flashIcon;
  final VoidCallback onFlash;
  final bool canSwitch;
  final VoidCallback onSwitch;

  const _TopBar({
    required this.flashIcon,
    required this.onFlash,
    required this.canSwitch,
    required this.onSwitch,
  });

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: [
          IconButton(
            icon: Icon(flashIcon, color: Colors.white),
            onPressed: onFlash,
            tooltip: 'Cambiar flash',
          ),
          if (canSwitch)
            IconButton(
              icon: const Icon(Icons.flip_camera_ios, color: Colors.white),
              onPressed: onSwitch,
              tooltip: 'Cambiar cámara',
            ),
        ],
      ),
    );
  }
}

// ── Controles inferiores ───────────────────────────────────────────────────────
class _BottomControls extends StatelessWidget {
  final bool isCapturing;
  final VoidCallback onCapture;
  final String? lastCapturePath;
  final VoidCallback? onShowGallery;

  const _BottomControls({
    required this.isCapturing,
    required this.onCapture,
    this.lastCapturePath,
    this.onShowGallery,
  });

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 16),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: [
          // Miniatura de última captura → galería
          GestureDetector(
            onTap: onShowGallery,
            child: Container(
              width: 56,
              height: 56,
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(8),
                border: Border.all(color: Colors.white54),
                color: Colors.white12,
              ),
              child: lastCapturePath != null
                  ? ClipRRect(
                      borderRadius: BorderRadius.circular(7),
                      child: Image.file(File(lastCapturePath!), fit: BoxFit.cover),
                    )
                  : const Icon(Icons.photo_library, color: Colors.white54),
            ),
          ),

          // Botón de captura
          GestureDetector(
            onTap: isCapturing ? null : onCapture,
            child: AnimatedContainer(
              duration: const Duration(milliseconds: 150),
              width: isCapturing ? 64 : 72,
              height: isCapturing ? 64 : 72,
              decoration: BoxDecoration(
                shape: BoxShape.circle,
                color: Colors.white,
                border: Border.all(color: Colors.white54, width: 4),
              ),
              child: isCapturing
                  ? const Padding(
                      padding: EdgeInsets.all(16),
                      child: CircularProgressIndicator(strokeWidth: 2),
                    )
                  : const SizedBox.shrink(),
            ),
          ),

          // Placeholder para centrar el botón de captura
          const SizedBox(width: 56),
        ],
      ),
    );
  }
}

// ── Galería de capturas ────────────────────────────────────────────────────────
class _GalleryScreen extends StatefulWidget {
  final List<String> paths;
  const _GalleryScreen({required this.paths});
  @override
  State<_GalleryScreen> createState() => _GalleryScreenState();
}

class _GalleryScreenState extends State<_GalleryScreen> {
  late final List<String> _paths = List.from(widget.paths);

  void _delete(String path) {
    File(path).deleteSync();
    setState(() => _paths.remove(path));
    if (_paths.isEmpty && mounted) Navigator.of(context).pop();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Galería (${_paths.length})'),
        backgroundColor: Colors.black,
        foregroundColor: Colors.white,
      ),
      backgroundColor: Colors.black,
      body: GridView.builder(
        padding: const EdgeInsets.all(4),
        gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 3,
          crossAxisSpacing: 4,
          mainAxisSpacing: 4,
        ),
        itemCount: _paths.length,
        itemBuilder: (_, i) {
          final path = _paths[i];
          return GestureDetector(
            onTap: () => Navigator.of(context).push(
              MaterialPageRoute(
                builder: (_) => _PhotoViewer(path: path, onDelete: () => _delete(path)),
              ),
            ),
            child: Image.file(File(path), fit: BoxFit.cover),
          );
        },
      ),
    );
  }
}

class _PhotoViewer extends StatelessWidget {
  final String path;
  final VoidCallback onDelete;
  const _PhotoViewer({required this.path, required this.onDelete});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      appBar: AppBar(
        backgroundColor: Colors.black,
        foregroundColor: Colors.white,
        actions: [
          IconButton(
            icon: const Icon(Icons.delete, color: Colors.red),
            onPressed: () {
              onDelete();
              Navigator.of(context).pop();
            },
          ),
        ],
      ),
      body: Center(child: Image.file(File(path))),
    );
  }
}