Camera in Flutter: solved exercise with the camera plugin

The camera plugin provides low-level access to camera hardware: real-time preview, photo capture, flash modes, zoom, and camera selection. It is the foundation for QR scanners, selfie apps, and video calls.

Problem statement

Build a camera screen that:

Shows a real-time preview with CameraPreview.
Allows switching between front and rear cameras.
Captures a photo and displays it in a thumbnail gallery.
Controls flash mode (auto, on, off, torch).
Correctly handles the CameraController lifecycle.

Dependencies

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

Android setup

In android/app/build.gradle:

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android {
    defaultConfig {
        minSdkVersion 21
    }
}

In android/app/src/main/AndroidManifest.xml:

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

iOS setup

In ios/Runner/Info.plist:

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<key>NSCameraUsageDescription</key>
<string>We need camera access to take photos</string>
<key>NSMicrophoneUsageDescription</key>
<string>We need the microphone to record video</string>

Full solution

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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';

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

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;
  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();
  }

  @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 cameras found on this device.');
      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 next = modes[(modes.indexOf(_flashMode) + 1) % modes.length];
    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('Capture error: ${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: [
            _TopBar(
              flashIcon: _flashIcon,
              onFlash: _cycleFlash,
              canSwitch: widget.cameras.length > 1,
              onSwitch: _switchCamera,
            ),
            Expanded(child: _buildPreview()),
            _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)),
    ));
  }
}

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: 'Toggle flash'),
          if (canSwitch)
            IconButton(icon: const Icon(Icons.flip_camera_ios, color: Colors.white), onPressed: onSwitch, tooltip: 'Switch camera'),
        ],
      ),
    );
  }
}

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: [
          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),
            ),
          ),
          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(),
            ),
          ),
          const SizedBox(width: 56),
        ],
      ),
    );
  }
}

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('Gallery (${_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))),
    );
  }
}

Main `CameraController` methods

Method	Description
`initialize()`	Initializes the hardware. Required before any operation
`takePicture()`	Captures a photo as `XFile`
`startVideoRecording()`	Starts video recording
`stopVideoRecording()`	Stops and returns the video as `XFile`
`setFlashMode(mode)`	Changes flash mode
`setZoomLevel(zoom)`	Adjusts zoom (between `minZoomLevel` and `maxZoomLevel`)
`setFocusPoint(offset)`	Sets focus point in normalized coordinates (0,0)–(1,1)
`setExposureOffset(value)`	Adjusts exposure in EV

Common mistakes

Not calling dispose() when leaving the screen: CameraController keeps an active sensor stream. If you don’t dispose(), the camera indicator on iOS/Android stays active and the next open fails.
Not handling WidgetsBindingObserver: when the app goes to the background, camera access may be revoked by the OS. Listen to didChangeAppLifecycleState to dispose on inactive and reinitialize on resumed.
Using XFile.path directly as a permanent path: takePicture() saves to a temporary folder that the OS may clean up. Copy the file to getApplicationDocumentsDirectory() if you need persistence.

Practical use

The camera is the foundation for: QR/barcode scanners (with mobile_scanner), document scanning apps (scan + OCR), augmented reality filters, and identity verification (KYC) in fintech apps.

Recommended next exercise

Guided practice and next step

FAQ

Can I use the `camera` plugin on the Android emulator?

Yes, but the preview will show a generated test scene, not a real camera. For real capture testing you need a physical device.

Why use `ResolutionPreset.high` instead of `max`?

ResolutionPreset.max can cause performance issues on low-end devices and significantly increase initialization time. high offers a good balance between quality and performance.

Does the `camera` plugin support QR scanning?

Not directly. For QR codes and barcodes use the mobile_scanner or qr_code_scanner plugin, which are optimized for continuous frame processing and pattern recognition.

Camera in Flutter: solved exercise with the camera plugin