Flutter Camera Plugin Advanced Example WITHOUT NULL SAFETY

main.dart

// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// ignore_for_file: public_member_api_docs

import 'dart:async';
import 'dart:io';

import 'package:camera/camera.dart';
import 'package:flutter/material.dart';
import 'package:video_player/video_player.dart';

class CameraExampleHome extends StatefulWidget {
  @override
  _CameraExampleHomeState createState() {
    return _CameraExampleHomeState();
  }
}

/// Returns a suitable camera icon for [direction].
IconData getCameraLensIcon(CameraLensDirection direction) {
  switch (direction) {
    case CameraLensDirection.back:
      return Icons.camera_rear;
    case CameraLensDirection.front:
      return Icons.camera_front;
    case CameraLensDirection.external:
      return Icons.camera;
    default:
      throw ArgumentError('Unknown lens direction');
  }
}

void logError(String code, String message) {
  if (message != null) {
    print('Error: $code\nError Message: $message');
  } else {
    print('Error: $code');
  }
}

class _CameraExampleHomeState extends State<CameraExampleHome>
    with WidgetsBindingObserver, TickerProviderStateMixin {
  CameraController controller;
  XFile imageFile;
  XFile videoFile;
  VideoPlayerController videoController;
  VoidCallback videoPlayerListener;
  bool enableAudio = true;
  double _minAvailableExposureOffset = 0.0;
  double _maxAvailableExposureOffset = 0.0;
  double _currentExposureOffset = 0.0;
  AnimationController _flashModeControlRowAnimationController;
  Animation<double> _flashModeControlRowAnimation;
  AnimationController _exposureModeControlRowAnimationController;
  Animation<double> _exposureModeControlRowAnimation;
  AnimationController _focusModeControlRowAnimationController;
  Animation<double> _focusModeControlRowAnimation;
  double _minAvailableZoom = 1.0;
  double _maxAvailableZoom = 1.0;
  double _currentScale = 1.0;
  double _baseScale = 1.0;

  // Counting pointers (number of user fingers on screen)
  int _pointers = 0;

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

    // FAILS TO WORK WITHOUT FOLLOWING BLOCK OF CODE
    // START BLOCK
    controller = CameraController(cameras[0], ResolutionPreset.max);
    controller.initialize().then((_) {
      if (!mounted) {
        return;
      }
      setState(() {});
    });
    // END BLOCK

    WidgetsBinding.instance.addObserver(this);

    _flashModeControlRowAnimationController = AnimationController(
      duration: const Duration(milliseconds: 300),
      vsync: this,
    );
    _flashModeControlRowAnimation = CurvedAnimation(
      parent: _flashModeControlRowAnimationController,
      curve: Curves.easeInCubic,
    );
    _exposureModeControlRowAnimationController = AnimationController(
      duration: const Duration(milliseconds: 300),
      vsync: this,
    );
    _exposureModeControlRowAnimation = CurvedAnimation(
      parent: _exposureModeControlRowAnimationController,
      curve: Curves.easeInCubic,
    );
    _focusModeControlRowAnimationController = AnimationController(
      duration: const Duration(milliseconds: 300),
      vsync: this,
    );
    _focusModeControlRowAnimation = CurvedAnimation(
      parent: _focusModeControlRowAnimationController,
      curve: Curves.easeInCubic,
    );
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    _flashModeControlRowAnimationController.dispose();
    _exposureModeControlRowAnimationController.dispose();
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    final CameraController cameraController = controller;

    // App state changed before we got the chance to initialize.
    if (cameraController == null || !cameraController.value.isInitialized) {
      return;
    }

    if (state == AppLifecycleState.inactive) {
      cameraController.dispose();
    } else if (state == AppLifecycleState.resumed) {
      onNewCameraSelected(cameraController.description);
    }
  }

  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: const Text('Camera example'),
      ),
      body: Column(
        children: <Widget>[
          Expanded(
            child: Container(
              child: Padding(
                padding: const EdgeInsets.all(1.0),
                child: Center(
                  child: _cameraPreviewWidget(),
                ),
              ),
              decoration: BoxDecoration(
                color: Colors.black,
                border: Border.all(
                  color:
                  controller != null && controller.value.isRecordingVideo
                      ? Colors.redAccent
                      : Colors.grey,
                  width: 3.0,
                ),
              ),
            ),
          ),
          _captureControlRowWidget(),
          _modeControlRowWidget(),
          Padding(
            padding: const EdgeInsets.all(5.0),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.start,
              children: <Widget>[
                _cameraTogglesRowWidget(),
                _thumbnailWidget(),
              ],
            ),
          ),
        ],
      ),
    );
  }

  /// Display the preview from the camera (or a message if the preview is not available).
  Widget _cameraPreviewWidget() {
    final CameraController cameraController = controller;

    if (cameraController == null || !cameraController.value.isInitialized) {
      return const Text(
        'Tap a camera',
        style: TextStyle(
          color: Colors.white,
          fontSize: 24.0,
          fontWeight: FontWeight.w900,
        ),
      );
    } else {
      return Listener(
        onPointerDown: (_) => _pointers++,
        onPointerUp: (_) => _pointers--,
        child: CameraPreview(
          controller,
          child: LayoutBuilder(
              builder: (BuildContext context, BoxConstraints constraints) {
                return GestureDetector(
                  behavior: HitTestBehavior.opaque,
                  onScaleStart: _handleScaleStart,
                  onScaleUpdate: _handleScaleUpdate,
                  onTapDown: (details) => onViewFinderTap(details, constraints),
                );
              }),
        ),
      );
    }
  }

  void _handleScaleStart(ScaleStartDetails details) {
    _baseScale = _currentScale;
  }

  Future<void> _handleScaleUpdate(ScaleUpdateDetails details) async {
    // When there are not exactly two fingers on screen don't scale
    if (controller == null || _pointers != 2) {
      return;
    }

    _currentScale = (_baseScale * details.scale)
        .clamp(_minAvailableZoom, _maxAvailableZoom);

    await controller.setZoomLevel(_currentScale);
  }

  /// Display the thumbnail of the captured image or video.
  Widget _thumbnailWidget() {
    final VideoPlayerController localVideoController = videoController;

    return Expanded(
      child: Align(
        alignment: Alignment.centerRight,
        child: Row(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            localVideoController == null && imageFile == null
                ? Container()
                : SizedBox(
              child: (localVideoController == null)
                  ? Image.file(File(imageFile.path))
                  : Container(
                child: Center(
                  child: AspectRatio(
                      aspectRatio:
                      localVideoController.value.size != null
                          ? localVideoController
                          .value.aspectRatio
                          : 1.0,
                      child: VideoPlayer(localVideoController)),
                ),
                decoration: BoxDecoration(
                    border: Border.all(color: Colors.pink)),
              ),
              width: 64.0,
              height: 64.0,
            ),
          ],
        ),
      ),
    );
  }

  /// Display a bar with buttons to change the flash and exposure modes
  Widget _modeControlRowWidget() {
    return Column(
      children: [
        Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          mainAxisSize: MainAxisSize.max,
          children: <Widget>[
            IconButton(
              icon: Icon(Icons.flash_on),
              color: Colors.blue,
              onPressed: controller != null ? onFlashModeButtonPressed : null,
            ),
            IconButton(
              icon: Icon(Icons.exposure),
              color: Colors.blue,
              onPressed:
              controller != null ? onExposureModeButtonPressed : null,
            ),
            IconButton(
              icon: Icon(Icons.filter_center_focus),
              color: Colors.blue,
              onPressed: controller != null ? onFocusModeButtonPressed : null,
            ),
            IconButton(
              icon: Icon(enableAudio ? Icons.volume_up : Icons.volume_mute),
              color: Colors.blue,
              onPressed: controller != null ? onAudioModeButtonPressed : null,
            ),
            IconButton(
              icon: Icon(controller.value.isCaptureOrientationLocked ?? false
                  ? Icons.screen_lock_rotation
                  : Icons.screen_rotation),
              color: Colors.blue,
              onPressed: controller != null
                  ? onCaptureOrientationLockButtonPressed
                  : null,
            ),
          ],
        ),
        _flashModeControlRowWidget(),
        _exposureModeControlRowWidget(),
        _focusModeControlRowWidget(),
      ],
    );
  }

  Widget _flashModeControlRowWidget() {
    return SizeTransition(
      sizeFactor: _flashModeControlRowAnimation,
      child: ClipRect(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          mainAxisSize: MainAxisSize.max,
          children: [
            IconButton(
              icon: Icon(Icons.flash_off),
              color: controller.value.flashMode == FlashMode.off
                  ? Colors.orange
                  : Colors.blue,
              onPressed: controller != null
                  ? () => onSetFlashModeButtonPressed(FlashMode.off)
                  : null,
            ),
            IconButton(
              icon: Icon(Icons.flash_auto),
              color: controller.value.flashMode == FlashMode.auto
                  ? Colors.orange
                  : Colors.blue,
              onPressed: controller != null
                  ? () => onSetFlashModeButtonPressed(FlashMode.auto)
                  : null,
            ),
            IconButton(
              icon: Icon(Icons.flash_on),
              color: controller.value.flashMode == FlashMode.always
                  ? Colors.orange
                  : Colors.blue,
              onPressed: controller != null
                  ? () => onSetFlashModeButtonPressed(FlashMode.always)
                  : null,
            ),
            IconButton(
              icon: Icon(Icons.highlight),
              color: controller.value.flashMode == FlashMode.torch
                  ? Colors.orange
                  : Colors.blue,
              onPressed: controller != null
                  ? () => onSetFlashModeButtonPressed(FlashMode.torch)
                  : null,
            ),
          ],
        ),
      ),
    );
  }

  Widget _exposureModeControlRowWidget() {
    final ButtonStyle styleAuto = TextButton.styleFrom(
      primary: controller.value.exposureMode == ExposureMode.auto
          ? Colors.orange
          : Colors.blue,
    );
    final ButtonStyle styleLocked = TextButton.styleFrom(
      primary: controller.value.exposureMode == ExposureMode.locked
          ? Colors.orange
          : Colors.blue,
    );

    return SizeTransition(
      sizeFactor: _exposureModeControlRowAnimation,
      child: ClipRect(
        child: Container(
          color: Colors.grey.shade50,
          child: Column(
            children: [
              Center(
                child: Text("Exposure Mode"),
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                mainAxisSize: MainAxisSize.max,
                children: [
                  TextButton(
                    child: Text('AUTO'),
                    style: styleAuto,
                    onPressed: controller != null
                        ? () =>
                        onSetExposureModeButtonPressed(ExposureMode.auto)
                        : null,
                    onLongPress: () {
                      if (controller != null) {
                        controller.setExposurePoint(null);
                        showInSnackBar('Resetting exposure point');
                      }
                    },
                  ),
                  TextButton(
                    child: Text('LOCKED'),
                    style: styleLocked,
                    onPressed: controller != null
                        ? () =>
                        onSetExposureModeButtonPressed(ExposureMode.locked)
                        : null,
                  ),
                ],
              ),
              Center(
                child: Text("Exposure Offset"),
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                mainAxisSize: MainAxisSize.max,
                children: [
                  Text(_minAvailableExposureOffset.toString()),
                  Slider(
                    value: _currentExposureOffset,
                    min: _minAvailableExposureOffset,
                    max: _maxAvailableExposureOffset,
                    label: _currentExposureOffset.toString(),
                    onChanged: _minAvailableExposureOffset ==
                        _maxAvailableExposureOffset
                        ? null
                        : setExposureOffset,
                  ),
                  Text(_maxAvailableExposureOffset.toString()),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }

  Widget _focusModeControlRowWidget() {
    final ButtonStyle styleAuto = TextButton.styleFrom(
      primary: controller?.value.focusMode == FocusMode.auto
          ? Colors.orange
          : Colors.blue,
    );
    final ButtonStyle styleLocked = TextButton.styleFrom(
      primary: controller.value.focusMode == FocusMode.locked
          ? Colors.orange
          : Colors.blue,
    );

    return SizeTransition(
      sizeFactor: _focusModeControlRowAnimation,
      child: ClipRect(
        child: Container(
          color: Colors.grey.shade50,
          child: Column(
            children: [
              Center(
                child: Text("Focus Mode"),
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                mainAxisSize: MainAxisSize.max,
                children: [
                  TextButton(
                    child: Text('AUTO'),
                    style: styleAuto,
                    onPressed: controller != null
                        ? () => onSetFocusModeButtonPressed(FocusMode.auto)
                        : null,
                    onLongPress: () {
                      if (controller != null) controller.setFocusPoint(null);
                      showInSnackBar('Resetting focus point');
                    },
                  ),
                  TextButton(
                    child: Text('LOCKED'),
                    style: styleLocked,
                    onPressed: controller != null
                        ? () => onSetFocusModeButtonPressed(FocusMode.locked)
                        : null,
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }

  /// Display the control bar with buttons to take pictures and record videos.
  Widget _captureControlRowWidget() {
    final CameraController cameraController = controller;

    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      mainAxisSize: MainAxisSize.max,
      children: <Widget>[
        IconButton(
          icon: const Icon(Icons.camera_alt),
          color: Colors.blue,
          onPressed: cameraController != null &&
              cameraController.value.isInitialized &&
              !cameraController.value.isRecordingVideo
              ? onTakePictureButtonPressed
              : null,
        ),
        IconButton(
          icon: const Icon(Icons.videocam),
          color: Colors.blue,
          onPressed: cameraController != null &&
              cameraController.value.isInitialized &&
              !cameraController.value.isRecordingVideo
              ? onVideoRecordButtonPressed
              : null,
        ),
        IconButton(
          icon: cameraController != null &&
              cameraController.value.isRecordingPaused
              ? Icon(Icons.play_arrow)
              : Icon(Icons.pause),
          color: Colors.blue,
          onPressed: cameraController != null &&
              cameraController.value.isInitialized &&
              cameraController.value.isRecordingVideo
              ? (cameraController.value.isRecordingPaused)
              ? onResumeButtonPressed
              : onPauseButtonPressed
              : null,
        ),
        IconButton(
          icon: const Icon(Icons.stop),
          color: Colors.red,
          onPressed: cameraController != null &&
              cameraController.value.isInitialized &&
              cameraController.value.isRecordingVideo
              ? onStopButtonPressed
              : null,
        )
      ],
    );
  }

  /// Display a row of toggle to select the camera (or a message if no camera is available).
  Widget _cameraTogglesRowWidget() {
    final List<Widget> toggles = <Widget>[];

    final onChanged = (CameraDescription description) {
      if (description == null) {
        return;
      }

      onNewCameraSelected(description);
    };

    if (cameras.isEmpty) {
      return const Text('No camera found');
    } else {
      for (CameraDescription cameraDescription in cameras) {
        toggles.add(
          SizedBox(
            width: 90.0,
            child: RadioListTile<CameraDescription>(
              title: Icon(getCameraLensIcon(cameraDescription.lensDirection)),
              groupValue: controller.description,
              value: cameraDescription,
              onChanged:
              controller != null && controller.value.isRecordingVideo
                  ? null
                  : onChanged,
            ),
          ),
        );
      }
    }

    return Row(children: toggles);
  }

  String timestamp() => DateTime.now().millisecondsSinceEpoch.toString();

  void showInSnackBar(String message) {
    // ignore: deprecated_member_use
    _scaffoldKey.currentState.showSnackBar(SnackBar(content: Text(message)));
  }

  void onViewFinderTap(TapDownDetails details, BoxConstraints constraints) {
    if (controller == null) {
      return;
    }

    final CameraController cameraController = controller;

    final offset = Offset(
      details.localPosition.dx / constraints.maxWidth,
      details.localPosition.dy / constraints.maxHeight,
    );
    cameraController.setExposurePoint(offset);
    cameraController.setFocusPoint(offset);
  }

  void onNewCameraSelected(CameraDescription cameraDescription) async {
    if (controller != null) {
      await controller.dispose();
    }
    final CameraController cameraController = CameraController(
      cameraDescription,
      ResolutionPreset.medium,
      enableAudio: enableAudio,
      imageFormatGroup: ImageFormatGroup.jpeg,
    );
    controller = cameraController;

    // If the controller is updated then update the UI.
    cameraController.addListener(() {
      if (mounted) setState(() {});
      if (cameraController.value.hasError) {
        showInSnackBar(
            'Camera error ${cameraController.value.errorDescription}');
      }
    });

    try {
      await cameraController.initialize();
      await Future.wait([
        cameraController
            .getMinExposureOffset()
            .then((value) => _minAvailableExposureOffset = value),
        cameraController
            .getMaxExposureOffset()
            .then((value) => _maxAvailableExposureOffset = value),
        cameraController
            .getMaxZoomLevel()
            .then((value) => _maxAvailableZoom = value),
        cameraController
            .getMinZoomLevel()
            .then((value) => _minAvailableZoom = value),
      ]);
    } on CameraException catch (e) {
      _showCameraException(e);
    }

    if (mounted) {
      setState(() {});
    }
  }

  void onTakePictureButtonPressed() {
    takePicture().then((XFile file) {
      if (mounted) {
        setState(() {
          imageFile = file;
          videoController.dispose();
          videoController = null;
        });
        if (file != null) showInSnackBar('Picture saved to ${file.path}');
      }
    });
  }

  void onFlashModeButtonPressed() {
    if (_flashModeControlRowAnimationController.value == 1) {
      _flashModeControlRowAnimationController.reverse();
    } else {
      _flashModeControlRowAnimationController.forward();
      _exposureModeControlRowAnimationController.reverse();
      _focusModeControlRowAnimationController.reverse();
    }
  }

  void onExposureModeButtonPressed() {
    if (_exposureModeControlRowAnimationController.value == 1) {
      _exposureModeControlRowAnimationController.reverse();
    } else {
      _exposureModeControlRowAnimationController.forward();
      _flashModeControlRowAnimationController.reverse();
      _focusModeControlRowAnimationController.reverse();
    }
  }

  void onFocusModeButtonPressed() {
    if (_focusModeControlRowAnimationController.value == 1) {
      _focusModeControlRowAnimationController.reverse();
    } else {
      _focusModeControlRowAnimationController.forward();
      _flashModeControlRowAnimationController.reverse();
      _exposureModeControlRowAnimationController.reverse();
    }
  }

  void onAudioModeButtonPressed() {
    enableAudio = !enableAudio;
    if (controller != null) {
      onNewCameraSelected(controller.description);
    }
  }

  void onCaptureOrientationLockButtonPressed() async {
    if (controller != null) {
      final CameraController cameraController = controller;
      if (cameraController.value.isCaptureOrientationLocked) {
        await cameraController.unlockCaptureOrientation();
        showInSnackBar('Capture orientation unlocked');
      } else {
        await cameraController.lockCaptureOrientation();
        showInSnackBar(
            'Capture orientation locked to ${cameraController.value.lockedCaptureOrientation.toString().split('.').last}');
      }
    }
  }

  void onSetFlashModeButtonPressed(FlashMode mode) {
    setFlashMode(mode).then((_) {
      if (mounted) setState(() {});
      showInSnackBar('Flash mode set to ${mode.toString().split('.').last}');
    });
  }

  void onSetExposureModeButtonPressed(ExposureMode mode) {
    setExposureMode(mode).then((_) {
      if (mounted) setState(() {});
      showInSnackBar('Exposure mode set to ${mode.toString().split('.').last}');
    });
  }

  void onSetFocusModeButtonPressed(FocusMode mode) {
    setFocusMode(mode).then((_) {
      if (mounted) setState(() {});
      showInSnackBar('Focus mode set to ${mode.toString().split('.').last}');
    });
  }

  void onVideoRecordButtonPressed() {
    startVideoRecording().then((_) {
      if (mounted) setState(() {});
    });
  }

  void onStopButtonPressed() {
    stopVideoRecording().then((file) {
      if (mounted) setState(() {});
      if (file != null) {
        showInSnackBar('Video recorded to ${file.path}');
        videoFile = file;
        _startVideoPlayer();
      }
    });
  }

  void onPauseButtonPressed() {
    pauseVideoRecording().then((_) {
      if (mounted) setState(() {});
      showInSnackBar('Video recording paused');
    });
  }

  void onResumeButtonPressed() {
    resumeVideoRecording().then((_) {
      if (mounted) setState(() {});
      showInSnackBar('Video recording resumed');
    });
  }

  Future<void> startVideoRecording() async {
    final CameraController cameraController = controller;

    if (cameraController == null || !cameraController.value.isInitialized) {
      showInSnackBar('Error: select a camera first.');
      return;
    }

    if (cameraController.value.isRecordingVideo) {
      // A recording is already started, do nothing.
      return;
    }

    try {
      await cameraController.startVideoRecording();
    } on CameraException catch (e) {
      _showCameraException(e);
      return;
    }
  }

  Future<XFile> stopVideoRecording() async {
    final CameraController cameraController = controller;

    if (cameraController == null || !cameraController.value.isRecordingVideo) {
      return null;
    }

    try {
      return cameraController.stopVideoRecording();
    } on CameraException catch (e) {
      _showCameraException(e);
      return null;
    }
  }

  Future<void> pauseVideoRecording() async {
    final CameraController cameraController = controller;

    if (cameraController == null || !cameraController.value.isRecordingVideo) {
      return null;
    }

    try {
      await cameraController.pauseVideoRecording();
    } on CameraException catch (e) {
      _showCameraException(e);
      rethrow;
    }
  }

  Future<void> resumeVideoRecording() async {
    final CameraController cameraController = controller;

    if (cameraController == null || !cameraController.value.isRecordingVideo) {
      return null;
    }

    try {
      await cameraController.resumeVideoRecording();
    } on CameraException catch (e) {
      _showCameraException(e);
      rethrow;
    }
  }

  Future<void> setFlashMode(FlashMode mode) async {
    if (controller == null) {
      return;
    }

    try {
      await controller.setFlashMode(mode);
    } on CameraException catch (e) {
      _showCameraException(e);
      rethrow;
    }
  }

  Future<void> setExposureMode(ExposureMode mode) async {
    if (controller == null) {
      return;
    }

    try {
      await controller.setExposureMode(mode);
    } on CameraException catch (e) {
      _showCameraException(e);
      rethrow;
    }
  }

  Future<void> setExposureOffset(double offset) async {
    if (controller == null) {
      return;
    }

    setState(() {
      _currentExposureOffset = offset;
    });
    try {
      offset = await controller.setExposureOffset(offset);
    } on CameraException catch (e) {
      _showCameraException(e);
      rethrow;
    }
  }

  Future<void> setFocusMode(FocusMode mode) async {
    if (controller == null) {
      return;
    }

    try {
      await controller.setFocusMode(mode);
    } on CameraException catch (e) {
      _showCameraException(e);
      rethrow;
    }
  }

  Future<void> _startVideoPlayer() async {
    if (videoFile == null) {
      return;
    }

    final VideoPlayerController vController =
    VideoPlayerController.file(File(videoFile.path));
    videoPlayerListener = () {
      if (videoController != null && videoController.value.size != null) {
        // Refreshing the state to update video player with the correct ratio.
        if (mounted) setState(() {});
        videoController.removeListener(videoPlayerListener);
      }
    };
    vController.addListener(videoPlayerListener);
    await vController.setLooping(true);
    await vController.initialize();
    await videoController.dispose();
    if (mounted) {
      setState(() {
        imageFile = null;
        videoController = vController;
      });
    }
    await vController.play();
  }

  Future<XFile> takePicture() async {
    final CameraController cameraController = controller;
    if (cameraController == null || !cameraController.value.isInitialized) {
      showInSnackBar('Error: select a camera first.');
      return null;
    }

    if (cameraController.value.isTakingPicture) {
      // A capture is already pending, do nothing.
      return null;
    }

    try {
      XFile file = await cameraController.takePicture();
      return file;
    } on CameraException catch (e) {
      _showCameraException(e);
      return null;
    }
  }

  void _showCameraException(CameraException e) {
    logError(e.code, e.description);
    showInSnackBar('Error: ${e.code}\n${e.description}');
  }
}

class CameraApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CameraExampleHome(),
    );
  }
}

List<CameraDescription> cameras = [];

Future<void> main() async {
  // Fetch the available cameras before initializing the app.
  try {
    WidgetsFlutterBinding.ensureInitialized();
    cameras = await availableCameras();
  } on CameraException catch (e) {
    logError(e.code, e.description);
  }
  runApp(CameraApp());
}

This sample is a direct copy of https://github.com/flutter/plugins/blob/master/packages/camera/camera/example/lib/main.dart

This copy removes ALL null-safety features implemented which restricted the code from working on flutter versions < 2

The camera package version must be lower than 0.8.0

Tested on flutter version 1.22.6 and camera package version 0.7.0

Not sure why extra code is needed in the initState() function but my best guess is some null safety took care of that initialisation implicitly.

Official plugin page: https://pub.dev/packages/camera