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

List<CameraDescription>? cameras;

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();

  cameras = await availableCameras();
  runApp(CameraApp());
}

class CameraApp extends StatefulWidget {
  @override
  _CameraAppState createState() => _CameraAppState();
}

class _CameraAppState extends State<CameraApp>
    with WidgetsBindingObserver, TickerProviderStateMixin {
  CameraController? controller;

  @override
  void initState() {
    super.initState();
    controller = CameraController(cameras![0], ResolutionPreset.max);
    // WidgetsBinding.instance!.addObserver(this);
    _ambiguate(WidgetsBinding.instance)?.addObserver(this);
    controller!.initialize().then((_) {
      if (!mounted) {
        return;
      }
      setState(() {});
    });
  }

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

  void onNewCameraSelected(CameraDescription cameraDescription) async {
    if (controller != null) {
      await controller!.dispose();
    }

    final CameraController cameraController = CameraController(
      cameraDescription,
      ResolutionPreset.medium,
      enableAudio: true,
    );

    controller = cameraController;

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

    try {
      await cameraController.initialize();
    } on CameraException catch (e) {
      print(e);
    }

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

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    // App state changed before we got the chance to initialize.
    if (controller == null || !controller!.value.isInitialized) {
      return;
    }
    if (state == AppLifecycleState.inactive) {
      controller?.dispose();
    } else if (state == AppLifecycleState.resumed) {
      if (controller != null) {
        onNewCameraSelected(controller!.description);
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    if (!controller!.value.isInitialized) {
      return Container();
    }
    return MaterialApp(
      home: CameraPreview(controller!),
    );
  }
}

T? _ambiguate<T>(T? value) => value;

[✓] Flutter (Channel stable, 2.2.3, on macOS 11.5.1 20G80 darwin-x64, locale es-US)
    • Flutter version 2.2.3 at /Users/jesus_Herrera/development/flutter
    • Framework revision f4abaa0735 (2 months ago), 2021-07-01 12:46:11 -0700
    • Engine revision 241c87ad80
    • Dart version 2.13.4

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/jesus_Herrera/Library/Android/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/jesus_Herrera/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.5.1, Build version 12E507
    • CocoaPods version 1.10.0

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.60.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.26.0

[✓] Connected device (2 available)
    • M2006C3MG (mobile) • SGFMY9RCYPZXCMUO • android-arm    • Android 10 (API 29)
    • Chrome (web)       • chrome           • web-javascript • Google Chrome 93.0.4577.63

• No issues found!