Flutter Vision Camera

main.dart

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

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

class FlutterVisionHome extends StatefulWidget {
  @override
  _FlutterVisionHomeState createState() {
    return _FlutterVisionHomeState();
  }
}

void logError(String code, String message) =>
    print('Error: $code\nError Message: $message');

class _FlutterVisionHomeState extends State<FlutterVisionHome> {
  CameraController controller;
  String imagePath;

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

  @override
  void initState() {
    super.initState();
    controller = CameraController(cameras[0], ResolutionPreset.medium);
    controller.initialize().then((_) {
      if (!mounted) {
        return;
      }
      setState(() {});
    });
  }

  @override
  void dispose() {
    controller?.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: const Text('Flutter Vision'),
      ),
      body: Column(
        children: <Widget>[
          Expanded(
            child: Container(
              child: Padding(
                padding: const EdgeInsets.all(1.0),
                child: Center(
                  child: _cameraPreviewWidget(),
                ),
              ),
            ),
          ),
          _captureControlRowWidget(),
        ],
      ),
    );
  }

  /// Display the preview from the camera (or a message if the preview is not available).
  Widget _cameraPreviewWidget() {
    if (controller == null || !controller.value.isInitialized) {
      return const Text(
        'Tap a camera',
        style: TextStyle(
          color: Colors.white,
          fontSize: 24.0,
          fontWeight: FontWeight.w900,
        ),
      );
    } else {
      return AspectRatio(
        aspectRatio: controller.value.aspectRatio,
        child: CameraPreview(controller),
      );
    }
  }

  /// Display the control bar with buttons to take pictures.
  Widget _captureControlRowWidget() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      mainAxisSize: MainAxisSize.max,
      children: <Widget>[
        IconButton(
          icon: const Icon(Icons.camera_alt),
          color: Colors.blue,
          onPressed: controller != null &&
                  controller.value.isInitialized 
              ? onTakePictureButtonPressed
              : null,
        )
      ],
    );
  }

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

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

  void onTakePictureButtonPressed() {
    takePicture().then((String filePath) {
      if (mounted) {
        setState(() {
          imagePath = filePath;
        });
        if (filePath != null) showInSnackBar('Picture saved to $filePath');
      }
    });
  }

  Future<String> takePicture() async {
    if (!controller.value.isInitialized) {
      showInSnackBar('Error: select a camera first.');
      return null;
    }
    final Directory extDir = await getApplicationDocumentsDirectory();
    final String dirPath = '${extDir.path}/Pictures/flutter_vision';
    await Directory(dirPath).create(recursive: true);
    final String filePath = '$dirPath/${timestamp()}.jpg';

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

    try {
      await controller.takePicture(filePath);
    } on CameraException catch (e) {
      _showCameraException(e);
      return null;
    }
    return filePath;
  }

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

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

List<CameraDescription> cameras;

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

when i run the app, i get an exception 'ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.
' with _stacktrace
( defaultBinaryMessenger. (package:flutter/src/services/binary_messenger.dart:93:7)
#1 defaultBinaryMessenger (package:flutter/src/services/binary_messenger.dart:106:4)
#2 MethodChannel.binaryMessenger (package:flutter/src/services/platform_channel.dart:145:62)
#3 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:151:35)
#4 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:334:12)
#5 MethodChannel.invokeListMethod (package:flutter/src/services/platform_channel.dart:347:40)
#6 availableCameras (package:camera/camera.dart:81:10)
#7 main (package:camer_detect/main.dart:165:21)
#8 _runMainZoned.. (dart:ui/hooks.dart:233:25)
#9 _rootRun (dart:async/zone.dart:1190:13)
#10 _CustomZone.run (dart:async/zone.dart:1093:19)
#11 _runZoned (dart:async/zone.dart:1630:10)
#12 runZonedGuarded (dart:async/zone.dart:1618:12)
#13 _runMainZoned. (dart:ui/hooks.dart:225:5)
#14 _startIsolate. (dart:isolate-patch/isolate_patch.dart:301:19)
#15 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)
)