main.dart

  void main() async {
    WidgetsFlutterBinding.ensureInitialized();

    final cameras = await availableCameras();
    final firstCamera = cameras.first;

    runApp(
        DemoApp(firstCamera)
    );
  }

  class DemoApp extends StatelessWidget {
    final CameraDescription camera;
    const DemoApp(this.camera);

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        home: Scaffold(
          appBar: AppBar(
            title: const Text("Using camera"),
          ),
          body: TakePicture(
            camera: camera,
          ),
        ),

      );
    }

  }
  

take_picture.dart

  class TakePicture extends StatefulWidget {
    final CameraDescription camera;
    TakePicture({ required this.camera });

    @override
    _TakePictureState createState() => _TakePictureState();
  }

  class _TakePictureState extends State<TakePicture> {
    late final CameraController _controller;
    late final Future<void> _initController;

    @override
    void initState() {
      super.initState();
      _controller = CameraController(
        widget.camera,
        ResolutionPreset.high,
      );

      _initController = _controller.initialize();
    }

    @override
    void dispose() {
      _controller.dispose();
      super.dispose();
    }

    @override
    Widget build(BuildContext context) {
      return Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          FutureBuilder<void>(
            future: _initController,
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.done) {
                return Expanded(
                  child: Center(
                    child: AspectRatio(
                      aspectRatio: _controller.value.aspectRatio,
                      child: CameraPreview(_controller),
                    ),
                  ),
                );
              }

              return const Center(
                child: CircularProgressIndicator(),
              );
            },
          ),

          IconButton(
            icon: const Icon(Icons.photo_camera),
            onPressed: () => _takePhoto(context),
          )
        ],
      );
    }

    void _takePhoto(BuildContext context) async {
      await _initController;

      // File name and path
      final dir = await getTemporaryDirectory();
      final name = "mypic_${DateTime.now()}.png";

      // Store the picture at the given location
      final fullPath = path.join(dir.path, name);
      await _controller.takePicture(fullPath);

      Scaffold.of(context).showSnackBar(
          SnackBar(
            content: const Text("Picture taken!"),
            duration: const Duration(milliseconds: 600),
          )
      );
    }

  }