using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Android;
using Android.App;
using Android.Content;
using Android.Content.PM;
using Android.Graphics;
using Android.Hardware.Camera2;
using Android.Media;
using Android.OS;
using Android.Provider;
using Android.Runtime;
using Android.Util;
using Android.Views;
using Android.Widget;


namespace Camera2BarcodeScanner
{
    public class CameraPreview : SurfaceView, ISurfaceHolderCallback
    {
        private CameraManager _cameraManager;
        private CameraDevice _cameraDevice;
        private CameraCaptureSession _captureSession;
        private CaptureRequest.Builder _previewBuilder;
        private Size _previewSize;
        private ImageReader _imageReader;
        private BarcodeDetector _barcodeDetector;
        private MainActivity _mainActivity;
        private CameraStateListener _stateListener;


        public CameraPreview(Context context, MainActivity mainActivity) : base(context)
        {
            _mainActivity = mainActivity;
            Holder.AddCallback(this);
            Holder.SetType(SurfaceType.PushBuffers);
            _stateListener = new CameraStateListener { OnDisconnectedAction = Stop };
            _barcodeDetector = new BarcodeDetector.Builder(context)
                .SetBarcodeFormats(BarcodeFormat.QrCode)
                .Build();
        }


        public void SurfaceCreated(ISurfaceHolder holder)
        {
            _cameraManager = (CameraManager)_mainActivity.GetSystemService(Context.CameraService);
            var cameraId = _mainActivity.GetCameraId(_cameraManager).Result;


            var cameraCharacteristics = _cameraManager.GetCameraCharacteristics(cameraId);
            var streamConfigurationMap = (StreamConfigurationMap)cameraCharacteristics.Get(CameraCharacteristics.ScalerStreamConfigurationMap);


            _previewSize = streamConfigurationMap.GetOutputSizes(SurfaceTexture.Class)[0];


            var permission = _mainActivity.CheckSelfPermission(Manifest.Permission.Camera);
            if (permission != Permission.Granted)
            {
                _mainActivity.RequestPermissions(new[] { Manifest.Permission.Camera }, 0);
                return;
            }


            _cameraManager.OpenCamera(cameraId, _stateListener, null);
        }


        public void SurfaceChanged(ISurfaceHolder holder, [GeneratedEnum] Format format, int width, int height)
        {
            // Do nothing
        }


        public void SurfaceDestroyed(ISurfaceHolder holder)
        {
            Stop();
        }


        private async Task StartPreview()
        {
            var surface = Holder.Surface;
            _previewBuilder = _cameraDevice.CreateCaptureRequest(CameraTemplate.Preview);
            _previewBuilder.AddTarget(surface);


            _imageReader = ImageReader.NewInstance(_previewSize.Width, _previewSize.Height, ImageFormatType.Jpeg, 2);
            _imageReader.SetOnImageAvailableListener(new Camera2ImageAvailableListener(_mainActivity), null);
            _previewBuilder.AddTarget(_imageReader.Surface);


            var outputs = new List<Surface> { surface, _imageReader.Surface };
            await _cameraDevice.CreateCaptureSessionAsync(outputs, new Camera2CaptureSessionListener(this), null);
        }


        public async void TakePicture()
        {
            if (_cameraDevice == null)
                return;


            _imageReader = ImageReader.NewInstance(_previewSize.Width, _previewSize.Height, ImageFormatType.Jpeg, 1);
            _imageReader.SetOnImageAvailableListener(new Camera2ImageAvailableListener(_mainActivity), null);


            var captureBuilder = _cameraDevice.CreateCaptureRequest(CameraTemplate.StillCapture);
            captureBuilder.AddTarget(_imageReader.Surface);


            var captureSessionListener = new Camera2CaptureSessionListener(this);
            await _cameraDevice.CreateCaptureSessionAsync(new List<Surface>


このコードは、SurfaceViewを使用してAndroidのカメラを起動し、プレビュー画像を表示し、バーコードスキャンを行うアプリケーションです。