写一份完整的使用camera2扫描多张二维码并且每次扫描后打开闪光灯的代码

好的，以下是示例代码：

public class QRScannerActivity extends AppCompatActivity {

    // Camera-related variables
    private CameraManager cameraManager;
    private String cameraId;
    private CameraDevice cameraDevice;
    private CameraCaptureSession cameraCaptureSession;
    private CaptureRequest.Builder captureRequestBuilder;
    private ImageReader imageReader;

    // QR code-related variables
    private BarcodeDetector barcodeDetector;
    private boolean isScanning = false;

    // UI-related variables
    private TextureView textureView;
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_qrscanner);

        textureView = findViewById(R.id.texture_view);
        textView = findViewById(R.id.text_view);

        // Initialize barcode detector
        barcodeDetector = new BarcodeDetector.Builder(this)
                .setBarcodeFormats(Barcode.QR_CODE)
                .build();

        if (!barcodeDetector.isOperational()) {
            Toast.makeText(this, "Could not set up barcode detector", Toast.LENGTH_SHORT).show();
            finish();
        }

        // Set up texture view
        textureView.setSurfaceTextureListener(surfaceTextureListener);

        // Set up camera manager
        cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            cameraId = cameraManager.getCameraIdList()[0];
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private TextureView.SurfaceTextureListener surfaceTextureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
            // Open camera when texture view is available
            openCamera();
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
            // Do nothing
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
            closeCamera();
            return true;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surface) {
            // Do nothing
        }
    };

    private CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice camera) {
            cameraDevice = camera;
            createCameraPreviewSession();
        }

        @Override
        public void onDisconnected(CameraDevice camera) {
            cameraDevice.close();
            cameraDevice = null;
        }

        @Override
        public void onError(CameraDevice camera, int error) {
            cameraDevice.close();
            cameraDevice = null;
        }
    };

    private void openCamera() {
        try {
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA}, 1);
                return;
            }
            cameraManager.openCamera(cameraId, stateCallback, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void closeCamera() {
        if (cameraCaptureSession != null) {
            cameraCaptureSession.close();
            cameraCaptureSession = null;
        }
        if (cameraDevice != null) {
            cameraDevice.close();
            cameraDevice = null;
        }
        if (imageReader != null) {
            imageReader.close();
            imageReader = null;
        }
    }

    private void createCameraPreviewSession() {
        SurfaceTexture texture = textureView.getSurfaceTexture();
        texture.setDefaultBufferSize(textureView.getWidth(), textureView.getHeight());
        Surface surface = new Surface(texture);
        try {
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(surface);
            cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(CameraCaptureSession session) {
                    cameraCaptureSession = session;
                    try {
                        captureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                        cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
                    } catch (CameraAccessException e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onConfigureFailed(CameraCaptureSession session) {
                    Toast.makeText(QRScannerActivity.this, "Failed to create camera capture session", Toast.LENGTH_SHORT).show();
                }
            }, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
        @Override
        public void onImageAvailable(ImageReader reader) {
            Image image = reader.acquireLatestImage();
            if (image != null) {
                detectQRCode(image);
                image.close();
            }
        }
    };

    private void detectQRCode(Image image) {
        // Convert image to bitmap
        Bitmap bitmap = textureView.getBitmap(image.getWidth(), image.getHeight());

        // Rotate bitmap to correct orientation
        int rotation = getWindowManager().getDefaultDisplay().getRotation();
        Matrix matrix = new Matrix();
        matrix.postRotate(getRotationAngle(rotation, image.getWidth(), image.getHeight()));
        bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);

        // Detect QR code in bitmap
        Frame frame = new Frame.Builder().setBitmap(bitmap).build();
        SparseArray<Barcode> barcodes = barcodeDetector.detect(frame);
        if (barcodes.size() > 0) {
            String qrCode = barcodes.valueAt(0).rawValue;
            textView.setText(qrCode);
        }
    }

    private int getRotationAngle(int rotation, int width, int height) {
        int angle;
        switch (rotation) {
            case Surface.ROTATION_0:
                angle = 90;
                break;
            case Surface.ROTATION_90:
                angle = 0;
                break;
            case Surface.ROTATION_180:
                angle = 270;
                break;
            case Surface.ROTATION_270:
                angle = 180;
                break;
            default:
                angle = 0;
                break;
        }
        return (angle + getCameraOrientation()) % 360;
    }

    private int getCameraOrientation() {
        int orientation = 0;
        try {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
            orientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        return orientation;
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == 1) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                openCamera();
            } else {
                Toast.makeText(this, "Camera permission denied", Toast.LENGTH_SHORT).show();
                finish();
            }
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (textureView.isAvailable()) {
            openCamera();
        } else {
            textureView.setSurfaceTextureListener(surfaceTextureListener);
        }
    }

    @Override
    protected void onPause() {
        closeCamera();
        super.onPause();
    }

}

在这个示例代码中，我们使用了 Camera2 API 来打开摄像机，并且通过 TextureView 来显示摄像头捕获的图像。我们还使用了 Google 提供的 BarcodeDetector 来检测二维码。在检测到二维码后，我们将其文本值显示在 TextView 中。

对于每次扫描后打开闪光灯的功能，您可以在 detectQRCode 方法中添加以下代码：

if (barcodes.size() > 0) {
    String qrCode = barcodes.valueAt(0).rawValue;
    textView.setText(qrCode);

    // Open flash
    if (!isScanning) {
        captureRequestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_TORCH);
        try {
            cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        isScanning = true;
    }
}

在这个代码中，我们首先检查是否已经检测到了二维码。如果是，我们将文本显示在 TextView 中，并且检查是否已经开始了扫描。如果没有，我们将 captureRequestBuilder 中的 FLASH_MODE 设置为 FLASH_MODE_TORCH，并且使用 setRepeatingRequest 方法来打开闪光灯。最后，我们将 isScanning 设置为 true，表示已经开始了扫描。

注意，如果您希望在每次扫描后关闭闪光灯，您可以在 detectQRCode 方法中添加以下代码：

if (barcodes.size() > 0) {
    String qrCode = barcodes.valueAt(0).rawValue;
    textView.setText(qrCode);

    // Toggle flash
    if (!isScanning) {
        captureRequestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_TORCH);
        try {
            cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        isScanning = true;
    } else {
        captureRequestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
        try {
            cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        isScanning = false;
    }
}

在这个代码中，我们检查 isScanning 的值。如果是 false，我们将 FLASH_MODE 设置为 FLASH_MODE_TORCH 并且打开闪光灯。如果是 true，我们将 FLASH_MODE 设置为 FLASH_MODE_OFF 并且关闭闪光灯。最后，我们将 isScanning 的值取反，表示闪光灯的状态已经反转。