实现 camera2扫码功能

要实现 camera2 扫码功能，可以按照以下步骤进行操作：

1. 在 AndroidManifest.xml 中添加相机权限：

<uses-permission android:name="android.permission.CAMERA" />

2. 在布局文件中添加 SurfaceView 组件，用于显示相机预览：

<SurfaceView
    android:id="@+id/camera_preview"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

3. 在 Activity 中获取 SurfaceView 组件，并在 onResume() 方法中打开相机：

private SurfaceView mPreview;
private CameraManager mCameraManager;
private CameraDevice mCameraDevice;
private CameraCaptureSession mCaptureSession;
private CaptureRequest.Builder mPreviewRequestBuilder;
private HandlerThread mBackgroundThread;
private Handler mBackgroundHandler;

@Override
protected void onResume() {
    super.onResume();
    startBackgroundThread();

    mPreview = findViewById(R.id.camera_preview);
    SurfaceHolder holder = mPreview.getHolder();
    holder.addCallback(new SurfaceHolder.Callback() {
        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            openCamera();
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
            // do nothing
        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            closeCamera();
        }
    });
}

private void startBackgroundThread() {
    mBackgroundThread = new HandlerThread("CameraBackground");
    mBackgroundThread.start();
    mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}

private void openCamera() {
    mCameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        String cameraId = mCameraManager.getCameraIdList()[0];
        mCameraManager.openCamera(cameraId, new CameraDevice.StateCallback() {
            @Override
            public void onOpened(CameraDevice camera) {
                mCameraDevice = camera;
                createCameraPreviewSession();
            }

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

            @Override
            public void onError(CameraDevice camera, int error) {
                camera.close();
                mCameraDevice = null;
            }
        }, mBackgroundHandler);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

private void closeCamera() {
    if (mCaptureSession != null) {
        mCaptureSession.close();
        mCaptureSession = null;
    }
    if (mCameraDevice != null) {
        mCameraDevice.close();
        mCameraDevice = null;
    }
}

private void createCameraPreviewSession() {
    try {
        Surface surface = mPreview.getHolder().getSurface();
        mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
        mPreviewRequestBuilder.addTarget(surface);
        mCameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
            @Override
            public void onConfigured(CameraCaptureSession session) {
                if (mCameraDevice == null) {
                    return;
                }
                mCaptureSession = session;
                try {
                    mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                    mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(), null, mBackgroundHandler);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onConfigureFailed(CameraCaptureSession session) {
                // do nothing
            }
        }, mBackgroundHandler);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

4. 添加扫码功能，可以使用 zxing 库，将其添加到项目的依赖中：

dependencies {
    implementation 'com.google.zxing:core:3.4.1'
}

5. 在 Activity 中添加扫码方法：

private static final int REQUEST_CODE_SCAN = 0x0000;

private void startScan() {
    Intent intent = new Intent(this, CaptureActivity.class);
    startActivityForResult(intent, REQUEST_CODE_SCAN);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == REQUEST_CODE_SCAN && resultCode == RESULT_OK) {
        String result = data.getStringExtra(CaptureActivity.EXTRA_RESULT);
        // do something with the scan result
    } else {
        super.onActivityResult(requestCode, resultCode, data);
    }
}

6. 在扫码界面中启动相机，并在扫描到二维码时返回结果：

private SurfaceView mPreview;
private Camera mCamera;
private Handler mHandler;
private boolean mIsScanning = false;

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

    mHandler = new Handler();

    mPreview = findViewById(R.id.camera_preview);
    SurfaceHolder holder = mPreview.getHolder();
    holder.addCallback(new SurfaceHolder.Callback() {
        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            startCamera();
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
            // do nothing
        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            stopCamera();
        }
    });
}

private void startCamera() {
    try {
        mCamera = Camera.open();
        Camera.Parameters params = mCamera.getParameters();
        params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
        mCamera.setParameters(params);
        mCamera.setPreviewDisplay(mPreview.getHolder());
        mCamera.setPreviewCallback(new Camera.PreviewCallback() {
            @Override
            public void onPreviewFrame(byte[] data, Camera camera) {
                if (mIsScanning) {
                    Camera.Size size = camera.getParameters().getPreviewSize();
                    int width = size.width;
                    int height = size.height;
                    Image barcode = new Image(width, height, "Y800");
                    barcode.setData(data);
                    Result result = new MultiFormatReader().decode(new BinaryBitmap(new HybridBinarizer(barcode)));
                    if (result != null) {
                        mIsScanning = false;
                        Intent intent = new Intent();
                        intent.putExtra(EXTRA_RESULT, result.getText());
                        setResult(RESULT_OK, intent);
                        finish();
                    }
                }
            }
        });
        mCamera.startPreview();
        mIsScanning = true;
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private void stopCamera() {
    if (mCamera != null) {
        mCamera.setPreviewCallback(null);
        mCamera.stopPreview();
        mCamera.release();
        mCamera = null;
    }
}

这样，就可以实现 camera2 扫码功能了。