TakePicturePreview示例

以下是一个使用 Camera2 API 实现 TakePicturePreview 功能的示例代码：

1. 在布局文件中添加一个 TextureView 控件用于显示相机预览：

<TextureView
    android:id="@+id/texture_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

2. 在 Activity 中初始化 Camera2 API：

private CameraManager mCameraManager;
private String mCameraId;
private CameraDevice mCameraDevice;
private CaptureRequest.Builder mPreviewRequestBuilder;
private CameraCaptureSession mCaptureSession;
private Size mPreviewSize;
private ImageReader mImageReader;

private void initCamera() {
    mCameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        // 获取可用的摄像头列表
        String[] cameraIds = mCameraManager.getCameraIdList();
        for (String cameraId : cameraIds) {
            // 获取摄像头的特性
            CameraCharacteristics characteristics = mCameraManager.getCameraCharacteristics(cameraId);
            // 判断是否为后置摄像头
            if (characteristics.get(CameraCharacteristics.LENS_FACING) == CameraCharacteristics.LENS_FACING_BACK) {
                mCameraId = cameraId;
                break;
            }
        }
        // 打开相机
        mCameraManager.openCamera(mCameraId, mCameraStateCallback, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

3. 在 CameraDevice.StateCallback 中获取相机预览尺寸并设置预览界面：

private CameraDevice.StateCallback mCameraStateCallback = new CameraDevice.StateCallback() {
    @Override
    public void onOpened(@NonNull CameraDevice camera) {
        mCameraDevice = camera;
        try {
            // 获取相机预览尺寸
            StreamConfigurationMap map = mCameraManager.getCameraCharacteristics(mCameraId)
                    .get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            mPreviewSize = getOptimalPreviewSize(map.getOutputSizes(SurfaceTexture.class), mTextureView.getWidth(), mTextureView.getHeight());
            // 设置预览界面
            SurfaceTexture surfaceTexture = mTextureView.getSurfaceTexture();
            surfaceTexture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
            Surface previewSurface = new Surface(surfaceTexture);
            mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            mPreviewRequestBuilder.addTarget(previewSurface);
            // 创建 ImageReader 用于拍照
            mImageReader = ImageReader.newInstance(mPreviewSize.getWidth(), mPreviewSize.getHeight(), ImageFormat.JPEG, 1);
            mImageReader.setOnImageAvailableListener(mOnImageAvailableListener, null);
            // 打开相机预览
            mCameraDevice.createCaptureSession(Arrays.asList(previewSurface, mImageReader.getSurface()), mSessionStateCallback, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

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

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

private Size getOptimalPreviewSize(Size[] sizes, int width, int height) {
    List<Size> sizeList = new ArrayList<>();
    for (Size size : sizes) {
        if (size.getWidth() <= width && size.getHeight() <= height) {
            sizeList.add(size);
        }
    }
    if (sizeList.isEmpty()) {
        return sizes[0];
    }
    Size[] sizeArray = new Size[sizeList.size()];
    sizeList.toArray(sizeArray);
    return Collections.max(Arrays.asList(sizeArray), new CompareSizesByArea());
}

4. 在 CameraCaptureSession.StateCallback 中启动相机预览：

private CameraCaptureSession.StateCallback mSessionStateCallback = new CameraCaptureSession.StateCallback() {
    @Override
    public void onConfigured(@NonNull CameraCaptureSession session) {
        mCaptureSession = session;
        try {
            // 自动对焦
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            // 打开闪光灯
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
            // 设置预览帧率
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_TARGET_FPS_RANGE, new Range<Integer>(30, 30));
            // 开始预览
            mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onConfigureFailed(@NonNull CameraCaptureSession session) {

    }
};

5. 在 ImageReader.OnImageAvailableListener 中保存拍照图片并显示预览：

private ImageReader.OnImageAvailableListener mOnImageAvailableListener = new ImageReader.OnImageAvailableListener() {
    @Override
    public void onImageAvailable(ImageReader reader) {
        try {
            // 保存拍照图片
            Image image = reader.acquireLatestImage();
            ByteBuffer buffer = image.getPlanes()[0].getBuffer();
            byte[] data = new byte[buffer.remaining()];
            buffer.get(data);
            File pictureFile = new File(getExternalFilesDir(null), "picture.jpg");
            FileOutputStream outputStream = new FileOutputStream(pictureFile);
            outputStream.write(data);
            outputStream.close();
            // 显示预览
            Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
            mTextureView.setImageBitmap(bitmap);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
};

在用户拍照后，可以在相应的按钮点击事件中调用 mCaptureSession.capture 方法拍照并保存图片。在保存图片之后，需要使用 startActivityForResult 方法启动另一个 Activity，并将图片路径返回给调用方。