Android camera2实现手动对焦

在Android Camera2 API中实现手动对焦需要以下步骤：

1. 获取CameraManager实例，使用该实例获取可用的相机设备列表。

2. 获取要使用的相机设备的CameraDevice实例。

3. 创建一个CaptureRequest.Builder对象，并将其与相机设备关联。

4. 设置手动对焦模式和对焦区域。

5. 构建CaptureRequest对象。

6. 启动相机预览。

7. 实现一个触摸事件监听器，在用户触摸屏幕时获取焦点坐标，并设置对焦区域。

8. 在触摸事件监听器中调用CaptureRequest.Builder.set(CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_START)触发对焦操作。

9. 实现一个CameraCaptureSession.CaptureCallback回调函数，在对焦完成后更新预览界面。

下面是一个简单的实现示例：

private void setupCamera() {
    // 获取相机管理器实例
    CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        // 获取可用的相机设备列表
        String[] cameraIds = cameraManager.getCameraIdList();
        for (String cameraId : cameraIds) {
            // 获取相机设备实例
            CameraDevice cameraDevice = cameraManager.openCamera(cameraId, mStateCallback, mBackgroundHandler);
            // 创建一个CaptureRequest.Builder对象，并将其与相机设备关联
            mPreviewRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            // 设置手动对焦模式和对焦区域
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_AUTO);
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_REGIONS, new MeteringRectangle[]{new MeteringRectangle(focusRect, 1000)});
            // 构建CaptureRequest对象
            mPreviewRequest = mPreviewRequestBuilder.build();
            // 启动相机预览
            cameraDevice.createCaptureSession(Arrays.asList(mSurface), mSessionCallback, mBackgroundHandler);
        }
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

private void startPreview() {
    try {
        // 设置自动对焦模式
        mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_AUTO);
        // 启动预览
        mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(), mCaptureCallback, mBackgroundHandler);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

private void setFocusArea(float x, float y) {
    // 计算对焦区域
    Rect focusRect = calculateFocusRect(x, y);
    // 设置对焦区域
    mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_REGIONS, new MeteringRectangle[]{new MeteringRectangle(focusRect, 1000)});
    // 触发对焦操作
    mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_START);
    try {
        // 更新预览界面
        mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(), mCaptureCallback, mBackgroundHandler);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

private CameraCaptureSession.CaptureCallback mCaptureCallback = new CameraCaptureSession.CaptureCallback() {
    @Override
    public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
        super.onCaptureCompleted(session, request, result);
        // 对焦完成后更新预览界面
        if (request.get(CaptureRequest.CONTROL_AF_TRIGGER) != null && request.get(CaptureRequest.CONTROL_AF_TRIGGER) == CameraMetadata.CONTROL_AF_TRIGGER_START) {
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, null);
            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            try {
                mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(), null, mBackgroundHandler);
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }
        }
    }
};

private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
    @Override
    public void onOpened(@NonNull CameraDevice camera) {
        mCameraDevice = camera;
        startPreview();
    }

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

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

private CameraCaptureSession.StateCallback mSessionCallback = new CameraCaptureSession.StateCallback() {
    @Override
    public void onConfigured(@NonNull CameraCaptureSession session) {
        mCaptureSession = session;
        try {
            mCaptureSession.setRepeatingRequest(mPreviewRequest, mCaptureCallback, mBackgroundHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onConfigureFailed(@NonNull CameraCaptureSession session) {
        session.close();
        mCaptureSession = null;
    }
};

在以上代码中，calculateFocusRect()方法用于计算对焦区域，可以根据需要自行实现。