Camera2 相机怎么预览

使用 Camera2 API 进行相机预览需要以下步骤：

1. 获取相机服务。

CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);

2. 获取相机 ID。

String cameraId = cameraManager.getCameraIdList()[0];

3. 打开相机。

cameraManager.openCamera(cameraId, new CameraDevice.StateCallback() {
    @Override
    public void onOpened(CameraDevice camera) {
        mCameraDevice = camera;
    }

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

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

4. 创建预览请求。

private void createPreviewSession() {
    try {
        SurfaceTexture texture = mTextureView.getSurfaceTexture();
        texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
        Surface surface = new Surface(texture);

        mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
        mPreviewRequestBuilder.addTarget(surface);

        mCameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
            @Override
            public void onConfigured(CameraCaptureSession session) {
                mCaptureSession = session;
                try {
                    mPreviewRequest = mPreviewRequestBuilder.build();
                    mCaptureSession.setRepeatingRequest(mPreviewRequest, null, null);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                }
            }

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

5. 开始预览。

private void startPreview() {
    try {
        createPreviewSession();
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

注意：以上代码仅供参考，具体实现可能需要根据实际需求进行修改。