Android 相机无法从后台服务拍照

Question

我已经实现了一项从后台线程拍摄照片的服务，但照片从未在我的任何设备上拍摄过......这是代码(下面的日志输出):

public class PhotoCaptureService extends Service {
    private static final String TAG = "PhotoCaptureService";

    @Override
    public void onStart(Intent intent, int startId) {
        super.onStart(intent, startId);
        Log.d(TAG, "Starting the PhotoCaptureService");
        takePhoto();
    }

    private void takePhoto() {

        Log.d(TAG, "Preparing to take photo");
        Camera camera = null;

        try {

            camera = Camera.open();

        } catch (RuntimeException e) {

            Log.e(TAG, "Camera not available", e);
            return;
        }

        if (null == camera) {

            Log.e(TAG, "Could not get camera instance");
            return;
        }

        Log.d(TAG, "Got the camera, creating the dummy surface texture");
        SurfaceTexture dummySurfaceTexture = new SurfaceTexture(0);

        try {

            camera.setPreviewTexture(dummySurfaceTexture);

        } catch (Exception e) {

            Log.e(TAG, "Could not set the surface preview texture", e);
        }

        Log.d(TAG, "Preview texture set, starting preview");

        camera.startPreview();

        Log.d(TAG, "Preview started");

        camera.takePicture(null, null, new Camera.PictureCallback() {

            @Override
            public void onPictureTaken(byte[] data, Camera camera) {

                Log.d(TAG, "Photo taken, stopping preview");

                camera.stopPreview();

                Log.d(TAG, "Preview stopped, releasing camera");

                camera.release();

                Log.d(TAG, "Camera released");
            }
        });
    }

记录输出:

D/PhotoCaptureService﹕ Starting the PhotoCaptureService
D/PhotoCaptureService﹕ Preparing to take photo
D/PhotoCaptureService﹕ Got the camera, creating the dummy surface texture
D/PhotoCaptureService﹕ Preview texture set, starting preview
D/PhotoCaptureService﹕ Preview started

此时没有其他事情发生，永远不会调用 onPictureTaken 方法，也不会抛出任何错误或异常。有谁知道为什么会这样？我查看了 StackOverflow 上的所有相机教程，但似乎没有任何效果。

Answer 1

根据我的经验和阅读的内容，虚拟 SurfaceTexture 策略并不适用于所有手机。尝试添加一个 1x1 像素的 SurfaceView 并在 SurfaceView.getHolder() 的 onSurfaceCreated 回调中开始预览(通过 addCallback 添加)。

参见 Taking picture from camera without preview获取更多信息。