等待从Callable返回回调数据

Question

我遇到了问题，我希望捕获预览并将其作为Callable的结果返回...

    package ro.ubbcluj.digitrecognitionapp;

    import java.io.ByteArrayOutputStream;
    import java.util.concurrent.Callable;
    import java.util.concurrent.CountDownLatch;

    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.graphics.Rect;
    import android.graphics.YuvImage;
    import android.hardware.Camera;
    import android.hardware.Camera.PreviewCallback;
    import android.util.Log;

    public class CameraCapturingTask implements Callable<Bitmap> {
    private Camera camera;
    private Bitmap imageBitmap;

    private CountDownLatch callBackFinished = new CountDownLatch(1);

    CameraCapturingTask(Camera camera) {
    this.camera = camera;
    }

    @Override
    public Bitmap call() throws Exception {
    Log.d("CapturePreviewTask", "Async Task started");
    try {
        camera.setOneShotPreviewCallback(pictureCallback);
        callBackFinished.await();                             // it blocks here!!!
    } catch (Exception e) {
        if (e instanceof InterruptedException) {
        Log.d("PreviewCapturingTask",
            "Task caught InterruptedException ,ok");
        }
    }
    return imageBitmap;
    }

    private PreviewCallback pictureCallback = new PreviewCallback() {
    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {
        Log.d("CameraPreview", "picture taken");
        getBitmap(data, camera);
        callBackFinished.countDown();
    }
    };

    private void getBitmap(byte[] data, Camera camera) {
    Log.d("Async Task", "Processing Image ");
    Camera.Parameters parameters = camera.getParameters();
    int width = parameters.getPreviewSize().width;
    int height = parameters.getPreviewSize().height;

    YuvImage yuv = new YuvImage(data, parameters.getPreviewFormat(), width,
        height, null);
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    yuv.compressToJpeg(new Rect(0, 0, width, height), 50, out);
    byte[] bytes = out.toByteArray();

    imageBitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
    }
  }

阻止我等待CountDownLatch ...如果我评论callBackFinished.await();，则在Thread返回后调用回调。

如何解决此问题并返回捕获预览的位图？