Mobile Vision API fix for missing autofocus feature

VisionApiFocusFix.java

/*
 * IF YOU WANT TO JUST ACCESS THE CAMERA INSTANCE SO THAT YOU CAN SET ANY OF THE PARAMETERS, VISIT THE FOLLOWING LINK:
 * https://gist.github.com/Gericop/364dd12b105fdc28a0b6
 */

/**
 * <p>
 * Sets the Mobile Vision API provided {@link com.google.android.gms.vision.CameraSource}'s
 * focus mode. Use {@link Camera.Parameters#FOCUS_MODE_CONTINUOUS_PICTURE} or
 * {@link Camera.Parameters#FOCUS_MODE_CONTINUOUS_VIDEO} for continuous autofocus.
 * </p>
 * <p>
 * Note that the CameraSource's {@link CameraSource#start()} or
 * {@link CameraSource#start(SurfaceHolder)} has to be called and the camera image has to be
 * showing prior using this method as the CameraSource only creates the camera after calling
 * one of those methods and the camera is not available immediately. You could implement some
 * kind of a callback method for the SurfaceHolder that notifies you when the imaging is ready
 * or use a direct action (e.g. button press) to set the focus mode.
 * </p>
 * <p>
 * Check out <a href="https://github.com/googlesamples/android-vision/blob/master/face/multi-tracker/app/src/main/java/com/google/android/gms/samples/vision/face/multitracker/ui/camera/CameraSourcePreview.java#L84">CameraSourcePreview.java</a>
 * which contains the method <code>startIfReady()</code> that has the following line:
 * <blockquote><code>mCameraSource.start(mSurfaceView.getHolder());</code></blockquote><br>
 * After this call you can use our <code>cameraFocus(...)</code> method because the camera is ready.
 * </p>
 *
 * @param cameraSource The CameraSource built with {@link com.google.android.gms.vision.CameraSource.Builder}.
 * @param focusMode    The focus mode. See {@link android.hardware.Camera.Parameters} for possible values.
 * @return true if the camera's focus is set; false otherwise.
 * @see com.google.android.gms.vision.CameraSource
 * @see android.hardware.Camera.Parameters
 */
public static boolean cameraFocus(@NonNull CameraSource cameraSource, @NonNull String focusMode) {
    Field[] declaredFields = CameraSource.class.getDeclaredFields();

    for (Field field : declaredFields) {
        if (field.getType() == Camera.class) {
            field.setAccessible(true);
            try {
                Camera camera = (Camera) field.get(cameraSource);
                if (camera != null) {
                    Camera.Parameters params = camera.getParameters();
                    params.setFocusMode(focusMode);
                    camera.setParameters(params);
                    return true;
                }

                return false;
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }

            break;
        }
    }

    return false;
}