how to cancel camera auto-focus

[Gotta-C]

I tried to set parameter in CameraPreferencesActivity.java，but not work. I think the camera is continus focusing when it moves，that causes image blur and the tracking points is not confidence, so the pose translation is not perfect.
Camera.Parameters params = cam.getParameters()
params.setFocusMode(Camera.Parameters.FOCUS_MODE_FIXED);
cam.setParameters(params);