protected void checkPreconditions(SurfaceControl sc) {
    sc.checkNotReleased();
}

private void checkNotReleased() {
    if (mNativeObject == 0) throw new NullPointerException(
            "Invalid " + this + ", mNativeObject is null. Have you called release() already?");
}

检查 SurfaceControl 的 mNativeObject 是否是非零。