为什么PagerAdapter的restoreState()和saveState()不起作用？

Question

我试图ViewPager通过在其中实现两个方法来保存当前状态(当前位置等)PagerAdapter:restoreState()和saveState().但是,在我的情况下,它们似乎无法正常工作.我做错了什么？

@Override
public Parcelable saveState() {

Bundle bundle = new Bundle();
bundle.putParcelable("instanceState", super.saveState());
bundle.putInt("stateToSave", position);
return bundle;
}

@Override
public void restoreState(Parcelable state, ClassLoader c) {
if (state instanceof Bundle) {
  Bundle bundle = (Bundle) state;
  position = bundle.getInt("stateToSave");
  super.restoreState(bundle.getParcelable("instanceState"), c);
  return;
}
super.restoreState(state, c);
}