从RecyclerView中消失的数据

Question

I made an app with Fragment containing ViewPager. Inside that ViewPager I am displaying list using RecyclerView. When I launch app everything is great. But when I swipe few tabs and coming back list isn't shown. I don't know what is wrong...

Fragment displayed inside ViewPager

public class GradesFragmentPage extends Fragment {
    View view;
    List<Grade> gradeList;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.grades_page_fragment, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        BetterRecyclerView betterRecyclerView = (BetterRecyclerView) getActivity().findViewById(R.id.gradesRecycler);
        betterRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        this.view = view;

        if(getArguments() != null) {
            gradeList = getArguments().getParcelableArrayList("grades");

            BetterRecyclerView betterRecyclerView = (BetterRecyclerView) view.findViewById(R.id.gradesRecycler);
            betterRecyclerView.setAdapter(new GradesAdapter(getActivity(), gradeList));
        }
    }
}

BetterRecyclerView

public class BetterRecyclerView extends RecyclerView {
    public BetterRecyclerView(Context context) {
        super(context);
    }

    public BetterRecyclerView(Context context, AttributeSet attrs) {
        super(context,attrs);

        setLayoutManager(new LayoutManager() {
            @Override
            public LayoutParams generateDefaultLayoutParams() {
                return null;
            }
        });
    }

    public BetterRecyclerView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    //we need this protected method for scroll detection
    public int getVerticalScrollOffset() {
        return computeVerticalScrollOffset();
    }
}

Answer 1

ViewPager itself has a method setOffscreenPageLimit which allows you to specify number of pages kept by the adapter. So your fragments that are far away will be destroyed.

First of all looking at your code I don't see you doing any memory releasing measures in your fragments onDestroy(). The fact that fragment itself is destroyed and gc'ed does not mean all resources you allocated were removed too.

viewPager.setOffscreenPageLimit(10);