无法恢复查看寻呼机片段状态

Question

我有一个带有 3 个片段的视图寻呼机。我第一次使用改造 rest api 填充我的每个片段。我想要实现的是当用户在第一个或第三个片段中向后滑动时（这两个片段正在被视图寻呼机破坏）以恢复数据（保存在数组列表中）并且不再进行休息 api 调用.我所做的是将下载数据的数组列表保存在 onSaveInstanceState() 中，并在用户第一次滑回上述 2 个片段之一时成功检索它。问题是当我导航回两个片段中的任何一个片段时，保存数组列表的特定捆绑键包含空值。

CompletedSurveysFragment(第三个片段)：

public class CompletedSurveysFragment extends Fragment implements SAMVCView {

    private static final String debugTag = CompletedSurveysFragment.class.getSimpleName();
    private View view;
    private RecyclerView completedSurveysRcV;
    private SAMVCPresenterImpl SAMVCpresenterImpl;
    private SurveysRcvAdapter surveysRcvAdapter;
    private List<SurveyData> data;

    public CompletedSurveysFragment() {}

    public static CompletedSurveysFragment newInstance() {
        return new CompletedSurveysFragment();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.e(debugTag, "onCreateView");
        if ( view == null ) view = inflater.inflate(R.layout.fragment_completedsurveys, container, false);
        completedSurveysRcV = (RecyclerView) view.findViewById(R.id.completedSurveysRcV);
        return view;
    }

    // TODO: 21/6/2016 configure Limit and offset values
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.e(debugTag, "onActivityCreated " + savedInstanceState);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
        completedSurveysRcV.setHasFixedSize(true);
        completedSurveysRcV.setLayoutManager(linearLayoutManager);
        completedSurveysRcV.addItemDecoration(new DividerItemDecoration(ContextCompat.getDrawable(getActivity(), R.drawable.divider)));
        if (savedInstanceState == null) {
            SAMVCpresenterImpl = new SAMVCPresenterImpl(this);
            SAMVCpresenterImpl.getSurveysBasedOnSpecificFirmId(new AllSurveysBody(getResources().getString(R.string.list_surveys), LoginActivity.getSessionPrefs(getActivity()).getInt(getResources().getString(R.string.firm_id), 0), getResources().getString(R.string.completed), 8, 0));

            surveysRcvAdapter = new SurveysRcvAdapter(null, completedSurveysRcV);
            completedSurveysRcV.setAdapter(surveysRcvAdapter);
        } else {
            //Log.e(debugTag, savedInstanceState.+"");
            if (savedInstanceState.getParcelableArrayList("data") != null) {
                Log.e(debugTag, "here "+ savedInstanceState);
                surveysRcvAdapter = new SurveysRcvAdapter(savedInstanceState.<SurveyData>getParcelableArrayList("data"), completedSurveysRcV);
                completedSurveysRcV.setAdapter(surveysRcvAdapter);
                surveysRcvAdapter.notifyDataSetChanged();
            }
            //Log.e(debugTag, getArguments().getParcelableArrayList("data")+"");
        }
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putParcelableArrayList("data", (ArrayList<? extends Parcelable>) this.data);
        Log.e(debugTag, "CompletedFragment onSaveInstanceState "+ outState);
    }

    @Override
    public void onSuccessSurveysFetched(List<SurveyData> data) {
        this.data = data;
        surveysRcvAdapter = new SurveysRcvAdapter(data, completedSurveysRcV);
        completedSurveysRcV.setAdapter(surveysRcvAdapter);
        surveysRcvAdapter.notifyDataSetChanged();
    }

    @Override
    public void onFailure() {

    }
}

查看寻呼机适配器：

public class SurveysPagerAdapter extends FragmentStatePagerAdapter {

    private static final String debugTag = SurveysPagerAdapter.class.getSimpleName();
    private List<SurveyData> data;
    String[] tabText;

    public SurveysPagerAdapter(FragmentManager fragmentManager, String[] tabText) {
        super(fragmentManager);
        this.tabText = tabText;
    }

    @Override
    public Fragment getItem(int position) {
        Log.e("SurveysPagerAdapter", position+"");
        switch (position) {
            case 0:
                return CompletedSurveysFragment.newInstance();
            case 1:
                return OngoingSurveysFragment.newInstance();
            case 2:
                return PendingSurveysFragment.newInstance();
            default:
                return null;
        }
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabText[position];
    }

    @Override
    public int getCount() {
        return 3;
    }
}

Answer 1

您的问题是您总是返回片段的新实例。不要在每次用户滑动时调用CompletedSurveysFragment.newInstance();（和您的其他片段），而是创建一个片段数组并以这种方式检索它：

    ...
    Fragment [] pages = new Fragment[getCount()];
    ...
     @Override
        public Fragment getItem(int position) {
            Log.e("SurveysPagerAdapter", position+"");
    switch (position) {
                case 0:
                    if(pages[position] == null)
                        pages[position] =  CompletedSurveysFragment.newInstance();
                    return pages[position];
    ...
    }

然后，您可以在onCreate() 中获取和缓存您的数据，然后在您各自的片段中的onResume() 中检索它。

Answer 2

我认为onPause() 和onResume() 不会工作。片段与其父活动相关联，因此由于您浏览片段，父活动处于onResume() 状态。我建议你做的是使用单例对象来获取和存储你的数据。每个片段都可以保留对相应对象的引用，并可以即时访问您需要的数据。有很多关于单例模式及其工作原理的信息。

Answer 3

发生这种情况的原因是 onSaveInstanceState 仅在父活动关闭时发生。由于在片段之间切换时，viewpager 的父 Activity 仍然处于活动状态，因此不会调用 onSaveInstanceState。

要按您的意愿保存数据，我可能会做的是将数据保存在onPause() 中并检索onResume() 中的数据。

编辑

根据docs，修改Bundle后需要调用super.onSaveInstanceState(savedInstanceState);。

    @Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    // Save the user's current game state
    savedInstanceState.putInt(STATE_SCORE, mCurrentScore);
    savedInstanceState.putInt(STATE_LEVEL, mCurrentLevel);

    // Always call the superclass so it can save the view hierarchy state
    super.onSaveInstanceState(savedInstanceState);
}