在第二次单击选项卡之前，Android片段不会加载数据

Question

我正在开发一个Android应用程序来跟踪咖啡消费，并且我有5个选项卡，如所附图像所示。在选项卡（片段）之一中，我有一个viewPager，用于在饼图中显示数据。我遇到一个奇怪的问题，当我第二次单击该片段时，仅显示数据。最初，它看起来像这样Pie chart on the first click。当我第二次单击时，它将添加信息。 Piechart on the second click。用于显示数据的软件包为https://github.com/PhilJay/MPAndroidChart。

我不确定这到底是哪里出了问题，但是我已经附上了TrackingFragment和一些CostFragment（片段中的片段）的代码。数据是从解析服务器客户端获取的，但我可以肯定的是问题在于片段的初始化。

感谢任何帮助。

TrackingFragment

  ERROR in src/app/service/liveLocation/live-location.service.ts(25,4): error TS2339: Property 'subscribe' does not exist on type 'Promise<any>'.

CostFragment

public class TrackingFragment extends Fragment {

private static ArrayList<String> drinkNames;
private static String TAG = "TrackingFragment";
CaffeineFragment caffeineFragment;
CostFragment costFragment;
QuantityFragment quantityFragment;

public TrackingFragment() {
    // Required empty public constructor
}


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

    costFragment = new CostFragment();
    caffeineFragment = new CaffeineFragment();
    quantityFragment = new QuantityFragment();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_tracking, container, false);

    ViewPager pager = view.findViewById(R.id.viewPager);

    initViewPager(pager);

    TabLayout tabLayout = view.findViewById(R.id.tabLayout);
    tabLayout.setupWithViewPager(pager);
    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
    tabLayout.setTabMode(TabLayout.MODE_FIXED);

    return view;
}

private void initViewPager(ViewPager pager) {

    FragmentAdapter adapter = new FragmentAdapter(getChildFragmentManager());

    adapter.addFragment(costFragment, "Price");
    adapter.addFragment(caffeineFragment, "Caffeine");
    adapter.addFragment(quantityFragment, "Quantity");
    pager.setAdapter(adapter);
    adapter.notifyDataSetChanged();
}


static class FragmentAdapter extends FragmentPagerAdapter{

    private final List<Fragment> fragmentList = new ArrayList<>();
    private final List<String> fragmentTitleList = new ArrayList<>();

    public FragmentAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
       return fragmentList.size();
    }


    public void addFragment(Fragment frag, String title){
        fragmentList.add(frag);
        fragmentTitleList.add(title);
    }

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        return fragmentTitleList.get(position);
    }
}

}

getParseInfo（）和addPieData（）

public class CostFragment extends Fragment {

private static final String TAG = "CostFragment";
public static ArrayList<Double> drinksPrice = new ArrayList<>();
public static ArrayList<String> drinksName = new ArrayList<>();
private PieChart piechart;
public static ArrayList<String> dates = new ArrayList<>();
private BarChart barchart;
private ArrayList<PieEntry> pieEntries = new ArrayList<>();
private ArrayList<BarEntry> barEntries = new ArrayList<>();


@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.tracking_layout_fragment, container, false);

    return view;
}


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

    Log.i(TAG, "onCreate: " + drinksPrice.toString());

    getPieData();
    getBarData();
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    piechart = view.findViewById(R.id.pieChart);
    barchart = view.findViewById(R.id.barChart);
    piechart.setRotationEnabled(true);

    getParseInfo();

    addBarData();
    addPieData();

}

Answer 1

将以下行从onViewCreated（）移到onCreateView（）：

piechart = view.findViewById(R.id.pieChart);
barchart = view.findViewById(R.id.barChart);
piechart.setRotationEnabled(true);

getParseInfo();

在那之后，在您的getParseInfo（）for循环之后，添加以下行：

parseQuery.findInBackground(new FindCallback<ParseObject>() {
    @Override
    public void done(List<ParseObject> objects, ParseException e) {
        if (e == null) 
         {
            for (ParseObject object : objects) {
                drinksSize.add(object.getInt("size"));
                drinksName.add(object.getString("itemName"));
                dates.add(getDate(object.getCreatedAt()));
            }
         getPieData();
         getBarData();
        }else{
            Log.i(TAG, "exception: " + e.getMessage());
        }
    }
});

之所以发生这种情况是因为，当您调用getParseInfo（）时，它将进入后台，并且在获得结果之前将调用getPieData（）。因此，为避免这种情况，请应用建议的更改。