启动画面使用AsyncTask

Question

I have a splash screen using AsyncTask , it will download some data from database and store the data in ArrayList . This ArrayList will be used for RecyclerView in fragments of MainActivity.class .

The problem is when I run the app from Android Studio to my phone, everything works perfectly. But, when I destroy the app and run it manually from my phone it will display blank white screen and then it will crash. And if I run once again after it crashed, the app will work. So, this app will always work only if I run it from Android Studio or after it crashed.

The error says that it is caused by the empty list. If I'm not mistaken, I think the AsyncTask doesn't seem to work properly after the activity is destroyed. But I don't know how to fix it. Please help me to solve this problem.

SplashScreen.java

public class SplashScreenActivity extends AppCompatActivity {
    public static Event event;
    private static List<Feed> feedList;
    private static List<Event> eventList;
    private static List<Event> todayList;
    private static List<Event> upcomingList;
    private static List<Partner> partnerList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_splashscreen);
        Time today = new Time(Time.getCurrentTimezone());
        today.setToNow();
        Config.TODAY_DATE = String.valueOf(today.monthDay) + "-" + String.valueOf(today.month) + "-" + String.valueOf(today.year);
        new DownloadData().execute("");
    }

    class DownloadData extends AsyncTask<String, Integer, String>
    {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            startActivity(new Intent(getBaseContext(), WelcomeActivity.class));
            finish();
        }

        @Override
        protected String doInBackground(String... params) {
            RequestHandler rh = new RequestHandler();
            String JSON_STRING = rh.sendGetRequest(Config.URL_GET_ALL_DATA);
            JSONObject jsonObject;
            eventList       = new ArrayList<>();
            todayList       = new ArrayList<>();
            upcomingList    = new ArrayList<>();
            partnerList     = new ArrayList<>();
            feedList        = new ArrayList<>();
            try {
                jsonObject = new JSONObject(JSON_STRING);

                JSONArray getEvent = jsonObject.getJSONArray(Config.TAG_JSON_EVENT);
                for (int i = 0; i < getEvent.length(); i++) {
                    int id              = getEvent.getJSONObject(i).getInt(Config.TAG_ID);
                    int eoId        = getEvent.getJSONObject(i).getInt(Config.TAG_EO_ID);
                    String eoName       = getEvent.getJSONObject(i).getString(Config.TAG_EO_NAME);
                    String title        = getEvent.getJSONObject(i).getString(Config.TAG_TITLE);
                    String day      = getEvent.getJSONObject(i).getString(Config.TAG_DAY);
                    String date         = getEvent.getJSONObject(i).getString(Config.TAG_DATE);
                    int price       = getEvent.getJSONObject(i).getInt(Config.TAG_PRICE);
                    event = new Event(id, eoId, eoName, title, day, date, price);
                    eventList.add(event);
                    if(Config.TODAY_DATE.equals(event.getDate())){
                        todayList.add(event);
                    } else {
                        upcomingList.add(event);
                    }

                }

                JSONArray getPartner = jsonObject.getJSONArray(Config.TAG_JSON_PARTNER);
                for (int i = 0; i < getPartner.length(); i++) {
                    int pId         = getPartner.getJSONObject(i).getInt(Config.TAG_ID);
                    String pName    = getPartner.getJSONObject(i).getString(Config.TAG_NAME);
                    String pEmail   = getPartner.getJSONObject(i).getString(Config.TAG_EMAIL);
                    String pPhone   = getPartner.getJSONObject(i).getString(Config.TAG_PHONE);
                    String pPhoto   = getPartner.getJSONObject(i).getString(Config.TAG_PHOTO_URL);
                    Partner partner = new Partner(pId, pName, pEmail, pPhone, pPhoto);
                    partnerList.add(partner);
                }

                JSONArray getArticle = jsonObject.getJSONArray(Config.TAG_JSON_ARTICLE);
                for (int i = 0; i < getArticle.length(); i++) {
                    int feedId              = getArticle.getJSONObject(i).getInt(Config.TAG_ID);
                    String feedAuthor       = getArticle.getJSONObject(i).getString(Config.TAG_FEED_AUTHOR);
                    String feedTitle        = getArticle.getJSONObject(i).getString(Config.TAG_FEED_TITLE);
                    String feedContent      = getArticle.getJSONObject(i).getString(Config.TAG_FEED_CONTENT);
                    String feedDate         = getArticle.getJSONObject(i).getString(Config.TAG_FEED_DATE);
                    String feedThumbnail    = getArticle.getJSONObject(i).getString(Config.TAG_FEED_THUMBNAIL);
                    Feed feed = new Feed(feedId, feedAuthor, feedTitle, feedContent, feedDate, feedThumbnail);
                    feedList.add(feed);
                }

            } catch (JSONException e) {
                e.printStackTrace();
            }
            return JSON_STRING;
        }

    }

    public static List<Feed> getFeedList(){ return feedList;}
    public static List<Event> getEventList() {return eventList;}
    public static List<Event> getTodayList() { return todayList;}
    public static List<Event> getUpcomingList() { return upcomingList;}
    public static List<Partner> getPartnerList() {return partnerList;}

}

DiscoverFragment.java

public class DiscoverFragment extends Fragment implements ViewPager.OnPageChangeListener, View.OnClickListener {

    protected View view;
    private LinearLayout pager_indicator;
    private int dotsCount;
    private ImageView[] dots;

    private List<Feed> feedList;
    private List<Event> eventList;
    private List<Partner> partnerList;

    public DiscoverFragment() {}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_discover, container, false);

        RecyclerView recyclerViewEvent      = (RecyclerView) view.findViewById(R.id.discover_event_recycler_view);
        RecyclerView recyclerViewPartner    = (RecyclerView) view.findViewById(R.id.discover_partner_recycler_view);

        ClickableViewPager intro_images = (ClickableViewPager) view.findViewById(R.id.pager_introduction);
        pager_indicator         = (LinearLayout) view.findViewById(R.id.viewPagerCountDots);

        eventList       = SplashScreenActivity.getEventList();
        partnerList     = SplashScreenActivity.getPartnerList();
        feedList        = SplashScreenActivity.getFeedList();

        EventAdapter eventAdapter = new EventAdapter(getContext(), eventList);
        DiscoverPartnerAdapter discoverPartnerAdapter = new DiscoverPartnerAdapter(getContext(), partnerList);
    DiscoverFeedAdapter mAdapter = new DiscoverFeedAdapter(getContext(), feedList);

        final LinearLayoutManager layoutManagerEvent = new LinearLayoutManager(getContext());
        final LinearLayoutManager layoutManagerPartner = new LinearLayoutManager(getContext());

        layoutManagerEvent.setOrientation(LinearLayoutManager.HORIZONTAL);
        layoutManagerPartner.setOrientation(LinearLayoutManager.HORIZONTAL);

        addBottomDots(0);
        intro_images.setAdapter(mAdapter);
        intro_images.setCurrentItem(0);
        intro_images.addOnPageChangeListener(this);
        intro_images.setOnItemClickListener(new ClickableViewPager.OnItemClickListener() {
            @Override
            public void onItemClick(int position) {
                Config.FEED_ID = position;
                startActivity(new Intent(getContext(), ArticleActivity.class));
            }
        });

        return view;
    }


    private void addBottomDots(int currentPage) {
        dots = new ImageView[feedList.size()]; //the problem
        pager_indicator.removeAllViews();
        for (int i = 0; i < dots.length; i++) {
            dots[i] = new ImageView(getContext());
            dots[i].setImageDrawable(getResources().getDrawable(R.drawable.nonselecteditem_dot));
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.WRAP_CONTENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT
            );
            params.setMargins(4, 0, 4, 0);
            pager_indicator.addView(dots[i], params);
        }
        if (dots.length > 0)
            dots[currentPage].setImageDrawable(getResources().getDrawable(R.drawable.selecteditem_dot));
    }


    @Override
    public void onClick(View v) {
        switch (v.getId()) {
        }
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
        addBottomDots(position);
        for (int i = 0; i < dotsCount; i++) {
            dots[i].setImageDrawable(getResources().getDrawable(R.drawable.nonselecteditem_dot));
        }
        dots[position].setImageDrawable(getResources().getDrawable(R.drawable.selecteditem_dot));
    }
}

LogCat

01-29 00:40:57.565 32535-32535/com.irmaelita.esodiaapp E/AndroidRuntime: FATAL EXCEPTION: main
                                                                         Process: com.irmaelita.esodiaapp, PID: 32535
                                                                         java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
                                                                             at com.irmaelita.esodiaapp.fragment.DiscoverFragment.addBottomDots(DiscoverFragment.java:181)
                                                                             at com.irmaelita.esodiaapp.fragment.DiscoverFragment.onCreateView(DiscoverFragment.java:158)

Answer 1

feedList is null. You create feedList instance when DownloadData task is executed. But you call feedList.size() in addBottomDots when fragment view should be created. So, most probably addBottomDots is called before DownloadData task is executed. You need to fix it.

Answer 2

The feedlist in your discover fragment is going empty while initializing. Please set a null check before doing so.It not about running from android studio.If I have understood it correctly you are trying to access a list from splasScreen activity after finishing it. ie in post execute you finish the current activity and the fragment is in main activity,so the list is going null.So if this is the case (and please correct me if not) then either download the data somewhere centrally or best way send it to main activity with intent and use it there. Also when running from android studio kill the app manually and run it again,while the phone is connected and see if it crashes in current scenario.

Answer 3

Send your data from doInBackground to MainActivity with sendBroadcast

Add broadcast method in DownloadData class

private void broadcast(SplashParcel parcel) {
    Intent i = new Intent("splash_parcel");
    i.putExtra("values", parcel);
    sendBroadcast(i);
}

@Override
protected String doInBackground(String... params) {
    // your code
    // ..
    try {
        // your code
        // ..


        // send splashParcel to MainActivity
        SplashParcel splashParcel = new SplashParcel(feedList, eventList, todayList, upcomingList, partnerList);
        broadcast (splashParcel);   

    } catch (JSONException e) {
        e.printStackTrace();
    }
    return JSON_STRING;
}

Add new class SplashParcel.java

 public class SplashParcel implements Parcelable { public static final Creator<SplashParcel> CREATOR = new Creator<SplashParcel>() { @Override public SplashParcel createFromParcel(Parcel in) { return new SplashParcel(in); } @Override public SplashParcel[] newArray(int size) { return new SplashParcel[size]; } }; private static List<Feed> _feedList; private static List<Event> _eventList; private static List<Event> _todayList; private static List<Event> _upcomingList; private static List<Partner> _partnerList; protected SplashParcel(Parcel in) { _feedList = new ArrayList<Feed>(); in.readList(_feedList, null); _eventList = new ArrayList<Event>(); in.readList(_eventList, null); _todayList = new ArrayList<Event>(); in.readList(_todayList, null); _upcomingList = new ArrayList<Event>(); in.readList(_upcomingList, null); _partnerList = new ArrayList<Partner>(); in.readList(_partnerList, null); } public SplashParcel(List<Feed> feedList, List<Event> eventList, List<Event> todayList, List<Event> upcomingList, List<Partner> partnerList) { _feedList = feedList; _eventList = eventList; _todayList = todayList; _upcomingList = upcomingList; _partnerList = partnerList; } public SplashParcel() { } public List<Feed> getFeedList() { return _feedList; } public void setFeedList(List<Feed> feedList) { _feedList = feedList; } public List<Event> getEventList() { return _eventList; } public void setEventList(List<Event> eventList) { _eventList = eventList; } public List<Event> getTodayList() { return _todayList; } public void setTodayList(List<Event> todayList) { _todayList = todayList; } public List<Event> getUpcomingList() { return _upcomingList; } public void setUpcomingList(List<Event> upcomingList) { _upcomingList = upcomingList; } public List<Partner> getPartnerList() { return _partnerList; } public void setPartnerList(List<Partner> partnerList) { _partnerList = partnerList; } @Override public int describeContents() { return 0; } @Override public void writeToParcel(Parcel parcel, int i) { parcel.writeList(_feedList); parcel.writeList(_eventList); parcel.writeList(_todayList); parcel.writeList(_upcomingList); parcel.writeList(_partnerList); } } 

MainActivity.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    SplashParcel splashParcel = getArguments().getParcelable("splash_parcel");  
    if(splashParcel != null) {  
        // your splashParcel ready in here
        List<Feed> feedList = splashParcel.getFeedList()
        List<Event> eventList = splashParcel.getEventList()
        List<Event> todayList = splashParcel.getTodayList();
        List<Event> upcommingList = splashParcel.getUpcomingList();
        List<Partner> partnerList = splashParcel.getPartnerList();
    }
}

In onCreateView of DiscoverFragment :

 @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { SplashParcel splashParcel = getArguments().getParcelable("splash_parcel"); if(splashParcel != null) { // your splashParcel ready in here List<Feed> feedList = splashParcel.getFeedList() List<Event> eventList = splashParcel.getEventList() List<Event> todayList = splashParcel.getTodayList(); List<Event> upcommingList = splashParcel.getUpcomingList(); List<Partner> partnerList = splashParcel.getPartnerList(); } }