我有一个使用AsyncTask的启动画面，它会从数据库下载一些数据并将数据存储在ArrayList中。这个ArrayList将用于RecyclerView的片段中的MainActivity.class。
问题是当我将应用程序从Android Studio运行到我的手机时，一切都运行良好。但是，当我销毁应用程序并从我的手机手动运行它时，它将显示空白的白色屏幕，然后它将崩溃。如果我在崩溃后再次运行，该应用程序将工作。因此，只有从Android Studio运行或崩溃后，此应用才会始终有效。
错误表明它是由空列表引起的。如果我没弄错的话，我认为活动被销毁后AsyncTask似乎无法正常工作。但我不知道如何解决它。请帮我解决这个问题。
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的
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)
答案 0 :(得分：0)
feedList为空。在执行feedList任务时创建DownloadData实例。但是，当您应创建片段视图时，请在feedList.size()中调用addBottomDots。因此，在addBottomDots任务执行之前，很可能会调用DownloadData。你需要解决它。
答案 1 :(得分：0)
初始化时，您的发现片段中的Feed列表将变空。请在设置之前设置一个空检查。它不是关于从android studio运行的。如果我已经正确理解了你，你试图在完成后从splasScreen活动中访问一个列表。即在post执行中你完成了当前的活动而片段在主要活动中，所以列表是null。所以如果是这种情况（如果不是，请纠正我）然后集中下载数据或最好的方式发送它有意图的主要活动并在那里使用它。此外，当从Android工作室运行时手动杀死应用程序并再次运行它，同时手机已连接，看看它是否在当前情况下崩溃。
答案 2 :(得分：-1)
使用 sendBroadcast
将数据从 doInBackground 发送到 MainActivity 在 DownloadData类中添加广播方法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;
}
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);
}
}
// member variable
private BroadcastReceiver _splashReceiver;
private Bundle _bundle = new Bundle();
@Override
protected void onResume() {
super.onResume();
splashReceiver();
}
// receive splashParcel from SplashScreenActivity
private void splashReceiver() {
if (_splashReceiver == null) {
_splashReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
SplashParcel splashParcel = intent.getParcelableExtra("values");
if (splashParcel != null) {
// save splashParcel into _budle
_bundle.putParcelable("splash_parcel", splashParcel);
}
}
};
registerReceiver(_splashReceiver, new IntentFilter("splash_parcel"));
}
}
//Send _bundle to DiscoverFragment
private void showDiscoverFragment(){
if(_bundle != null) {
// create instance of discoverFragment with passing _bundle as arguments
DiscoverFragment discoverFragment = new DiscoverFragment();
discoverFragment.setArguments(_bundle);
// replace activity_main.xml with discoverFragment
getSupportFragmentManager().beginTransaction().replace(R.id.main_container, discoverFragment).addBackStack(null).commit();
}
}
@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();
}
}