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По какой-то причине в моем приложении, когда я пытаюсь вызвать openFileOutput (), он генерирует исключение NullPointerException, и я не уверен, что его вызывает. Я убедился, что все параметры метода не являются нулевыми, но по какой-то причине мое приложение по-прежнему бросает исключение NullPointerException. Какие-либо предложения?Попытка вызвать виртуальный метод 'java.io.FileOutputStream android.content.Context.openFileOutput (java.lang.String, int)' на ссылке нулевого объекта
Мой MainActivity класс
public class MainActivity extends AppCompatActivity {
private static final String TAG_NEWS_FRAGMENT = "news_fragment";
private static final String TAG_SPORTS_FRAGMENT = "sports_fragment";
Context context = MainActivity.this;
private final String[] CATEGORY_NAMES = {"news", "sports"};
private Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager viewPager;
private ProgressBar mProgressBar;
private CoordinatorLayout coordinatorLayout;
private PUNewsFragment mPUNewsFragement;
private PUSportsFragment mPUSportsFragement;
private List<NewspaperMetaObject> newsItems;
private List<List<NewspaperMetaObject>> categories;
private boolean doesFileExist;
private boolean isWebsiteOnline;
private FragmentManager fm;
private ProgressBar pb;
private boolean doRefresh;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
doRefresh = false;
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
viewPager = (ViewPager) findViewById(R.id.viewpager);
tabLayout = (TabLayout) findViewById(R.id.tabs);
Toast.makeText(this, "Loading...", Toast.LENGTH_SHORT).show();
pb = (ProgressBar) findViewById(R.id.progressBar);
try {
isWebsiteOnline = new checkWebsiteStatus().execute().get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
doesFileExist = new File(context.getFilesDir() + "/news").exists();
new RetrieveNewspaperMeta().execute(CATEGORY_NAMES);
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new PUNewsFragment(), "News");
adapter.addFragment(new PUSportsFragment(), "Sports");
viewPager.setAdapter(adapter);
}
public void refresh(String[] str) {
doRefresh = true;
new RetrieveNewspaperMeta().execute(str);
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
@Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
@Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
@Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
private class RetrieveNewspaperMeta extends AsyncTask<String, Integer, Wrapper> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected Wrapper doInBackground(String... params) {
Document doc = null;
categories = new ArrayList<>();
if (!doesFileExist && doRefresh) {
for (int i = 0; i < params.length; i++) {
newsItems = new ArrayList<>();
try {
Log.i("DEBUG", params[i]);
URL url = new URL("http://www.dailyprincetonian.com/category/" + params[i] + "/");
doc = Jsoup.connect(url.toString()).get();
Elements content = doc.select("article.tease-post");
System.out.println();
System.out.println(content);
int count = 0;
NewspaperMetaObject parser;
while (!content.eq(count).isEmpty()) {
parser = new NewspaperMetaObject(content.eq(count));
newsItems.add(parser);
count++;
}
categories.add(newsItems);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
for (NewspaperMetaObject o : newsItems) {
try {
Elements text = Jsoup.connect(o.getDoc().select("h3.h2 a").attr("href")).get().select("section.article-content").select("div.article-bd").select("p");
o.setArticleText(text.toString());
} catch (IOException e) {
e.printStackTrace();
}
}
}
return new Wrapper(categories, params);
} else {
for (int i = 0; i < params.length; i++) {
newsItems = new ArrayList<>();
try {
FileInputStream fis = openFileInput(params[i]);
ObjectInputStream is = new ObjectInputStream(fis);
newsItems = (List<NewspaperMetaObject>) is.readObject();
is.close();
fis.close();
categories.add(newsItems);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (StreamCorruptedException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
return new Wrapper(categories, params);
}
}
@Override
protected void onProgressUpdate(Integer... values) {
}
@Override
protected void onPostExecute(final Wrapper wrapper) {
super.onPostExecute(wrapper);
android.os.Handler mHandler = new android.os.Handler();
mHandler.postDelayed(new Runnable() {
@Override
public void run() {
if (!doRefresh) {
PUNewsFragment.newsItems = categories.get(0);
PUSportsFragment.newsItems = categories.get(1);
setupViewPager(viewPager);
tabLayout.setupWithViewPager(viewPager);
fm = getSupportFragmentManager();
mPUNewsFragement = (PUNewsFragment) fm.findFragmentByTag(TAG_NEWS_FRAGMENT);
mPUSportsFragement = (PUSportsFragment) fm.findFragmentByTag(TAG_SPORTS_FRAGMENT);
if (mPUNewsFragement == null && mPUSportsFragement == null) {
mPUNewsFragement = new PUNewsFragment();
mPUSportsFragement = new PUSportsFragment();
fm.beginTransaction().add(mPUNewsFragement, TAG_NEWS_FRAGMENT).commit();
fm.beginTransaction().add(mPUSportsFragement, TAG_SPORTS_FRAGMENT).commit();
}
} else {
for (int i = 0; i < wrapper.params.length; i++) {
switch (wrapper.params[i]) {
case "news":
PUNewsFragment.newsItems = categories.get(0);
PUNewsFragment.adapter.notifyDataSetChanged();
break;
case "sports":
PUSportsFragment.newsItems = categories.get(1);
PUSportsFragment.adapter.notifyDataSetChanged();
break;
}
}
}
if (pb != null) {
pb.setVisibility(View.GONE);
}
Log.i("DEBUG", "DONE!");
if (doRefresh) {
context = MainActivity.this;
for (int i = 0; i < wrapper.params.length; i++) {
try {
FileOutputStream fos = context.openFileOutput(wrapper.params[i], 0);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(newsItems);
os.close();
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
doRefresh = false;
}
}, 1000);
}
}
private class checkWebsiteStatus extends AsyncTask<Void, Void, Boolean> {
@Override
protected Boolean doInBackground(Void... params) {
try {
URL url = new URL("http://www.dailyprincetonian.com/");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.connect();
urlConnection.disconnect();
return true;
} catch (IOException e) {
}
return false;
}
}
private class Wrapper {
List<List<NewspaperMetaObject>> categories;
String[] params;
public Wrapper(List<List<NewspaperMetaObject>> categories, String[] params){
this.categories = categories;
this.params = params;
}
}
}
Отрывок, где Исключение выбрасывают
if (doRefresh) {
context = MainActivity.this;
for (int i = 0; i < wrapper.params.length; i++) {
try {
FileOutputStream fos = context.openFileOutput(wrapper.params[i], 0);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(newsItems);
//os.flush();
os.close();
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}