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How to replace a fragment from onOptionsItemSelected? [duplicate]

This question already has answers here:
findViewById in Fragment
(37 answers)
Closed 5 years ago.
I've got an AppCompatActivity which is the main View of the app.
There I've got an OptionsMenu with a button to display a drawer menu and another button to filter the results (Because each MenuItem in the drawer are different Listfragments).
What I need to accomplish is, when clicking the filter button on the OptionsMenu, open a fragment with all the filtering criteria.
So this is the code managing the explained above:
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_menu:
if (drawer.isDrawerOpen(GravityCompat.START)) {
hideDrawer();
} else {
showDrawer();
}
return true;
case R.id.action_filter:
fragmentManager = getFragmentManager();
fragment = new FilterFragment();
args.putInt("idList", idList);
fragment.setArguments(args);
fragmentManager.beginTransaction().replace(R.id.drawer_layout, fragment).commit();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
Doing that the Fragment shows up and then I get a NPE:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TableRow.setVisibility(int)' on a null object reference
Fragment onCreateViewMethod
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, Bundle savedInstanceState) {
setHasOptionsMenu(true);
getActivity().invalidateOptionsMenu();
skbrDays = getActivity().findViewById(R.id.seekBar);
daysLostRow = getActivity().findViewById(R.id.daysLostRow);
genderRow = getActivity().findViewById(R.id.genderRow);
locationRow = getActivity().findViewById(R.id.locationRow);
rgupGender = getActivity().findViewById(R.id.rgupGender);
rgupType = getActivity().findViewById(R.id.rgupType);
btnBreed = getActivity().findViewById(R.id.btnBreed);
recyclerView = getActivity().findViewById(R.id.recyclerView);
daysLostRow.setVisibility(View.VISIBLE);
return inflater.inflate(R.layout.activity_filter, container, false);
}
Ok, so I'm getting the NPE because getActivity() is returning null. And now I have to guess, not really knowing the reason, that is beacuse I'm not replacing the fragment on onCreate method from the activity?
If that is the reason how can I achieve the same result calling the fragment from onCreate?

Replace your code in onCreateView to below code.
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_filter, container, false);
setHasOptionsMenu(true);
getActivity().invalidateOptionsMenu();
skbrDays = rootView.findViewById(R.id.seekBar);
daysLostRow = rootView.findViewById(R.id.daysLostRow);
genderRow = rootView.findViewById(R.id.genderRow);
locationRow = rootView.findViewById(R.id.locationRow);
rgupGender = rootView.findViewById(R.id.rgupGender);
rgupType = rootView.findViewById(R.id.rgupType);
btnBreed = rootView.findViewById(R.id.btnBreed);
recyclerView = rootView.findViewById(R.id.recyclerView);
daysLostRow.setVisibility(View.VISIBLE);
return rootView;
}

ListView of a Fragment (of a ViewPager inside a Fragment) that implements LoaderCallbacks<Cursor> is empty when I return back to it

The ListView inside of a Fragment that contains a ViewPager is empty when I return back to it. This ViewPager is inside of a Fragment because I'm using a Navigation Drawer Layout. I'll try to explain it in more details now:
I am using a Navigation Drawer layout and, consequently, using Fragments. In the main activity, in onCreate, I set the current Fragment with these lines of code:
#Override
protected void onCreate(Bundle savedInstanceState) {
/* More code */
currentFragment = new MainFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
}
The MainFragment class contains a ViewPager that is initialized with these lines of code in the onCreateView():
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
/* More code */
ViewPager viewPager = (ViewPager) rootView.findViewById(R.id.main_view_pager);
viewPager.setAdapter(new SimpleFragmentPagerAdapter(getActivity(), getActivity().getSupportFragmentManager()));
/* Code for Tablayout */
return rootView;
}
One of the Fragments of the SimpleFragmentPagerAdapter class is this one that implements LoaderManager.LoaderCallbacks
public class ExpensesFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor> {
private ExpenseCursorAdapter mExpenseCursorAdapter;
private static final int EXPENSE_LOADER = 1;
public ExpensesFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_expenses, container, false);
ListView expensesListView = (ListView) rootView.findViewById(R.id.expenses_list_view);
mExpenseCursorAdapter = new ExpenseCursorAdapter(getContext(), null);
expensesListView.setAdapter(mExpenseCursorAdapter);
getLoaderManager().initLoader(EXPENSE_LOADER, null, this);
return rootView;
}
#Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
return new CursorLoader(/* arguments */);
}
#Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
mExpenseCursorAdapter.swapCursor(data);
}
#Override
public void onLoaderReset(Loader<Cursor> loader) {
mExpenseCursorAdapter.swapCursor(null);
}
}
On the first run, everything works fine. However, if I click on the navigation drawer menu, which I'm implementing this way, the ListView becomes empty:
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
if (id == R.id.nav_main) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().remove(currentFragment).commit();
currentFragment = new MainFragment();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
} else if (id == R.id.nav_blank) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().remove(currentFragment).commit();
currentFragment = new BlankFragment();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
}
drawer.closeDrawer(GravityCompat.START);
return true;
}
The problem also exists when I rotate the device. There is a difference though. When I use the Navigation Drawer menu, none of the methods of the LoaderManager.LoaderCallbacks are called, but when I rotate the device, onLoadFinished is called.
Anyway, the problem persists. Any ideias how to solve it?
Thanks in advance.

I have found the solution!
Basically, I made two mistakes.
The first one is about the rotation of the device.
When the device is rotated, the Activity is destroyed and onCreate is called again. In this case, I should't call new MainFragment(). So, I check if the savedInstanceState is null before I call it, like this:
if (savedInstanceState == null) {
currentFragment = new MainFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().
replace(R.id.layout_for_fragments, currentFragment).commit();
}
The second one is about a fragment within a fragment. In this case, I can't simply call getSupportFragmentManager(). I should call getChildFragmentManager() instead and that's it!

error: cannot find symbol method getSupportActionBar(),findViewById(int),getApplicationContext()

So I have this code inside my ScheduleFragment in which my objective was to view a simple calendar viewer. But unfortunately, it gets an error mentioned in the title. Even if I change "public class ScheduleFragment extends Fragment" to "public class ScheduleFragment extends AppCompatActivity", it gives an error to #Override.
#TargetApi(Build.VERSION_CODES.N)
public class ScheduleFragment extends Fragment {
CompactCalendarView compactCalendar;
private SimpleDateFormat dateFormatMonth = new SimpleDateFormat("MMM - yyyy", Locale.getDefault());
public ScheduleFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_schedule, container, false);
final ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(false);
actionBar.setTitle(null);
compactCalendar = (CompactCalendarView) findViewById(R.id.compactcalendar_view);
compactCalendar.setUseThreeLetterAbbreviation(true);
Event ev1 = new Event(Color.RED, 1477040400000L, "Teachers' Professional Day");
compactCalendar.addEvent(ev1);
compactCalendar.setListener(new CompactCalendarView.CompactCalendarViewListener() {
#Override
public void onDayClick(Date dateClicked) {
Context context = getApplicationContext();
if (dateClicked.toString().compareTo("Fri Oct 21 00:00:00 AST 2016") == 0) {
Toast.makeText(context, "Teachers' Professional Day", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(context, "No Events Planned for that day", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onMonthScroll(Date firstDayOfNewMonth) {
actionBar.setTitle(dateFormatMonth.format(firstDayOfNewMonth));
}
});
}
}

In fragments, you can not directly call findViewById() and have to use the view that you just inflated and call findViewById() on it.
So your onCreateView code will be,
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.fragment_schedule, container, false);
compactCalendar = (CompactCalendarView) v.findViewById(R.id.compactcalendar_view);
//Make sure that the view inflated above has these view elements which you are trying to initialize
.
.
.
}
Similarly for getApplicationContext(), you first need to call getContext() and then call getApplicationContext() on it
So it becomes,
Context c = getContext().getApplicationContext();
Same goes for getSupportActionBar();

In my opinion, you should inflate the view and use view.findViewByID(R.id.id),
then call return at the end of the method .

NullPointerException using fragment transactions [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
I'm starting with android and just getting crazy with the implements of multiple fragments.
I have two fragments in my MainActivity: QuestionDetail and QuestionListFragment.
When I use a fragment transactions to replace the QuestionDetail fragment when someone click in one of the QuestionListFragment options I get a NullPointerException error.
I have been trying to fix this issue for hours. Any help is greatly appreciated.
QuestionDetail
public class QuestionListFragment extends Fragment{
private RecyclerView recView;
public static QuestionAdapter adapter;
private QuestionListener listener;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_question_list, container, false);
recView = (RecyclerView) v.findViewById(R.id.recView);
return v;
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recView.setLayoutManager(layoutManager);
adapter = new QuestionAdapter(QuestionCatalog.getQuestionCatalog().getQuestionList().getList());
adapter.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
if (listener!=null) {
listener.onQuestionListener(adapter.getItem(recView.getChildAdapterPosition(v)));
}
}
});
recView.setAdapter(adapter);
}
public interface QuestionListener {
void onQuestionListener(Question q);
}
public void setQuestionListener(QuestionListener listener) {
this.listener=listener;
}
QuestionDetail
public class QuestionDetail extends Fragment {
// We use an ID to know which Question we're using
private long questionId;
public QuestionDetail() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_question_detail, container, false);
}
#Override
public void onStart() {
super.onStart();
//Fragments don’t include findViewById(). To get a reference to a view, we use getView()
View view = getView();
if (view != null) {
TextView title = (TextView) view.findViewById(R.id.textQuestion);
Question question = QuestionCatalog.getQuestionCatalog().getQuestionList().getList().get((int) questionId);
title.setText(question.getName());
TextView kind = (TextView) view.findViewById(R.id.textKind);
kind.setText(question.getKind());
}
}
public void showDetails(String texto) {
TextView txtName = (TextView)getView().findViewById(R.id.textQuestion);
TextView txtKind = (TextView)getView().findViewById(R.id.textKind);
txtName.setText(texto);
txtKind.setText(texto);
}
}
MainActivity
public class MainActivity extends AppCompatActivity implements QuestionListFragment.QuestionListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
QuestionListFragment frg =(QuestionListFragment)getFragmentManager().findFragmentById(R.id.listFragment);
frg.setQuestionListener(this);
}
#Override
public void onQuestionListener(Question q) {
Toast.makeText(this, "num: " + q.getName(),
Toast.LENGTH_LONG).show();
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
QuestionDetail f1 = new QuestionDetail();
f1.showDetails(q.getName());
t.replace(R.id.detailFragment,f1);
t.addToBackStack(null);
t.commit();
}
stacktrace
08-04 09:54:11.914 22277-22277/com.hfad.predictandwin E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at com.hfad.predictandwin.Fragments.QuestionDetail.showDetails(QuestionDetail.java:50)
at com.hfad.predictandwin.MainActivity.onQuestionListener(MainActivity.java:34)
at com.hfad.predictandwin.Fragments.QuestionListFragment$1.onClick(QuestionListFragment.java:55)
at com.hfad.predictandwin.QuestionAdapter.onClick(QuestionAdapter.java:61)
at android.view.View.performClick(View.java:4475)
at android.view.View$PerformClick.run(View.java:18786)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:176)
at android.app.ActivityThread.main(ActivityThread.java:5419)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
at dalvik.system.NativeStart.main(Native Method)

First, don't use getView() in onStart() - You shouldn't have a view to get at that point. Second, you shouldn't be calling methods directly on the Fragment instances from elsewhere, in your case f1.showDetails(q.getName());. There, again, the Fragment has no View. Please see Best practice for instantiating a new Android Fragment for how to pass arguments into Fragment before you load it into the FragmentManager.
Next point - you should initialize your views using findViewById inside of onCreateView just like you did for the other Fragment class. For example,
private TextView txtName, txtKind;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_question_detail, container, false);
txtName = (TextView) rootView.findViewById(R.id.textQuestion);
txtKind = (TextView) rootView.findViewById(R.id.textKind);
// TODO: Read the link how to use these
Bundle arguments = getArguments();
Question question = QuestionCatalog.getQuestionCatalog()
.getQuestionList().getList().get((int) questionId);
showQuestion(question);
return view;
}
private void showQuestion(Question q) {
txtName.setText(q.getName());
txtKind.setText(q.getKind());
}

in QuestionListFragment:
We set click listener for recView, not adapter. You should replace adapter.setOnClickListener with
recView.addOnItemTouchListener(new RecyclerTouchListener(getApplicationContext(), recView, new ClickListener() {
#Override
public void onClick(View view, int position) {
// do something with position.
}
#Override
public void onLongClick(View view, int position) {
}
}));
in QuestionDetail:
questionId wasn't initialized but you have use it in this line:
Question question = QuestionCatalog.getQuestionCatalog().getQuestionList().getList().get((int) questionId);

Based on stacktrace and your code (not sure which one is line #50 in your QuestionDetail) ether txtName or txtKind evaluates to null (maybe both), so for whatever reason getView().findViewById(R.id.textQuestion) returns null. Probably because getView() in that call doesn't get you a parent view of the TextView in question

Android Studio - Fragment button action

I tried to make an application that shows a fragment at start then you can change that fragment to an other one with a button in the first fragment. But when I put the button action in the fragments java, it won't start and I get the nullpointerexception error. Could you tell me why?
public class Fragment_main extends Fragment {
FragmentManager fm = getFragmentManager();
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
Button button_inditas = (Button) getView().findViewById(R.id.button_inditas);
button_inditas.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
fm.beginTransaction().replace(R.id.content_frame, new Fragment_1()).commit();
}
});
return inflater.inflate(R.layout.fragment_main,container,false);
}
}

But when I put the button action in the fragments java, it won't start and I get the nullpointerexception error. Could you tell me why?
Well I see some errors on your code...
First of all you can't call getView() if you haven't inflated one, it means that you MUST inflate a view as i'll put on my answer and then you can avoid the getView() and use that view itself.
And instead of returning the inflater you have to return your View
This is how your Fragment should look like:
public class Fragment_main extends Fragment {
public Fragment_main() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main,container,false);
Button button_inditas = (Button)rootView.findViewById(R.id.button_inditas);
button_inditas.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
FragmentManager fragmentManager = getFragmentManager ();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction ();
fragmentTransaction.add (R.id.content_frame, new Fragment_1());
fragmentTransaction.commit ();
});
return rootView;
}
}

You have to inflate the view first and use the view returned by that instead of getView ().
View view = inflater.inflate (...);
and then
... = (Button) view.findView(...);
This happens because the view that is returned by getView () hasn't been created yet, so getView() returns null.