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Android app crashes when activity is initialised from fragment [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 9 months ago.
I am currently trying to create a calendar app in android studio. The app contains a calendar with different "Views" e.g. monthly view, weekly view, and daily view.
The app uses fragments as pages and each view is an activity.
This is the code for the fragment and buttons to initialise each view
public class CalendarFragment extends Fragment {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.fragment_calendar, container, false);
Button btn1 = (Button) v.findViewById(R.id.openCalendar);
btn1.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v)
{
Intent intent = new Intent(getActivity(),CalendarActivity.class);
startActivity(intent);
}
});
Button btn2 = (Button) v.findViewById(R.id.openWeek);
btn2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v)
{
Intent intent = new Intent(getActivity(), WeekViewActivity.class);
startActivity(intent);
}
});
return v;
}
The first button which displays the monthly view of the calendar called "CalendarActivity" in code works fine but when the second button is clicked which displays the weekly view of the calendar, causes the app to crash and gives the following error in the logcat
2022-05-13 14:44:59.642 15183-15183/com.example.finalyearproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.finalyearproject, PID: 15183
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.finalyearproject/com.example.finalyearproject.WeekViewActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.time.LocalDate.format(java.time.format.DateTimeFormatter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3685)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3842)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2252)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7842)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.time.LocalDate.format(java.time.format.DateTimeFormatter)' on a null object reference
at com.example.finalyearproject.CalendarUtils.monthYearFromDate(CalendarUtils.java:16)
at com.example.finalyearproject.WeekViewActivity.setWeekView(WeekViewActivity.java:40)
at com.example.finalyearproject.WeekViewActivity.onCreate(WeekViewActivity.java:29)
at android.app.Activity.performCreate(Activity.java:8054)
at android.app.Activity.performCreate(Activity.java:8034)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1341)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3666)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3842) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2252) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loopOnce(Looper.java:201) 
at android.os.Looper.loop(Looper.java:288) 
at android.app.ActivityThread.main(ActivityThread.java:7842) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) 
I am not sure what the problem is as I have been following a tutorial and the other features work. I have also included the code for each activity below.
Monthly View
public class CalendarActivity extends AppCompatActivity implements CalendarAdapter.OnItemListener {
private TextView monthYearText;
private RecyclerView calendarRecyclerView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_calendar);
initWidgets();
CalendarUtils.selectedDate = LocalDate.now();
setMonthView();
}
private void initWidgets()
{
calendarRecyclerView = findViewById(R.id.calendarRecyclerView);
monthYearText = findViewById(R.id.monthYearTV);
}
private void setMonthView()
{
monthYearText.setText(monthYearFromDate(CalendarUtils.selectedDate));
ArrayList<LocalDate> daysInMonth = daysInMonthArray(CalendarUtils.selectedDate);
CalendarAdapter calendarAdapter = new CalendarAdapter(daysInMonth, this);
RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getApplicationContext(), 7);
calendarRecyclerView.setLayoutManager(layoutManager);
calendarRecyclerView.setAdapter(calendarAdapter);
}
public void nextMonth(View view)
{
CalendarUtils.selectedDate = CalendarUtils.selectedDate.plusMonths(1);
setMonthView();
}
public void previousMonth(View view)
{
CalendarUtils.selectedDate = CalendarUtils.selectedDate.minusMonths(1);
setMonthView();
}
Weekly View
public class WeekViewActivity extends AppCompatActivity implements CalendarAdapter.OnItemListener {
private TextView monthYearText;
private RecyclerView calendarRecyclerView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_week_view);
initWidgets();
setWeekView();
}
private void initWidgets()
{
calendarRecyclerView = findViewById(R.id.calendarRecyclerView);
monthYearText = findViewById(R.id.monthYearTV);
}
private void setWeekView()
{
monthYearText.setText(monthYearFromDate(CalendarUtils.selectedDate));
ArrayList<LocalDate> days = daysInWeekArray(CalendarUtils.selectedDate);
CalendarAdapter calendarAdapter = new CalendarAdapter(days, this);
RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getApplicationContext(), 7);
calendarRecyclerView.setLayoutManager(layoutManager);
calendarRecyclerView.setAdapter(calendarAdapter);
}
public void previousWeek(View view)
{
CalendarUtils.selectedDate = CalendarUtils.selectedDate.minusWeeks(1);
setWeekView();
}
public void nextWeek(View view)
{
CalendarUtils.selectedDate = CalendarUtils.selectedDate.plusWeeks(1);
setWeekView();
}
Any suggestions would be greatly appreciated.

My suggestions:
Firstly you didn't initialized CalendarUtils.selectedDate
Cover code with breakpoints for. debugging or with Log.d() messages to find, which variable is null

Using Bundle to send data from activity to fragment

I am trying to use Bundle to send data from an activity to a fragment. The activity is receiving the input from a dialogbox when the user clicks on the actionbar add icon. The button also opens the dialogbox but it sends the data straight to the fragment (I'm trying to learn the difference between activity and fragment and to interact with the dialogfragment). None of the solutions on the internet have worked for me, and I was hoping someone can help
I have provided a visualization to aid in my explanation of the issue. So initially, I click the action add icon that opens the dialogbox (2nd pic), when I enter an input, it doesn't alter the data on the fragment. Only when I press the action add icon for a second time, does the first input get updated (3rd pic). Also you may notice that it says "Bundle{[Dialog Input = First Input]}" where First Input is the user input. How do I change this to just, First Input. I tried clearing the textview before setting the value, but that doesn't work. Now lastly when I press the button, it opens the dialogbox and when I enter in data, the data from the action add icon (handled in activity then data sent to fragment) overlaps with the data from the button (data sent straight to fragment). Any help would be appreciated. Thanks in advance.
MainActivity:
public class MainActivity extends AppCompatActivity implements
MyCustomDialog.OnInputSelected{
public String dialogInput;
FragmentManager fragmentManager;
#Override
public void sendInput(String input) {
dialogInput = input;
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentManager = getSupportFragmentManager();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
//Inflate the menu, this adds items to the action bar if it is present
getMenuInflater().inflate(R.menu.menu, menu);
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
//Handle action bar clicks here. The action bar will automatically handle clicks on the home/up button
//so long as you specify a parent activity in AndroidManifest.xml
switch(item.getItemId()){
case R.id.action_add:
MyCustomDialog dialog = new MyCustomDialog();
dialog.show(getSupportFragmentManager(), "MyCustomDialog");
//Trying Bundle to pass data, dialog input between activity and fragment
Bundle bundle = new Bundle();
bundle.putString("Dialog Input", dialogInput);
//Set Fragment class arguments
MainFragment fragment = new MainFragment();
fragment.setArguments(bundle); //set argument bundle to fragment
fragmentManager.beginTransaction().replace(R.id.MainFragment,fragment).commit(); //now replace Mainfragment
Toast.makeText(this, "Action_Add Clicked Successfully", Toast.LENGTH_SHORT).show();
}
return super.onOptionsItemSelected(item);
}
}
MainFragment:
public class MainFragment extends Fragment implements MyCustomDialog.OnInputSelected{
TextView InputDisplay;
Button OpenDialog;
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_main, container, false);
InputDisplay = view.findViewById(R.id.InputDisplay);
OpenDialog = view.findViewById(R.id.Open_Dialog);
//Getting Main Activity dialog information with Bundle, that was received from toolbar add
Bundle bundle = getArguments();
if(bundle != null){
String dialogInput = bundle.toString();
//Clearing since Fragment call and activity call overlap each other.
InputDisplay.setText("");
InputDisplay.clearComposingText();
InputDisplay.setText(dialogInput);
}
//String dialogInput = this.getArguments().getString("Dialog Input");
OpenDialog.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Log.d("MainFragment", "onClick: opening dialog");
MyCustomDialog customDialog = new MyCustomDialog();
customDialog.setTargetFragment(MainFragment.this, 1);
customDialog.show(getFragmentManager(), "MyCustomDialog");
}
});
return view;
}
#Override
public void sendInput(String input) {
InputDisplay.setText("");
InputDisplay.setText(input);
}
}
My Custom Dialog:
public class MyCustomDialog extends DialogFragment {
private EditText Input;
private TextView ActionOK, ActionCANCEL;
private OnInputSelected onInputSelected;
public interface OnInputSelected{
void sendInput(String input);
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
try{
Fragment onInputSelected_fragment = getTargetFragment();
Activity onInputSelected_activity = getActivity();
if(onInputSelected_fragment != null){
onInputSelected = (OnInputSelected) onInputSelected_fragment;
}else{
onInputSelected = (OnInputSelected) onInputSelected_activity;
}
//throw new RuntimeException("Custom Dialog onAttach Listener was NULL");
}catch(ClassCastException e){
Log.e("Custom Dialog", "onAttach: ClassCastException: " + e.getMessage());
}
}
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.dialog_my_custom, container, false);
Input = view.findViewById(R.id.Input);
ActionOK = view.findViewById(R.id.Action_OK);
ActionCANCEL = view.findViewById(R.id.Action_CANCEL);
ActionCANCEL.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
getDialog().dismiss();
}
});
ActionOK.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
onInputSelected.sendInput(Input.getText().toString());
getDialog().dismiss();
}
});
return view;
}
}

How do I change this to just, First Input.
your output is printed like this "Bundle{[Dialog Input = First Input]}" because you are directly doing bundle.toString(); instead of getting the value you have stored in the bundle.
change the above to this
String dialogInput = bundle.getString("Dialog Input")
InputDisplay.setText(dialogInput);
the data from the action add icon overlaps with the data from the button
Clear the existing text in the text view before setting the new value like this
String dialogInput = bundle.getString("Dialog Input")
InputDisplay.setText(");
InputDisplay.setText(dialogInput);
Also, I noticed that all the variable names that you have used are not following camel case I suggest you correct that as well.

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

How to update custom RecyclerView from FragmentDialog?

I have an Activity A with a fragment frag2. Inside the fragment I have a RecyclerView and Adapter to show a list of custom class objects. Adding objects to the adapter is handled programmatically. I have a button inside TwoFragment that opens a FragmentDialog. I'd like to add an object to my Adapter by confirming this dialog, but it seems that the adapter is null when called from the FragmentDialog.
The same adapter is not null, and works if I call it from the fragment OnClick.
Moreover the adapter is null only after screen rotation, it works fine before rotating.
To communicate between the two Fragments I implement a communicator class in activity A.
Activity A
public void respond(String type) {
frag2.addSupport(type);
}
frag2
public RecyclerView rv;
public ArrayList<support> supports;
public myAdapter adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
supports = new ArrayList<>();
adapter = new myAdapter(supports);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View layout = inflater.inflate( R.layout.fragment_two, container, false);
layout.setId(R.id.frag2);
if (savedInstanceState!=null)
{
supports = savedInstanceState.getParcelableArrayList("supports");
}
rv = (RecyclerView) layout.findViewById(R.id.rv);
adapter = new myAdapter(supports);
rv.setAdapter(myAdapter);
rv.setLayoutManager(new LinearLayoutManager(getActivity()));
rv.setItemAnimator(new DefaultItemAnimator());
#Override
public void onClick(View v) {
int id = v.getId();
switch (id){
case R.id.button1:
addSupport(type); // THIS WORKS ALWAYS, even after screen rotate
break;
case R.id.button2:
showDialog();
break;
}
}
public void showDialog(){
FragmentManager manager = getFragmentManager();
myDialog dialog = new myDialog();
dialog.show(manager, "dialog");
}
public void addSupport(String type){
adapter.addItem(new support(type)); // this line gives null pointer on adapter, but only if called after screen rotate and only if called from the dialog
}
dialog
communicator comm;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.dialog, null);
comm = (myCommunicator) getActivity();
create = (Button) view.findViewById(R.id.button_ok);
create.setOnClickListener(this);
return view;
}
#Override
public void onClick(View v) {
if(v.getId()==R.id.button_ok)
{
// some controls to set type
comm.respond(type)
dismiss();
}
else {
dismiss();
}
myAdapter
public class myAdapter extends RecyclerView.Adapter<myAdapter.VH> {
private LayoutInflater inflater;
private ArrayList<support> data = new ArrayList<>();
// settings for viewholder
public myAdapter (ArrayList<support> data)
{
this.data=data;
}
public void addItem(support dataObj) {
data.add(dataObj);
notifyItemInserted(data.size());
}
}
logcat
FATAL EXCEPTION: main
java.lang.NullPointerException: Attempt to invoke virtual method 'myAdapter.addItem(myObject)' on a null object reference
I hope there are no mistakes, I shortened the code for better understanding. Keep in mind that everything works if I never rotate the screen.
I'm a beginner with android and I'm stuck with this for several days now. Please, help.

To understand the problem, it's as you say:
.. everything works if I never rotate the screen
So firstly to understand what happens on rotation, this is a quote from the Android Developer website:
Caution: Your activity will be destroyed and recreated each time the user rotates the screen. When the screen changes orientation, the system destroys and recreates the foreground activity because the screen configuration has changed and your activity might need to load alternative resources (such as the layout).
Ok, now to understand the error:
FATAL EXCEPTION: main
java.lang.NullPointerException: Attempt to invoke virtual method 'myAdapter.addItem(myObject)' on a null object reference
Essentially, in your dialog class, you have created a strong dependency by declaring :
comm = (myCommunicator) getActivity();
because comm references objects which would have been destroyed on rotation, hence the NullPointerException.
To further understand runtime changes, such as orientation changes, I'd recommend going through Handling Runtime Changes.
Update
Thank you for your answer, what would you recommend instead of comm = (myCommunicator) getActivity(); ?
The solution comes in 3 parts:
Make sure the onCreate of Activity A has the following:
#Override
public void onCreate(Bundle savedInstanceState) {
......
// find the retained fragment on activity restarts
FragmentManager fm = getFragmentManager();
frag2 = (Frag2) fm.findFragmentByTag(“frag2”);
// create frag2 only for the first time
if (frag2 == null) {
// add the fragment
frag2 = new Frag2();
fm.beginTransaction().add(frag2 , “frag2”).commit();
}
......
}
Add setRetainInstance(true) to the onCreate of frag2.
Remove the implicit referencing i.e. comm = (myCommunicator) getActivity();, and implement something more loosely coupled for dialog.
dialog
public interface Communicator {
void respond(String type);
}
Communicator comm;
....
public void addCommunicator(Communicator communicator) {
comm = communicator;
}
public void removeCommunicator() {
comm = null;
}
#Override
public void onClick(View v) {
if((v.getId()==R.id.button_ok) && (comm!=null))
{
// some controls to set type
comm.respond(type);
}
// Regardless of what button is pressed, the dialog will dismiss
dismiss();
}
This allows you do the following in frag2 (or any other class for that matter):
frag2
<pre><code>
public class Frag2 extends Fragment implements dialog.Communicator {
........
public void showDialog() {
FragmentManager manager = getFragmentManager();
myDialog dialog = new myDialog();
dialog.addCommunicator(this);
dialog.show(manager, "dialog");
}
#Override
public void respond(String type){
adapter.addItem(new support(type));
}
}

Getting view of DialogFragment

I have created Dialog Fragment with custom layout and want to set text for some textboxes. But when trying to get view in my adapter image click I'm getting null pointer exception.
I would like to know is there any best way to implement it?
Thanks in advance.
Below is my code:
public class AlertDialogFragment extends DialogFragment
{
private View dialogView;
private static IDialogButtonsClicks buttonsClicks;
private AlertDialog.Builder alertDialog;
public static AlertDialogFragment newInstance(int title, int icon, int positive, int negative, int view, int message, IDialogButtonsClicks clicks)
{
AlertDialogFragment dialogFragment = new AlertDialogFragment();
Bundle args = new Bundle();
args.putInt("title", title);
args.putInt("icon", icon);
args.putInt("pos", positive);
args.putInt("neg", negative);
args.putInt("view", view);
args.putInt("message", message);
buttonsClicks = clicks;
dialogFragment.setArguments(args);
return dialogFragment;
}
#NonNull
#Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
alertDialog = new AlertDialog.Builder(getActivity());
int dView = getArguments().getInt("view");
int mess = getArguments().getInt("message");
if (dView != -1)
{
LayoutInflater layoutInflater = LayoutInflater.from(getActivity());
dialogView = layoutInflater.inflate(dView, null);
alertDialog.setView(dialogView);
}
if (mess != -1)
{
alertDialog.setMessage(mess);
}
alertDialog.setTitle(getArguments().getInt("title"));
alertDialog.setIcon(getArguments().getInt("icon"));
alertDialog.setPositiveButton(getArguments().getInt("pos"), new DialogInterface.OnClickListener()
{
#Override
public void onClick(DialogInterface dialog, int which)
{
buttonsClicks.OnPositiveButtonClick(dialogView);
}
});
alertDialog.setNegativeButton(getArguments().getInt("neg"), new DialogInterface.OnClickListener()
{
#Override
public void onClick(DialogInterface dialog, int which)
{
buttonsClicks.OnNegativeButtonClick();
}
});
return alertDialog.create();
}
public View getDialogView()
{
return dialogView;
}
#Nullable
#Override
public View getView()
{
return super.getView();
}
}
holder.imgCatEdit.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
AlertDialogFragment editCatDialog = AlertDialogFragment.newInstance(R.string.add_category_title, R.drawable.ic_edit, R.string.edit_cat_button_save, R.string.edit_cat_button_cancel, R.layout.edit_category, -1, new IDialogButtonsClicks()
{
#Override
public void OnPositiveButtonClick(View view)
{
}
#Override
public void OnNegativeButtonClick()
{
}
});
editCatDialog.show(((MyBusinessMainActivity)baseContext).getSupportFragmentManager(), "EditCatDialog");
View dialogView = editCatDialog.getView();//It seems here I'm getting null
EditText ed_edit_cat_name = (EditText)dialogView.findViewById(R.id.ed_edit_cat_name);
EditText ed_edit_cat_descr = (EditText)dialogView.findViewById(R.id.ed_edit_cat_descr);
ed_edit_cat_name.setText(cat_name);
ed_edit_cat_descr.setText(cat_descr);
}
});
11-23 12:40:49.708 19702-19702/am.nkr.mybusiness E/AndroidRuntime: FATAL EXCEPTION: main
Process: am.nkr.mybusiness, PID: 19702
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at am.nkr.mybusiness.CategoriesAdapter$2.onClick(CategoriesAdapter.java:165)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

It is because when you do editCatDialog.getView(); the view have not been yet initializied (onCreateDialog() was not called).
The best way would be to add listeners in dialog in onViewCreated method. Then passing those events to your main fragment (e.g. via buttonClicks variable).
If you want to make it in a quick and hacky way you could write getSupportFragmentManager().executePendingTransaction() after show method

Yeah, you got that error because when you call ed_edit_cat_name.setText(cat_name);, your DialogFragment callback onCreateView is not finished! To overcome this problem, I think you can declare some variables to hold your cat_name and cat_des in your DialogFragment as below:
public class AlertDialogFragment extends DialogFragment
{
private String catName;// getter - setter
private String catDes;//getter-setter
// TODO: find your view and set cat name, description in onCreateView callback.
}
Then, you can set your cat name, cat des when you create new instance of DialogFragment.