How to modify an external boolean value in a newly created listener in Java for Android

Question

I have an Android Fragment class that has a method to write something on an external firebase database after a button is clicked.

public class FR_Fragment extends Fragment implements View.OnClickListener {

    public void onClick(View view) {
        boolean writingSuccessfull = false;
        boolean writingNotSuccessfull = false;
        firebase_DB.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {

            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    writingSuccessfull = true;
                    writingNotSuccessfull = false;
                    Log.e("dbTAG",  "Data successfully written.");
                }
                else {
                    writingSuccessfull = false;
                    writingNotSuccessfull = true;
                    Log.e("dbTAG", task.getException().getMessage());
                }
            }
        });
    }
}

However, I somehow can't access the boolean variables writingSuccessfull and writingNotSuccessfull and that I define in the method onClick in the OnCompleteListener. With the shown code I get an error "Variable 'writingSuccessfull' is accessed from within inner class, needs to be final or effectively final"

When I let Android Studio fix this problem the code looks like this:

public class FR_Fragment extends Fragment implements View.OnClickListener {

    public void onClick(View view) {
        final boolean[] writingSuccessfull = { false };
        final boolean[] writingNotSuccessfull = { false };
        firebase_DB.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {

            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    writingSuccessfull[0] = true;
                    writingNotSuccessfull[0] = false
                    Log.e("dbTAG",  "Data successfully written.");
                }
                else {
                    writingSuccessfull[0] = false;
                    writingNotSuccessfull[0] = true
                    Log.e("dbTAG", task.getException().getMessage());
                }
            }
        });
    }
}

Now I can execute the code, but the values of the booleans do not change, even if the code inside the listener is executed. I also tried it without the "final" before the boolean variables. But this did not change anything. I can't modify the boolean variables inside this listener. But this is something that I need to do because I would like to know whether the data was written successfully into the database.

Any idea why I get this problem and how to solve it? I'll appreciate every comment.

Update: Here is the updated code with volatile and AtomicBooleas:

public class FR_Fragment extends Fragment implements View.OnClickListener {
    private volatile AtomicBoolean writingOrderToTheDatabaseWasSuccessful;
    private volatile AtomicBoolean writingOrderToTheDatabaseWasNotSuccessful;
...
public void onClick(View view) {

        int internalCounterAttempsWriteDataInTheFBDatabase =0;
        writingOrderToTheDatabaseWasSuccessful = new AtomicBoolean (false);
        writingOrderToTheDatabaseWasNotSuccessful = new AtomicBoolean (false);


        while(writingOrderToTheDatabaseWasSuccessful.get() == false && writingOrderToTheDatabaseWasNotSuccessful.get()==false) {
            internalCounterAttempsWriteDataInTheFBDatabase++;
            Log.e("LogTag", "internalCounterAttempsWriteDataInTheFBDatabase: " +internalCounterAttempsWriteDataInTheFBDatabase );
            Log.e("LogTag", "writingOrderToTheDatabaseWasSuccessful: " + writingOrderToTheDatabaseWasSuccessful.get());
            Log.e("LogTag", "writingOrderToTheDatabaseWasNotSuccessful: " + writingOrderToTheDatabaseWasNotSuccessful.get());


            DatabaseReference rootRef = FirebaseDatabase.getInstance("https://drink-server-db-default-rtdb.europe-west1.firebasedatabase.app").getReference();
            DatabaseReference ordersRef = rootRef.child("orders");
            String id =...;
            FirebaseDBItem_Order currentOrder = ...;

            ordersRef.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                 if (task.isSuccessful()) {
                      writingOrderToTheDatabaseWasSuccessful.set(true);
                      writingOrderToTheDatabaseWasNotSuccessful.set(false);
                      Log.e("dbTAG",  "Data successfully written.");
                      Log.e("LogTag", "Listener: writingOrderToTheDatabaseWasSuccessful: " + writingOrderToTheDatabaseWasSuccessful.get());
                      Log.e("LogTag", "Listener: writingOrderToTheDatabaseWasNotSuccessful: " + writingOrderToTheDatabaseWasNotSuccessful.get());

                 } else {

                    Log.e("dbTAG", task.getException().getMessage());
                 }
                    }//end method onComplete
                });//end addOnCompleteListener
            if (internalCounterAttempsWriteDataInTheFBDatabase >=10) {
                writingOrderToTheDatabaseWasNotSuccessful.set(true);
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }//end while loop
        Log.e("LogTag", "EndWhile: writingOrderToTheDatabaseWasSuccessful: " + writingOrderToTheDatabaseWasSuccessful.get());
        Log.e("LogTag", "EndWhile: writingOrderToTheDatabaseWasNotSuccessful: " + writingOrderToTheDatabaseWasNotSuccessful.get());


        //Show a toast about the order
        if (writingOrderToTheDatabaseWasSuccessful.get() ==true) {
            int duration = Toast.LENGTH_LONG;
            Toast toast = Toast.makeText(getContext(), getString(R.string.message_orderSubmittedSuccessfully), duration);
            toast.setGravity(Gravity.CENTER, 0, 0);
            toast.show();
        }

        if (writingOrderToTheDatabaseWasNotSuccessful.get() ==true) {
            int duration = Toast.LENGTH_LONG;
            Toast toast = Toast.makeText(getContext(), getString(R.string.message_orderSubmittedNotSuccessfully), duration);
            toast.setGravity(Gravity.CENTER, 0, 0);
            toast.show();
        }



        Navigation.findNavController(...);

    }//end method onClick

}//end class

The problem is the asnychronous call of the onComplete method. The code to change the booleans is not called immediately as it is in the onComplete method that is called asynchronously. This means in my example that the code in the onComplete method is just called after the 10 while-loop iterations and not during the loop as intended. The biggest question now is how to call any code in the onComplete method during the while loop.

Update: Here is the (relevant) output from logcat when running the code:

E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 1
    writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 2
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 3
    writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 4
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 5
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 6
    writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 7
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 8
    writingOrderToTheDatabaseWasSuccessful: false
E/LogTag: writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 9
    writingOrderToTheDatabaseWasSuccessful: false
    writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: internalCounterAttempsWriteDataInTheFBDatabase: 10
E/LogTag: writingOrderToTheDatabaseWasSuccessful: false
E/LogTag: writingOrderToTheDatabaseWasNotSuccessful: false
E/LogTag: EndWhile: writingOrderToTheDatabaseWasSuccessful: false
    EndWhile: writingOrderToTheDatabaseWasNotSuccessful: true
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
E/LogTag: Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
E/LogTag: Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
E/LogTag: Listener: writingOrderToTheDatabaseWasNotSuccessful: false
E/dbTAG: Data successfully written.
E/LogTag: Listener: writingOrderToTheDatabaseWasSuccessful: true
    Listener: writingOrderToTheDatabaseWasNotSuccessful: false

The result is that the item is saved 10 times in the firebase database. What I want is to try to store the item once in the firebase db. If this is successfull, the loop should stop and there should be a toast telling that it was successfull. If it was not successfull the loop should try it 10 times (with a delay of 1 second). If even after 10 attemps the item could not be stored in the firebase database, the loop should be stopped and there should be a toast message telling that the item could not be stored.

Answer 1

maybe you should not use boolean, you can use return method when the task succeeded and execute setValue() inside while(true) or for loop so when the task is successful the loop will stop working or when the loop reached to her limit. like this:

for (int i=0;i<5;i++) {
        firebase_DB.child("id").setValue("currentOrder").addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    Log.e("dbTAG", "Data successfully written.");
                    return;

                }
            }
        });
    }
    Toast.makeText(MainActivity.this, "ask for help",Toast.LENGTH_LONG);

Answer 2

Create a custom class that extends AndroidViewModel

        public class MyViewModel extends AndroidViewModel{

        private MutableLiveData<Boolean> writingSuccessful=new MutableLiveData<>();

            public MyViewModel(@NonNull Application application)
            {
                // you can do any other stuff here if you want
               }


            public void setBooleanWritingSuccessful(Boolean b)
            {
                writingSuccessful.setValue(b);
             }


            public LiveData<Boolean> getBooleanWritingSuccessful()
            {
               return writingSuccessful;
             }



        }

And then use this custom viewmodel class in your fragment for observing changes to the values

    public class FR_Fragment extends Fragment implements View.OnClickListener {
       

       private MyViewModel myViewModel;
       private boolean writingSuccessfull= false;



                @Override
                public void onCreate(Bundle savedInstanceState)
                {
                    // your stuffs

                    // initialize viewmodel

                    myViewModel=new ViewModelProvider(this,ViewModelProvider.AndroidViewModelFactory.getInstance(getActivity().getApplication())).get(MyViewModel.class);




                }





                @Override
                public void onCreateView(LayoutInflater inflater, ViewGroup container,
                                             Bundle savedInstanceState)
                {
                    
                        
                        // set your viewmodel for observing the changes in boolean values.

                        myViewModel.getBooleanWritingSuccessful().observe(getViewLifecycleOwner(),new Observer<Boolean>(){

                            @Override
                            public void onChanged(Boolean b)
                            {

                                // update your writingSuccessful variable here.
                                writingSuccessfull=b;

                            }
                        });



                }



    // In onClick update your viewmodel's mutablelivedata;

                    public void onClick(View view) {
                    ...

                    firebase_DB.child(id).setValue(currentOrder).addOnCompleteListener(new OnCompleteListener<Void>() {
                                     @Override
                                        public void onComplete(@NonNull Task<Void> task) {
                                         if (task.isSuccessful()) {


                                             //writingSuccessfull=true;
                                             //writingNotSuccessfull= false;

                                             //update the viewmodel's mutableLiveData 
                                             myViewModel.setBooleanWritingSuccessful(true);



                                             Log.e("dbTAG",  "Data successfully written.");

                                            } else {


                                             //writingSuccessfull=false;
                                             //writingNotSuccessfull= true;



                                             //update the viewmodel's mutableLiveData 
                                             myViewModel.setBooleanWritingSuccessful(false);


                                             Log.e("dbTAG", task.getException().getMessage());
                                            }
                                        }
                                });


                    }




                }

This is a simple snippet of the MVVM Architecture. Hope now it works. Thank you.