Data being lost after addValueEventListener Firebase Android

Question

In the addValueEventListener I am getting data for firebase database correctly. I copy that data to a variable called newDay. However, once I am out of the addValueEventListener, the data is gone. How do I make sure the data stays?

        mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();
        String current_uid = mCurrentUser.getUid();
        mUserDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(current_uid).child("week").child(day);
        newDay = new ArrayList<Integer>();
        mUserDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                newDay.addAll((ArrayList<Integer>)dataSnapshot.getValue());
                Log.d("newday", "onDataChange:"+newDay.toString());

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
        Log.d("after","value " +newDay.toString());

These are the log results:

03-04 00:01:28.475 7961-7961/com.example.fake9.tendee D/newday: onDataChange:[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

In after, newDay is strangely empty.

03-04 00:04:54.665 9906-9906/com.example.fake9.tendee D/after: value []

Entire code provided if details are not enough. Many parts are irrelevant it seems:

public class ScheduleActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

    private Toolbar mToolbar;
    private Spinner chooseDay;
    private TimePicker startTime;
    private TimePicker endTime;
    private Button busyBtn;
    private Button freeBtn;
    String day;
    Map<String,ArrayList<Integer>> changeweek;
    ArrayList<Integer> test;
    ArrayList<Integer> newDay;

    private DatabaseReference mUserDatabase;
    private FirebaseUser mCurrentUser;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_schedule);

        mToolbar = (Toolbar)findViewById(R.id.schedule_toolbar);
        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setTitle("Schedule");

        chooseDay = (Spinner)findViewById(R.id.chooseDay_spinner);
        chooseDay.setOnItemSelectedListener(this);
        List<String> week = new ArrayList<String>();
        week.add("Monday");
        week.add("Tuesday");
        week.add("Wednesday");
        week.add("Thursday");
        week.add("Friday");
        ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item,week);
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        chooseDay.setAdapter(dataAdapter);

        startTime = (TimePicker)findViewById(R.id.start_timePicker);
        endTime = (TimePicker)findViewById(R.id.end_timePicker);
        freeBtn = (Button)findViewById(R.id.free_btn);
        freeBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int startHour = startTime.getCurrentHour();
                int startMin = startTime.getCurrentMinute();
                int endHour = endTime.getCurrentHour();
                int endMin = endTime.getCurrentMinute();
                int startIndex = 0;
                int endIndex = 0;
                int intervals = 0;
                //Log.d("hour", "onClick: "+startHour);
                //Log.d("minute", "onClick: "+startMin);
                if (startHour < 9 || startHour > 17 || endHour < 9 || endHour > 17) {
                    Toast.makeText(ScheduleActivity.this, "invalid time", Toast.LENGTH_SHORT).show();
                    return;
                }
                if (startHour > endHour) {
                    Toast.makeText(ScheduleActivity.this, "impossible time", Toast.LENGTH_SHORT).show();
                    return;
                }
                startIndex = (startHour - 9) * 2;
                if (startMin >= 30) {
                    startIndex = startIndex + 1;
                }
                //Log.d("startIndex", "onClick: "+startIndex);
                endIndex = (endHour - 9) * 2;
                if (endMin >= 30) {
                    endIndex = endIndex + 1;
                }
                final int finalstart = startIndex;
                final int finalend = endIndex;
                //Log.d("endIndex", "onClick: "+endIndex);
                mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();
                String current_uid = mCurrentUser.getUid();
                mUserDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(current_uid).child("week").child(day);
                newDay = new ArrayList<Integer>();
                mUserDatabase.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        newDay.addAll((ArrayList<Integer>)dataSnapshot.getValue());
                        Log.d("newday", "onDataChange:"+newDay.toString());

                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
                Log.d("after","value " +newDay.toString());
                intervals = endIndex - startIndex;
                for (int i = startIndex; i < endIndex; i++) {
                    Log.d("indexes", "onClick: "+i);
                }
            }
        });
    }

Possible duplicate of [How to return dataSnapshot value as a result of a method?](https://stackoverflow.com/questions/47847694/how-to-return-datasnapshot-value-as-a-result-of-a-method) — Alex Mamo, Mar 04 '18 at 10:18

Nouman Ch · Accepted Answer · 2018-03-04T05:32:24.457

1

The line

Log.d("after","valu" + newDay.toString());

is calling before firebase gets result from database. All you need to do is create a method

public void printResult(){
  Log.d("after","valu" + newDay.toString());
}

Now call this method as

newDay = new ArrayList<Integer>();
        mUserDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {


newDay.addAll((ArrayList<Integer>)dataSnapshot.getValue());
                Log.d("newday", "onDataChange:"+newDay.toString());
                printResult();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Reason

Firebase has it's own async mechanism like volley library onDataChange function will be call when firebase gets some result from internet and execute the below code as normally in your case below code is your Log.d("after","value"+newDay.toString()); line.

Hope this will help you.

edited Mar 04 '18 at 05:32

answered Mar 04 '18 at 05:29

Nouman Ch

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Ah I see. So just to be clear, the data is in newDay after all? It just takes a while for firebase to put it in? – Avinash Prabhakar Mar 04 '18 at 05:31
Because I am going to need to use newDay for other things and it would be problematic if it is still empty. – Avinash Prabhakar Mar 04 '18 at 05:31
yes definetly it takes a while to put data into it. – Nouman Ch Mar 04 '18 at 05:33
no it won't be problematic if you put all your login in printResult method or call any method after loading data in onDataChange method. – Nouman Ch Mar 04 '18 at 05:33
I have another huge problem actually. Once I modify newDay I will need to push it back into firebase database. If I do that, I will get infinite loop since data is always changing. So onDataChange will keep executing. – Avinash Prabhakar Mar 04 '18 at 05:35
I need to be able to use newDay variable outside addValueEventListener. But outside it is empty. – Avinash Prabhakar Mar 04 '18 at 05:36
simple solution for this is to avoid from infinite loop put simple condition there that if you have data that needs to be updated then update id else just quit the onDataChange method. – Nouman Ch Mar 04 '18 at 05:37
I am not exactly sure how to do that. Any data update to the database would trigger onDatachange again. I just setValue to update it. Once setValue executes it will call onDataChange again. – Avinash Prabhakar Mar 04 '18 at 05:42
Is there way to use newDay outside of onDataChange and addValueEventListener? If I can do that, then I can update the database outside of onDatachange. – Avinash Prabhakar Mar 04 '18 at 05:43
can I make the app wait or sleep until firebase puts the data in newDay? – Avinash Prabhakar Mar 04 '18 at 05:45
yes dear u don't need to do anything extra just replace all the code which is below firebase code and put this all into a method and call this method from onDataChange method. – Nouman Ch Mar 04 '18 at 05:49
this will fulfil your purpose of waiting for data to come from internet and making newDay array filled. – Nouman Ch Mar 04 '18 at 05:51
Okay I will try it out. – Avinash Prabhakar Mar 04 '18 at 05:51
mark question as correct if you feel it is help ful and upvote it.thanks – Nouman Ch Mar 04 '18 at 05:54
1

Thank you for your continued assistance. I will mark it in a few minutes, – Avinash Prabhakar Mar 04 '18 at 05:56
Hey it seems to functioning now. But I am getting another problem. I'll update the question. – Avinash Prabhakar Mar 04 '18 at 06:17
Actually its been fixed. Thank you so much for you help. You have saved me hours of frustration. – Avinash Prabhakar Mar 04 '18 at 06:24

Data being lost after addValueEventListener Firebase Android

1 Answers1