add value to json object in for loop java

Question

I have defined new json object and array.

 private JSONArray array = new JSONArray();
 private JSONObject obj = new JSONObject();

Then i tried to fetch some data form firebase in loop and tried to put it in the defined json object and that object in defined json array. below is my code

for(int i = 1; i < 13; i++){
        String str = Integer.toString(i);
        mRef.child("calendar").child(str).child("start_date").addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                start_date = dataSnapshot.getValue().toString();

                try {
                    obj.put("start_date", start_date);
                } catch (JSONException e) {
                    e.printStackTrace();
                }

                Log.d("start_date", start_date);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
        mRef.child("calendar").child(str).child("end_date").addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                end_date = dataSnapshot.getValue().toString();

                try {
                    obj.put("end_date", end_date);
                } catch (JSONException e) {
                    e.printStackTrace();
                }

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
        Log.d("obje", "" + obj);
        array.put(obj);

    }

    Log.d("arrary", "" + array);

But when I log my array or object it shows empty. Below is a log of json object of a single loop. D/obje: {} and this is my array after loop. D/arrary: [{},{},{},{},{},{},{},{},{},{},{},{}]

But when I log my object inside onDataChange class it logs data. but when I log at the end of loop it shows empty.

And this is log of start date to show that data is comming from firebase D/start_date: 09/17/2016

Muthukrishnan Rajendran · Accepted Answer · 2017-08-15 12:02:19Z

1

The problem is you are trying to get the value from the asynchronous callback. You're for loop will end before you get the callback from asynchronous request so it's showing empty.

Try like this,

for(int i = 1; i < 13; i++){
    String str = Integer.toString(i);
    mRef.child("calendar").child(str).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            String start_date = (String) dataSnapshot.child("start_date").getValue();
            String end_date = (String) dataSnapshot.child("end_date").getValue();

            try {

                JSONObject jsonObject = new JSONObject();
                jsonObject.put("start_date", start_date);
                jsonObject.put("end_date", end_date);

                Log.d("obje", "" + jsonObject);

                array.put(jsonObject);

            } catch (JSONException e) {
                e.printStackTrace();
            }

            Log.d("start_date", start_date);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

edited Aug 15, 2017 at 12:02

answered Aug 15, 2017 at 11:37

Muthukrishnan Rajendran

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6 Comments

Anil Shrestha Over a year ago

i am new in android can you please explain it in detail and what could be done.

Muthukrishnan Rajendran Over a year ago

You don't need to call 2 times one time itself you can get the complete list of your object using your Model class, check this reference

Anil Shrestha Over a year ago

Thanks for short and new way but when i log my json array after for loop it still returns empty and when i log my json array instde try method it returns all the data form calendar 12 times.

Muthukrishnan Rajendran Over a year ago

yes, I mentioned that only you will get callback only after asynchronous callback ends. your for loop will ends much before that, so your array will be empty that time

Muthukrishnan Rajendran Over a year ago

You know the size already so, after you got the size you can proceed for next step instead of after for loop

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