How to save retrieved data from firebase to string variable in android?

Question

Hy Developers, I am new to android development so that's why facing an issue in saving and viewing data to my android app.

I know that data can only be retrieved while you are connected to internet.

But the thing is it is retrieving data and also showing to android log.

But when i try to save it to a string variable or to arraylist to show it on main activity using that list or variable, its not working.

I am declaring a private string variable to store value from firebase database before onCreate method.

Sorry for my nob question. But this is the issue i am facing.

Following is the code that i am using and some screenshots to make the question understandable.

public class MainActivity extends AppCompatActivity {

private static final String TAG = "Firelog" ;

Button ans1, ans2, ans3, ans4;

TextView uscore, question, timer;

private String mAnswer;

private ArrayList<String> fbquestions = new ArrayList<String>();

private String quest;

private int mScore = 0;

Random r = new Random();

private int res = 0;

private int c = 0;

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

    uscore = (TextView) findViewById(R.id.uscore);
    question = (TextView) findViewById(R.id.question);
    timer = (TextView) findViewById(R.id.timer);

    ans1 = (Button) findViewById(R.id.ans1);
    ans2 = (Button) findViewById(R.id.ans2);
    ans3 = (Button) findViewById(R.id.ans3);
    ans4 = (Button) findViewById(R.id.ans4);

    FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference myRef = database.getReference("mcqs");

    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Map <String, String> map = (Map)dataSnapshot.getValue();
            quest = map.get("question");

            fbquestions.add(quest);

            Log.v("E_Value","Question is" + quest);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

    question.setText(String.valueOf(fbquestions.get(0)));
  }
}

In above pic you can see that question is retrieved successfully from firebase and visible in log.

But here when i try to display question on main screen after assigning, its showing blank.

After adding the code to add value to arraylist, application crashes..

I am doing that, you can see this in the code i provided above.. — Ahsan Ellahi, Sep 16 '18 at 12:53
check answer @Ehsan and let me know one thing are you getting value in logs.? — Atif AbbAsi, Sep 16 '18 at 12:54
Yes as you could see in the black picture above, i am getting the question in log "What is your name" — Ahsan Ellahi, Sep 16 '18 at 12:58
question.setText(String.valueOf(fbquestions.get(0))); why you are doing this.? — Atif AbbAsi, Sep 16 '18 at 13:22

score 1 · Accepted Answer · answered Sep 16 '18 at 13:21

1

You cannot simply get the value of fbquestions.get(0) outside the onDataChange() method because this method has an asynchronous behavior. So you cannot simply create your fbquestions list as a global variable and use it's value outside the callbakc because it will always be empty. Basically, you're trying to use a value synchronously from an API that's asynchronous. That's not a good idea. You should handle the APIs asynchronously as intended.

A quick solve for this problem would be to move the following line of code:

question.setText(String.valueOf(fbquestions.get(0)));

Inside the callback right after this line of code:

Log.v("E_Value","Question is" + quest);

And your problem will be solved. If you want to use the list outside, I recommend you see the last part of my anwser from this post in which I have explained how it can be done using a custom callback. You can also take a look at this video for a better understanding.

answered Sep 16 '18 at 13:21

Alex Mamo

130,605
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Perfectly got the solution. But there is a little issue again. I want to use that list to display values on main screen after it had finished adding all elements to the list from firebase db. – Ahsan Ellahi Sep 16 '18 at 14:14
1

Oh, it's pretty simple. **[This](https://stackoverflow.com/questions/48622480/showing-firebase-data-in-listview)** is a recommended way in which you can retrieve data from a Firebase Realtime database and display it in a `ListView` using an `ArrayAdapter` and **[this](https://stackoverflow.com/questions/49383687/how-can-i-retrieve-data-from-firebase-to-my-adapter/49384849)** is a recommended way in which you can retrieve data from a Firebase Realtime database and display it in a `RecyclerView` using `FirebaseRecyclerAdapter`. – Alex Mamo Sep 16 '18 at 14:18
I know that we can use list view or Recyclerview. But that's for list items. I want to show a single question from my list to the main screen using a random number. I am working on a quiz app. – Ahsan Ellahi Sep 16 '18 at 14:19
This sounds as another question but since I have already answered a similar one, **[here](https://stackoverflow.com/questions/50413117/how-to-get-unique-random-product-in-node-firebase/50413208)** is how you can get a random item from a section of your database. – Alex Mamo Sep 16 '18 at 14:21
You have references in all those answers so you can generate a random item and display it in a `RecyclerView` or `ListView`. So given the information in those answers, please make your own attempt and ask another question if something else comes up. Cheers! – Alex Mamo Sep 16 '18 at 14:25

Atif AbbAsi · Answer 2 · 2018-09-16T12:59:22.560

0

Pass quest value to Textview..

ArrayList<String> questionArrrayList =new Arraylist<>();
questionArrrayList .clear();

   myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Map <String, String> map = (Map)dataSnapshot.getValue();
            quest = map.get("question");
             question.setText(quest);


                questionArrrayList .add(quest);
                Log.v("E_Value","Question is" + quest);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

edited Sep 16 '18 at 12:59

answered Sep 16 '18 at 12:53

Atif AbbAsi

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that would work i know, but i want to save questions.. So later on i can view that on main screen using get function of arraylist. – Ahsan Ellahi Sep 16 '18 at 12:57
then store that Question in arrayList – Atif AbbAsi Sep 16 '18 at 12:57
This code is useful, but this will only display the current retrieved value to the main screen. – Ahsan Ellahi Sep 16 '18 at 12:59
what you actually want to do.? – Atif AbbAsi Sep 16 '18 at 12:59
I have mcqs in my db, i want to retrieve each question from db and to store them in arraylist so i could show them to user by generating random numbers. – Ahsan Ellahi Sep 16 '18 at 13:00
do one thing store data in list and check log for that arraylist – Atif AbbAsi Sep 16 '18 at 13:02
please check the code again, i updated it and now application get crashed. – Ahsan Ellahi Sep 16 '18 at 13:10
kindly share crash logs. and post your code of array list – Atif AbbAsi Sep 16 '18 at 13:20

How to save retrieved data from firebase to string variable in android?

2 Answers2