CODEWITHSUNDEEP
javaandroidfirebasefirebase-realtime-database
Ahsan Ellahi
Ahsan Ellahi

Reputation: 55

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

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)));
  }
}

enter image description here

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

enter image description here

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

enter image description here

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

Upvotes: 1

Views: 2597

Answers (2)

Alex Mamo
Alex Mamo

Reputation: 138824

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.

Upvotes: 1

Atif AbbAsi
Atif AbbAsi

Reputation: 6035

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) {

        }
    });

Upvotes: 0

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