Retrieving data from Firebase in Android activity

user_5829826 0
Viewed 811

I read many threads regarding how to get data from Firebase database instance, but none of them worked for me.

My code in the activity:

public class Violations extends AppCompatActivity
{
TextView textView7;

FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference dbref = database.getReference("save");

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

    textView7 = findViewById(R.id.textView7);

    dbref.addValueEventListener(new ValueEventListener()
    {
        ArrayList<String> Violations = new ArrayList<>();
        @Override
        public void onDataChange(DataSnapshot dataSnapshot)
        {
            for (DataSnapshot postSnapshot: dataSnapshot.getChildren())
            {
                Violations.add(postSnapshot.getValue().toString());
                System.out.println(postSnapshot.getValue().toString());
            }
            for(int i=0; i < Violations.size(); i++)
            {
                textView7.setText(textView7.getText() + Violations.get(i) + System.lineSeparator());
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {}
    });
}
}

There is no error in there, but no data displays. I am pretty sure, my problem is connecting to the right instance and retrieving the data.

Firebase data, are like this:

enter image description here

Can someone please help me in there?

Thanks you in advance.

firebase-realtime-database firebase android java
3 Answers

Initialize the Firebase database & the DatabaseReference inside onCreate() method:

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

    FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference dbref = database.getReference("save");

    ...
    ..

Also, the reference you are getting is save but the Firebase database shows that is : you violate .... You may try changing the name to save or getting the right data : you violate ....

user_44091130

Try to use addListenerForSingleValue() instead of addValueEventListener(). Hope it helps. And change your firebase link save to you violate your own speed limit with

user_103833790

I cannot see in your database schema o reference named save but I see one named You violate your own speed limit with, which mush be used in your reference in order to be able to get data from the database. So to solve this, please use the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = rootRef.child("You violate your own speed limit with");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        ArrayList<String> violations = new ArrayList<>();
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String speed = ds.getValue(String.class);
            violations.add(speed);
            Log.d(TAG, speed);
        }

        //Do what you need to do with y our violations list
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage());
    }
};
ref.addListenerForSingleValueEvent(valueEventListener);

The result in your logcat will be all those values:

3 km / h at time: ...
3 km / h at time: ...
//an so on
user_52468850
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