Reading from a Firebase Database

Question

I'm trying to read from a Firebase Database, I've read and looked everywhere, but I'm at a dead end.

Here's all that I've done.

Dependencies:

implementation 'com.google.firebase:firebase-storage:9.2.1'

implementation 'com.google.firebase:firebase-database:9.2.1'

implementation 'com.google.firebase:firebase-auth:9.2.1'

implementation 'com.google.firebase:firebase-core:9.2.1'

minSdkVersion: 15

DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();

then in a Button onClick method, I put the listener:

mDatabase.child("List").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                String savedData = dataSnapshot.getValue(String.class);
                Log.d(TAG, "snapshot: " + savedData);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.d(TAG, "Error");
            }
    });

Here is a look at the Database.

Would appreciate the input.

Answer 1

You're trying to read a String value under List . But right under List there's no string value, rather there's a list of objects under there. To get the actual values, you'll need to navigate the JSON structure in your code.

Something like:

DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();
mDatabase.child("List").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot tierSnapshot: dataSnapshot.getChildren()) {
            Log.d(TAG, tierSnapshot.getKey(); // "Tier 1", "Tier 1 B"
            for (DataSnapshot secondSnapshot: tierSnapshot.getChildren()) {
                Log.d(TAG, secondSnapshot.getKey(); // "Tier 2", "Tier 2 B"

                String str = secondSnapshot.getValue(String.class);
                Log.d(TAG, str); // null, "2 B"

                Long num = secondSnapshot.getValue(long.class);
                Log.d(TAG, num); // 2, null

            }
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.w(TAG, "Error", databaseError);
    }
});

An extra thing to note is that your values are of a different type, with the first one being the number 2 , while the second one is a string "2 B" . Hence the two getValue() calls, to get the specific type out of there. You could also just do secondSnapshot.getValue() and deal with the resulting object as you'd usually do (eg call toString() on it).