如何在 Android 中显示来自 Firebase 的特定子值？

Question

DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("User Allergens").child(uid);

what do i need to add after.child(UID)? the code I have:

    ArrayList<String> list = new ArrayList<>();
    ArrayAdapter adapter = new ArrayAdapter<String>(this, R.layout.list_item, list );
    listView.setAdapter(adapter);

    DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("User Allergens").child(uid);
    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            list.clear();
            for (DataSnapshot snapshot : dataSnapshot.getChildren() ){
                list.add(snapshot.getValue().toString());
            }
            adapter.notifyDataSetChanged();
        }

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

        }
    });

picture of data structure in firebase, have a look for a clear view.

Answer 1

As I see in your screenshot, under the following reference:

FirebaseRoot -> User Allergens -> UID

You have a few children of type String, that contain some values like Lactose , Gluten or Sugar . To get all these values and use them in your adapter, please use the following lines of code:

ListView listView = (ListView) findViewById(R.id.list_view);
List<String> list = new ArrayList<>();
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.list_item, list);
listView.setAdapter(arrayAdapter);
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("User Allergens").child(uid);
uidRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DataSnapshot> task) {
        if (task.isSuccessful()) {
            for (DataSnapshot alergenSnapshot : task.getResult().getChildren()) {
                String alergen = alergenSnapshot.getValue(String.class);
                list.add(alergen);
            }
            adapter.notifyDataSetChanged();
        } else {
            Log.d(TAG, task.getException().getMessage()); //Don't ignore potential errors!
        }
    }
});

If task.getException().getMessage() yelds no errors, then the result of the above code will be a ListView filled up with alergen names from your Firebase Realtime Database.