使用 Firebase 中的数据创建 Listview

Question

I should see in all the "Incontro" field that are in my database (They are events to understand us), see with the user who is logged in at that moment which of these events participates, his Id is in Incontro -> 123123... .-> "Participants" -> "here the id". Basically I have to create a listview of all the events that participates and show in the list the various data of that event. How can I do? I put below the code that I managed to do but when I start nothing appears.

Database example: https://imgur.com/a/dD4sTFn

public class ListaIncontriFragment extends AppCompatActivity {
    
    ListView listView;
    ArrayList<String> arrayList = new ArrayList<>();
    ArrayAdapter<String> arrayAdapter;
    private List<Incontro> Incontri;

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

    String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();

    Incontri = new ArrayList<>();
    listView=(ListView) findViewById(R.id.list_view);
    arrayAdapter= new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,arrayList);
    listView.setAdapter(arrayAdapter);

        for(Incontro incontro : Incontri) {

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Incontro")
                    .child(incontro.getIncontroidId())
                    .child("Partecipanti");
            DatabaseReference uidRef = reference.child(uid);

            ValueEventListener valueEventListener = new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    if (dataSnapshot.exists()) {
                        String value = dataSnapshot.getValue(Incontro.class).toString();

                        arrayList.add(value);
                        arrayAdapter.notifyDataSetChanged();

                        

                    }
                }

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

        }
    }



}

Answer 1

So it would be a good idea to paste your ArrayAdapter code as well. A few steps to solve this:

1. In your ArrayAdapter class, I'd verify that you've implemented a getItem() method that returns the correct data type from your arrayList.

2. It also wouldn't hurt to add a method to again set the arrayList in your Fragment to your adapter's own list. And do that right before you call notifyDataSetChanged()

3. Worst case, you reinitialize your adapter again before that call to verify your adapter is actually working.