Showing Firebase Data in Listview

Showing Firebase data in ListView

This is a classic issue with asynchronous APIs. In order to make it work, change your model class according to Java Naming Conventions. Your class should look like this:

public class Score {
    private String userId, score;

    public Score() {}

    public Score(String userId, String score) {
        this.userId = userId;
        this.score = score;
    }

    public String getUserId() {
        return userId;
    }

    public String getScore() {
        return score;
    }

    @Override
    public String toString() {
        return "Score{" +
                "userId='" + userId + '\'' +
                ", score='" + score + '\'' +
                '}';
    }
}

Also note that onDataChange() method has an asynchronous behavior, which means that is called even before you are trying to add those objects of Score class to the list. In other words, your list will always be empty outside that method. A quick fix would be to move the declaration of your list inside onDataChange() and do what you want to do with it or, if you want to dive into the asynchronous world and use my answer from this post.

Assuming the score node is a direct child of your Firebase root, to display the data using the String class, please use the following code:

ListView listView = (ListView) findViewById(R.id.list_view);
List<String> list = new ArrayList<>();
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, list);
listView.setAdapter(arrayAdapter);
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference scoreRef = rootRef.child("score");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String userId = ds.child("userId").getValue(String.class);
            String score = ds.child("score").getValue(String.class);
            list.add(userId + " / " +  score);
            Log.d("TAG", userId + " / " +  score);
        }
        arrayAdapter.notifyDataSetChanged();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.d(TAG, task.getException().getMessage());
    }
};
scoreRef.addListenerForSingleValueEvent(eventListener);

And this how you can display data using the Score class.

ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            Score score = ds.getValue(Score.class);
            String userId = score.getUserId();
            String score = score.getScore();
            Log.d("TAG", userId + " / " +  score);
            list.add(score);
        }
        arrayAdapter.notifyDataSetChanged();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.d(TAG, task.getException().getMessage());
    }
};
scoreRef.addListenerForSingleValueEvent(eventListener);

How to retrieve data from Firebase into a ListView (with custom Array Adapter)

You are getting a "blank screen" because the name of the properties in your class do not match the name of the properties in the database. See, you have a field named mPlaceTitle in your Place class, while in the database is called placeTitle and this is not correct. To solve this, you can simply change the name of all properties in your class to match the one in the database, which are named correct according to the Java Naming Conventions regarding variables.

Show Firebase data in ListView

You didn't add the child reference to your DB.

1.
Use This Line Instead

mDatabase = FirebaseDatabase.getInstance().getReference().child(User).child(Instruktor);

2.
getValue(String.class) will most probably retieve a list of true.

To refer the names within Predmeti you can try getKey()

String []value = subjectssnapshot.child("Predmeti").getValue(String.class);

3.
Use this to update the list
arrayAdapter.notifyDataSetChanged();

How to display the firebase data in listview?

You can use FirebaseListAdapter for display data in list.

Like :

Firebase ref = new Firebase("https://<yourapp>.firebaseio.com");
     ListAdapter adapter = new FirebaseListAdapter<ChatMessage>(this, ChatMessage.class, android.R.layout.two_line_list_item, mRef)
     {
         protected void populateView(View view, ChatMessage chatMessage)
         {
             ((TextView)view.findViewById(android.R.id.text1)).setText(chatMessage.getName());
             ((TextView)view.findViewById(android.R.id.text2)).setText(chatMessage.getMessage());
         }
     };
     listView.setListAdapter(adapter);

Retrieve Firebase Data and Display in ListView in Android Studio

You are getting that error, because you are missing a child. To solve this, please change the following line of code:

String value = dataSnapshot.getValue(String.class);

to

String value = dataSnapshot.child("Name").getValue(String.class);

The output in your logat will be the name of all clients.

P.S. Also be aware that you'll encounter other errors in your project because the name of your fields inside your Client class are all lowercase while in your database all start with a capital letter. The name should be the same. Please also take a look here.

public class Client {
    private String name, location, latitude, longitude;

    public Client() {}

    public Client(String name, String location, String latitude, String longitude) {
        this.name = name;
        this.location = location;
        this.latitude = latitude;
        this.longitude = longitude;
    }

    public String getName() { return name; }
    public String getLocation() { return location; }
    public String getLatitude() { return latitude; }
    public String getLongitude() { return longitude; }
}

How to Read Data from Firebase Database and Display Multiple Fields in ListView with ArrayAdapter

after two days of being stuck I was able to answer my own question! Hopefully this will help future beginners stuck trying to display a custom view within an ArrayAdapter. Basically, I created a custom ArrayAdapter class which could hold three TextViews inside of it.

I am in no means an expert and will not be able to explain this as well as others, so instead, I will paste a link to the two video tutorials that I followed and had success with.

Android Beginner Tutorial #8 - Custom ListView Adapter For Displaying Multiple Columns
https://www.youtube.com/watch?v=E6vE8fqQPTE&t=392s

Android Beginner Tutorial #9 - Custom ListView Adapter [With Loading Animation]
https://www.youtube.com/watch?v=SApBLHIpH8A

Here is my updated code below:

CustomAdapter.java

public class CustomAdapter extends BaseAdapter {

    private static ArrayList<SearchModel> searchArrayList;
    private LayoutInflater mInflater;
    private Context mContext;
    private int lastPosition;

    /**
     * Holds elements in a view
     */
    static class ViewHolder {
        TextView make;
        TextView model;
        TextView stock;
    }

    public CustomAdapter(Context context, ArrayList<SearchModel> results) {
        searchArrayList = results;
        mContext = context;
        mInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return searchArrayList.size();
    }

    @Override
    public Object getItem(int position) {
        return searchArrayList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        String make = searchArrayList.get(position).getMake();
        String model = searchArrayList.get(position).getModel();
        String stock = searchArrayList.get(position).getStock();

        final View result;

        ViewHolder holder;

        if (convertView == null) {

            LayoutInflater inflater = LayoutInflater.from(mContext);
            convertView = inflater.inflate(R.layout.list_item, parent, false);
            holder = new ViewHolder();
            holder.make = (TextView) convertView.findViewById(R.id.tv_list_item_make);
            holder.model = (TextView) convertView.findViewById(R.id.tv_list_item_model);
            holder.stock = (TextView) convertView.findViewById(R.id.tv_list_item_stock);

            result = convertView;
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
            result = convertView;
        }

        Animation animation = AnimationUtils.loadAnimation(mContext,
                (position > lastPosition) ? R.anim.load_down_anim : R.anim.load_up_anim);
        result.startAnimation(animation);
        lastPosition = position;

        holder.make.setText(make);
        holder.model.setText(model);
        holder.stock.setText(stock);

        return convertView;
    }
}

MainActivity.java (Only the onCreate method)

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        databaseReference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                String make = snapshot.child("make").getValue(String.class);
                String model = snapshot.child("model").getValue(String.class);
                String stock = snapshot.child("stock").getValue(Long.class).toString();
                SearchModel searchModel = new SearchModel(make, model, stock);
                searchList.add(searchModel);

              CustomAdapter customAdapter = new CustomAdapter(getApplicationContext(), searchList);

                mListView = (ListView) findViewById(R.id.lv_searches);
                mListView.setAdapter(customAdapter);
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot snapshot) {
            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
            }

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

---

Related Topics