ListVew doesn't show anything : I try to retrieve data from firebase and use an adapter to show them in listview. 
Everything is ok with retrieving data, I checked through debugger, however nothing is shown.
Here is *resource_layout.xml*

    <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/borders">

    <ListView
        android:id="@+id/listViewBooks"
        android:layout_weight="1"
        android:layout_height="0dp"
        android:layout_width="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true" />
</RelativeLayout>

*resource_item.xml*

    ?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="match_parent"
        android:layout_height="match_parent">
    
            <TextView
                android:id="@+id/name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="TextView" />
    
            <TextView
                android:id="@+id/author"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="TextView" />
    
            <TextView
                android:id="@+id/date"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="TextView" />
    
    </LinearLayout>

*ResourceAdapter.java*

    public class ResourceAdapter extends ArrayAdapter<Books> {
    
        private Activity context;
        private List<Books> bookList;
    
        public ResourceAdapter(Activity context, List<Books> bookList){
            super(context, R.layout.resource_item, bookList);
            this.context = context;
            this.bookList = bookList;
        }
    
        @NonNull
        @Override
        public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    
            LayoutInflater inflater = context.getLayoutInflater();
            View listViewItem = inflater.inflate(R.layout.resource_item, null, true);
    
            TextView textViewName = (TextView) listViewItem.findViewById(R.id.name);
            TextView textViewAuthor = (TextView) listViewItem.findViewById(R.id.author);
            TextView textViewDate = (TextView) listViewItem.findViewById(R.id.date);
    
            Books book = bookList.get(position);
            textViewName.setText(book.getName());
            textViewAuthor.setText(book.getAuthor());
            textViewDate.setText(String.valueOf(book.getDate()));
    
            return listViewItem;
        }
    }

*Resource.Java*

    public class Resource extends AppCompatActivity {
    
        DatabaseReference databaseBooks;
        ListView listViewBooks;
        List<Books> bookList;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.resource_layout);
    
            databaseBooks = FirebaseDatabase.getInstance().getReference("books");
    
            bookList = new ArrayList<>();
    
            listViewBooks = (ListView) findViewById(R.id.listViewBooks);
    
        }
    
        @Override
        protected void onStart() {
            super.onStart();
    
            databaseBooks.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
    
                    bookList.clear();
    
                    for (DataSnapshot bookSnapshot : dataSnapshot.getChildren()){
                        Books book = bookSnapshot.getValue(Books.class);
                        bookList.add(book);
                    }
    
                    ResourceAdapter adapter = new ResourceAdapter(Resource.this, bookList);
                    listViewBooks.setAdapter(adapter);
    
                }
    
                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
        }
    }