안드로이드 – 자바 페이징 구현

안드로이드 자바 앱에서 페이징을 구현하는 방법을 설명합니다.
10년 전부터 있었던 구닥다리 기법이지만, 아직 쓸만합니다.

Entity

Item.java

@Entity(tableName = "items")
public class Item {
    @PrimaryKey(autoGenerate = true)
    private int id;
    private String title;
    private String description;

    // Getters and Setters
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getTitle() { return title; }
    public void setTitle(String title) { this.title = title; }
    public String getDescription() { return description; }
    public void setDescription(String description) { this.description = description; }
}

Dao

ItemDao.java

@Dao
public interface ItemDao {
    @Query("SELECT * FROM items ORDER BY id LIMIT :limit OFFSET :offset")
    List<Item> getItemsWithPaging(int limit, int offset);

    @Query("SELECT COUNT(*) FROM items")
    int getTotalCount();

    @Insert
    void insert(Item item);
}

Adapter

ItemAdapter.java

public class ItemAdapter extends RecyclerView.Adapter<ItemAdapter.ItemViewHolder> {
    private List<Item> items = new ArrayList<>();

    @NonNull
    @Override
    public ItemViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_layout, parent, false);
        return new ItemViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ItemViewHolder holder, int position) {
        Item item = items.get(position);
        holder.titleTextView.setText(item.getTitle());
        holder.descriptionTextView.setText(item.getDescription());
    }

    @Override
    public int getItemCount() {
        return items.size();
    }

    public void addItems(List<Item> newItems) {
        int startPosition = items.size();
        items.addAll(newItems);
        notifyItemRangeInserted(startPosition, newItems.size());
    }

    public void clearItems() {
        items.clear();
        notifyDataSetChanged();
    }

    static class ItemViewHolder extends RecyclerView.ViewHolder {
        TextView titleTextView;
        TextView descriptionTextView;

        ItemViewHolder(View itemView) {
            super(itemView);
            titleTextView = itemView.findViewById(R.id.titleTextView);
            descriptionTextView = itemView.findViewById(R.id.descriptionTextView);
        }
    }
}

MainActivity

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private ItemAdapter adapter;
    private ItemDao itemDao;
    private static final int PAGE_SIZE = 20;
    private int currentPage = 0;
    private boolean isLoading = false;
    private boolean isLastPage = false;

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

        RecyclerView recyclerView = findViewById(R.id.recyclerView);
        adapter = new ItemAdapter();
        recyclerView.setAdapter(adapter);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        // Room 데이터베이스 초기화
        AppDatabase db = Room.databaseBuilder(getApplicationContext(),
                AppDatabase.class, "database-name").build();
        itemDao = db.itemDao();

        // 스크롤 리스너 설정
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int visibleItemCount = layoutManager.getChildCount();
                int totalItemCount = layoutManager.getItemCount();
                int firstVisibleItemPosition = layoutManager.findFirstVisibleItemPosition();

                if (!isLoading && !isLastPage) {
                    if ((visibleItemCount + firstVisibleItemPosition) >= totalItemCount
                            && firstVisibleItemPosition >= 0) {
                        loadMoreItems();
                    }
                }
            }
        });

        // 초기 데이터 로드
        loadMoreItems();
    }

    private void loadMoreItems() {
        isLoading = true;

        new Thread(() -> {
            int offset = currentPage * PAGE_SIZE;
            List<Item> newItems = itemDao.getItemsWithPaging(PAGE_SIZE, offset);
            int totalCount = itemDao.getTotalCount();

            runOnUiThread(() -> {
                if (newItems.size() < PAGE_SIZE) {
                    isLastPage = true;
                }
                adapter.addItems(newItems);
                currentPage++;
                isLoading = false;
            });
        }).start();
    }
}

xml

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

item_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:id="@+id/titleTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="16sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/descriptionTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp" />

</LinearLayout>