안드로이드 페이징 라이브러리가 무한 스크롤을 할 때 더 많은 항목을 요청하는 경우

Question

아키텍처 구성 요소의 새로운 android Paging Library을 사용하여 더 많은 항목을 서버에 요청하는 방법을 아는 방법? 예를 들어 서버에서 데이터가로드되는 끝없는 스크롤을 구현하려는 경우 어떻게하면 더 많은 항목을 요청해야하는지 알 수 있습니다.

Answer 1

나는이 기능을 구현하기위한 다음 클래스를 사용

package com.mlsdev.enjoymusic.data.repository; 

import android.arch.paging.DataSource; 
import android.arch.paging.TiledDataSource; 
import android.arch.persistence.room.InvalidationTracker; 
import android.support.annotation.NonNull; 
import android.support.annotation.WorkerThread; 
import android.util.Log; 

import com.mlsdev.enjoymusic.data.local.DeezerDatabase; 
import com.mlsdev.enjoymusic.data.local.Table; 

import java.io.IOException; 
import java.util.List; 
import java.util.Set; 

import retrofit2.Call; 
import retrofit2.Response; 

/** 
* Created by stafievsky on 09.10.17. 
*/ 

public abstract class PagedNetworkBoundResource<ResultType, RequestType> extends TiledDataSource<ResultType> { 

    private final InvalidationTracker.Observer mObserver; 
    private DeezerDatabase db; 

    public PagedNetworkBoundResource(DeezerDatabase db) { 
     this.db = db; 
     mObserver = new InvalidationTracker.Observer(Table.States.PLAY_STATE) { 

      public void onInvalidated(@NonNull Set<String> tables) { 
       invalidate(); 
      } 
     }; 
     this.db.getInvalidationTracker().addWeakObserver(mObserver); 
    } 


    @Override 
    public boolean isInvalid() { 
     db.getInvalidationTracker().refreshVersionsSync(); 
     return super.isInvalid(); 
    } 

    @Override 
    public int countItems() { 
     return DataSource.COUNT_UNDEFINED; 
    } 

    @Override 
    public List<ResultType> loadRange(int startPosition, int count) { 
     if (startPosition == 0 && count == 20) { 
      clearDB(); 
     } 
     fetchFromNetwork(startPosition, count); 
     return loadFromDb(startPosition, count); 
    } 

    public abstract void clearDB(); 

    @WorkerThread 
    private void fetchFromNetwork(int startPosition, int count) { 
     if (createCall(startPosition, count) != null) 
      try { 
       Response<RequestType> response = createCall(startPosition, count).execute(); 
       if (response.isSuccessful() && response.code() == 200) { 
        saveCallResult(response.body()); 
       } 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } 
    } 

    @WorkerThread 
    protected abstract void saveCallResult(@NonNull RequestType item); 


    @WorkerThread 
    protected abstract List<ResultType> loadFromDb(int startPosition, int count); 

    @WorkerThread 
    protected abstract Call<RequestType> createCall(int startPosition, int count); 
} 

그리고이 클래스의 구현 :

public LiveData<PagedList<ChartAlbumDao.Album>> getAlbums() { 

    return new LivePagedListProvider<Integer, ChartAlbumDao.Album>() { 
     @Override 
     protected DataSource<Integer, ChartAlbumDao.Album> createDataSource() { 
      return new PagedNetworkBoundResource<ChartAlbumDao.Album, ModelList<ChartAlbumEntity>>(db) { 

       @Override 
       public void clearDB() { 

       } 

       @Override 
       protected void saveCallResult(@NonNull ModelList<ChartAlbumEntity> item) { 
        if (item != null) { 
         chartAlbumDao.saveAlbums(item.getItems()); 
        } 
       } 

       @NonNull 
       @Override 
       protected List<ChartAlbumDao.Album> loadFromDb(int startPosition, int count) { 
        return chartAlbumDao.loadAlbums(count, startPosition); 
       } 

       @NonNull 
       @Override 
       protected Call<ModelList<ChartAlbumEntity>> createCall(int startPosition, int count) { 
        return deezerService.getChartAlbums(startPosition, count); 
       } 
      }; 
     } 

    }.create(0, new PagedList.Config.Builder() 
      .setEnablePlaceholders(false) 
      .setPageSize(20) 
      .setInitialLoadSizeHint(20) 
      .build()); 
}