android paging组件的理解

import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.ViewModel;
import android.arch.paging.LivePagedListBuilder;
import android.arch.paging.PagedList;

public class ConcertViewModel extends ViewModel {

    private static final int PAGE_SIZE = 10;//初始加载数量
    private static final int RELOAD_SIZE = 20;//往下滑动加载数量

    private final LiveData<PagedList<Concert>> mConcertListLiveData;

    public ConcertViewModel() {
        PagedList.Config config = new PagedList.Config.Builder()
                .setPageSize(PAGE_SIZE) // 分页加载的数量
                .setEnablePlaceholders(false) // 当item为null是否使用PlaceHolder展示
                .setInitialLoadSizeHint(RELOAD_SIZE) // 预加载的数量, 与分页加载的数量成倍数关系
                .setPrefetchDistance(5) //设置距离最后还有多少个item时，开始加载下一页的数据.
                .build();


        mConcertListLiveData = new LivePagedListBuilder<>(new ConcertFactory(), config)
                .setBoundaryCallback(new ConcertListBoundaryCallback())
                .build();
    }

    public LiveData<PagedList<Concert>> getConcertListLiveData() {
        return mConcertListLiveData;
    }
}