我之前写了一篇RecyclerView分页加载机制的文章，是基于Android官方的AsyncListUtil实现的，详情见附录文章1。现在再介绍一种RecyclerView分页加载框架：Android Paging Library。
Android Paging Library是Android官方support-v7支持包中专门做的分页框架，详细文档见谷歌官方文档附录2页面。我写这篇文章时候Paging Library的版本是1.0.0-alpha3。
使用Android Paging Library首先需要在gradle添加引用：

implementation 'android.arch.paging:runtime:1.0.0-alpha3'

下面我写示例代码做一个简单的演示：

package zhangphil.demo;import android.arch.paging.PagedList;
import android.arch.paging.PagedListAdapter;
import android.arch.paging.TiledDataSource;
import android.graphics.Color;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.recyclerview.extensions.DiffCallback;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.text.TextUtils;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Executor;public class MainActivity extends AppCompatActivity {private PagedList<DataBean> mPagedList;private MyDataSource mDataSource;private RecyclerView mRecyclerView;private PagedListAdapter mAdapter;private LinearLayoutManager mLayoutManager;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mDataSource = new MyDataSource();makePageList();mRecyclerView = findViewById(R.id.recycler_view);mLayoutManager = new LinearLayoutManager(this);mLayoutManager.setOrientation(LinearLayout.VERTICAL);mRecyclerView.setLayoutManager(mLayoutManager);mAdapter = new MyAdapter();mRecyclerView.setAdapter(mAdapter);mAdapter.setList(mPagedList);mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {private int lastPos;@Overridepublic void onScrollStateChanged(RecyclerView recyclerView, int newState) {super.onScrollStateChanged(recyclerView, newState);lastPos = mLayoutManager.findLastVisibleItemPosition();mPagedList.loadAround(lastPos);//触发Android Paging的加载事务逻辑。}});}private void makePageList() {PagedList.Config mPagedListConfig = new PagedList.Config.Builder().setPageSize(3) //分页数据的数量。在后面的DataSource之loadRange中，count即为每次加载的这个设定值。.setPrefetchDistance(5) //初始化时候，预取数据数量。.setEnablePlaceholders(false).build();mPagedList = new PagedList.Builder().setConfig(mPagedListConfig).setDataSource(mDataSource).setMainThreadExecutor(new BackgroundThreadTask()) //初始化阶段启用.setBackgroundThreadExecutor(new MainThreadTask()) //初始化阶段启动.build();}private class BackgroundThreadTask implements Executor {public BackgroundThreadTask() {this.execute(new Runnable() {@Overridepublic void run() {Log.d("BackgroundThreadTask", "run");}});}@Overridepublic void execute(@NonNull Runnable runnable) {runnable.run();}}private class MainThreadTask implements Executor {public MainThreadTask() {this.execute(new Runnable() {@Overridepublic void run() {Log.d("MainThreadTask", "run");}});}@Overridepublic void execute(@NonNull Runnable runnable) {runnable.run();}}private class MyDataSource extends TiledDataSource<DataBean> {@Overridepublic int countItems() {return TiledDataSource.COUNT_UNDEFINED;}/*** 注意，这里需要后台线程化。** @param startPosition* @param count* @return*/@Overridepublic List<DataBean> loadRange(int startPosition, int count) {Log.d("MyDataSource", "loadRange:" + startPosition + "," + count);List<DataBean> list = loadData(startPosition, count);return list;}}/*** 假设这里需要做一些后台线程的数据加载任务。** @param startPosition* @param count* @return*/private List<DataBean> loadData(int startPosition, int count) {List<DataBean> list = new ArrayList();for (int i = 0; i < count; i++) {DataBean data = new DataBean();data.id = startPosition + i;data.content = "zhangphil@" + data.id;list.add(data);}return list;}private class MyViewHolder extends RecyclerView.ViewHolder {public TextView text1;public TextView text2;public MyViewHolder(View itemView) {super(itemView);text1 = itemView.findViewById(android.R.id.text1);text1.setTextColor(Color.RED);text2 = itemView.findViewById(android.R.id.text2);text2.setTextColor(Color.BLUE);}}private class MyAdapter extends PagedListAdapter<DataBean, MyViewHolder> {public MyAdapter() {super(mDiffCallback);}@Overridepublic MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {View view = LayoutInflater.from(getApplicationContext()).inflate(android.R.layout.simple_list_item_2, null);MyViewHolder holder = new MyViewHolder(view);return holder;}@Overridepublic void onBindViewHolder(MyViewHolder holder, int position) {DataBean data = mPagedList.get(position);holder.text1.setText(String.valueOf(position));holder.text2.setText(String.valueOf(data.content));}}private DiffCallback<DataBean> mDiffCallback = new DiffCallback<DataBean>() {@Overridepublic boolean areItemsTheSame(@NonNull DataBean oldItem, @NonNull DataBean newItem) {Log.d("DiffCallback", "areItemsTheSame");return oldItem.id == newItem.id;}@Overridepublic boolean areContentsTheSame(@NonNull DataBean oldItem, @NonNull DataBean newItem) {Log.d("DiffCallback", "areContentsTheSame");return TextUtils.equals(oldItem.content, newItem.content);}};private class DataBean {public int id;public String content;}
}

代码实现的功能很简单，当RecyclerView不断下滑时，就触发分页加载，把RecyclerView后续使用的数据分页加载显示出来。暂时我将现阶段对Android Paging Library技术的心得记录下来，作为我学习Android Paging Library技术的阶段性备忘录。这部分代码还有待进一步完善，Android Paging Library技术细节后续会继续跟进研究。

附录：
1，《基于Android官方AsyncListUtil优化改进RecyclerView分页加载机制（一）》链接：http://blog.csdn.net/zhangphil/article/details/78603499 
2，谷歌Android官方Android Paging Library技术文档主页：https://developer.android.google.cn/topic/libraries/architecture/paging.html#classes