基于Android官方Paging Library的RecyclerView分页加载框架
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;
@Override
protected 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;
@Override
public 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() {
@Override
public void run() {
Log.d("BackgroundThreadTask", "run");
}
});
}
@Override
public void execute(@NonNull Runnable runnable) {
runnable.run();
}
}
private class MainThreadTask implements Executor {
public MainThreadTask() {
this.execute(new Runnable() {
@Override
public void run() {
Log.d("MainThreadTask", "run");
}
});
}
@Override
public void execute(@NonNull Runnable runnable) {
runnable.run();
}
}
private class MyDataSource extends TiledDataSource<DataBean> {
@Override
public int countItems() {
return TiledDataSource.COUNT_UNDEFINED;
}
/**
* 注意，这里需要后台线程化。
*
* @param startPosition
* @param count
* @return
*/
@Override
public 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);
}
@Override
public 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;
}
@Override
public 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>() {
@Override
public boolean areItemsTheSame(@NonNull DataBean oldItem, @NonNull DataBean newItem) {
Log.d("DiffCallback", "areItemsTheSame");
return oldItem.id == newItem.id;
}
@Override
public 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
