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基于Android官方Paging Library的RecyclerView分页加载框架

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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 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

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