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

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 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 {        @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 loadRange(int startPosition, int count) {            Log.d("MyDataSource", "loadRange:" + startPosition + "," + count);            List 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 loadData(int startPosition, int count) {        List 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 {        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 mDiffCallback = new DiffCallback() {        @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

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