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

「爱情、让人受尽委屈。」 2024-02-18 16:42 20阅读 0赞

**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