Android Room联合AsyncListUtil实现RecyclerView分页加载ORM数据-阿里云开发者社区

Android Room联合AsyncListUtil实现RecyclerView分页加载ORM数据

我之前写了一系列关于AsyncListUtil实现RecyclerView和ListView的分页加载机制和技术路线，见附录文章4,5。同时也写了一些列文章介绍Android官方推出的ORM数据库：Room技术，见附录文章1,2。现在结合Android分页加载框架AsyncListUtil，以及Android官方ORM数据库Room，实现数据库数据分页加载到RecyclerView里面。
先给出一个例子，实现一个简单功能，在Android Room数据库中增加一批数据，然后在RecyclerView滚动时候，触发分页加载逻辑，把数据库中的数据分页分段的加载出来，本例中存储的数据为User。
MainActivity.java：

package zhangphil.demo;

import android.arch.persistence.room.Room;
import android.os.SystemClock;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.util.AsyncListUtil;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
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.List;

public class MainActivity extends AppCompatActivity {
    private final String TAG = "输出";

    private RecyclerView.Adapter mAdapter;
    private LinearLayoutManager mLinearLayoutManager;
    private AsyncListUtil<User> mAsyncListUtil;

    private final int LIMIT = 10;

    private UserDatabase mUserDatabase;
    private UserDao mUserDao;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mUserDatabase = Room.databaseBuilder(getApplicationContext(), UserDatabase.class, "users").build();
        mUserDao = mUserDatabase.getUserDao();

        setContentView(R.layout.activity_main);

        RecyclerView mRecyclerView = findViewById(R.id.recycler_view);

        mLinearLayoutManager = new LinearLayoutManager(this);
        mLinearLayoutManager.setOrientation(LinearLayout.VERTICAL);
        mRecyclerView.setLayoutManager(mLinearLayoutManager);

        mAdapter = new MyAdapter();
        mRecyclerView.setAdapter(mAdapter);

        MyViewCallback mViewCallback = new MyViewCallback();
        MyDataCallback mDataCallback = new MyDataCallback();
        mAsyncListUtil = new AsyncListUtil<>(User.class, LIMIT, mDataCallback, mViewCallback);

        mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                Log.d(TAG + "onScrollStateChanged", "onRangeChanged");
                mAsyncListUtil.onRangeChanged();
            }
        });

        findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG + "刷新", "refresh");
                mAsyncListUtil.refresh();
            }
        });

        findViewById(R.id.add_data).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        writeDatabase();
                    }
                }).start();
            }
        });

        //主动刷新数据。
        new Thread(new Runnable() {
            @Override
            public void run() {
                SystemClock.sleep(500);
                mAsyncListUtil.refresh();
            }
        }).start();
    }

    private class MyDataCallback extends AsyncListUtil.DataCallback<User> {

        @Override
        public int refreshData() {
            //更新数据的元素个数。
            Log.d(TAG + "refreshData", Integer.MAX_VALUE + "");
            return Integer.MAX_VALUE;
        }

        /**
         * 在这里完成耗时的数据加载的耗时任务。
         *
         * @param data
         * @param startPosition
         * @param itemCount
         */
        @Override
        public void fillData(User[] data, int startPosition, int itemCount) {
            Log.d(TAG + "fillData", startPosition + " , " + itemCount);

            List<User> list = mUserDao.getUserWhereUserIdBigThan(startPosition, itemCount);
            for (int i = 0; i < list.size(); i++) {
                data[i] = list.get(i);
            }
        }
    }

    private class MyViewCallback extends AsyncListUtil.ViewCallback {

        @Override
        public void getItemRangeInto(int[] outRange) {
            outRange[0] = mLinearLayoutManager.findFirstVisibleItemPosition();
            outRange[1] = mLinearLayoutManager.findLastVisibleItemPosition();

            Log.d(TAG + "getItemRangeInto", outRange[0] + " ~ " + outRange[1]);
        }

        @Override
        public void onDataRefresh() {
            mAdapter.notifyItemRangeChanged(mLinearLayoutManager.findFirstVisibleItemPosition(), LIMIT);
            Log.d(TAG + "onDataRefresh", mLinearLayoutManager.findFirstVisibleItemPosition() + "," + mLinearLayoutManager.findLastVisibleItemPosition());
        }

        @Override
        public void onItemLoaded(int position) {
            mAdapter.notifyItemChanged(position);
            Log.d(TAG + "onItemLoaded", String.valueOf(position));
        }
    }

    private class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
        public MyAdapter() {
            super();
        }

        @Override
        public MyViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
            View view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.item_layout, viewGroup, false);
            MyViewHolder holder = new MyViewHolder(view);
            return holder;
        }

        @Override
        public void onBindViewHolder(MyViewHolder viewHolder, int i) {
            User u = mAsyncListUtil.getItem(i);
            viewHolder.setData(u);
        }

        @Override
        public int getItemCount() {
            return mAsyncListUtil.getItemCount();
        }
    }

    private class MyViewHolder extends RecyclerView.ViewHolder {
        public TextView userId;
        public TextView userName;
        public TextView userAge;

        public MyViewHolder(View itemView) {
            super(itemView);

            userId = itemView.findViewById(R.id.user_id);
            userName = itemView.findViewById(R.id.user_name);
            userAge = itemView.findViewById(R.id.user_age);
        }

        public void setData(User u) {
            if (u != null) {
                userId.setText("id:" + String.valueOf(u.userId));
                userName.setText("姓名:" + String.valueOf(u.name));
                userAge.setText("年龄:" + String.valueOf(u.age));
            }
        }
    }

    private void writeDatabase() {
        Log.d(TAG + "writeDatabase", "开始写入数据...");
        for (int i = 0; i < 100; i++) {
            User user = new User();
            user.name = "张" + i;
            user.age = (int) (Math.random() * 100);
            user.updateTime = System.currentTimeMillis();

            mUserDao.insertUser(user);
        }
        Log.d(TAG + "writeDatabase", "写入数据库完毕.");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mUserDatabase.close();
    }
}

MainActivity需要的布局文件activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="更新" />

    <Button
        android:id="@+id/add_data"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="添加数据" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

item_layout.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="20dp">

    <TextView
        android:id="@+id/user_id"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@android:color/holo_red_light" />

    <TextView
        android:id="@+id/user_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="@android:color/holo_orange_light" />

    <TextView
        android:id="@+id/user_age"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="@android:color/holo_blue_light" />

    <View
        android:layout_width="match_parent"
        android:layout_height="1px"
        android:background="@android:color/darker_gray" />
</LinearLayout>

涉及到Android Room的Model，表，Dao。
User.java：

package zhangphil.demo;

import android.arch.persistence.room.ColumnInfo;
import android.arch.persistence.room.Entity;
import android.arch.persistence.room.PrimaryKey;

/**
 * Created by Phil on 2017/11/22.
 */

@Entity(tableName = "user_table")
public class User {
    @PrimaryKey(autoGenerate = true)
    public int userId;

    @ColumnInfo(name = "userName")
    public String name;

    @ColumnInfo(name = "userAge")
    public int age = -1;

    @ColumnInfo(name = "updateTime")
    public long updateTime = -1;
}

UserDao.java：

package zhangphil.demo;

import android.arch.persistence.room.Dao;
import android.arch.persistence.room.Delete;
import android.arch.persistence.room.Insert;
import android.arch.persistence.room.OnConflictStrategy;
import android.arch.persistence.room.Query;
import android.arch.persistence.room.Update;

import java.util.List;

/**
 * Created by Phil on 2017/11/22.
 */

@Dao
public interface UserDao {
    @Query("SELECT * FROM user_table")
    public List<User> getAllUsers();

    @Query("SELECT * FROM user_table WHERE userId >:uid ORDER BY userId ASC LIMIT :limit")
    public List<User> getUserWhereUserIdBigThan(int uid, int limit);

    @Query("SELECT * FROM user_table WHERE userId =:uid")
    public List<User> getUserWhereUserIdEqual(int uid);

    @Query("SELECT * FROM user_table WHERE userId BETWEEN :minId AND :maxId  ORDER BY userId ASC")
    public List<User> getUserIdBetween(int minId, int maxId);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    public void insertUser(User... users);

    @Update
    public void updateUser(User... users);

    @Delete
    public void deleteUser(User... users);
}

UserDatabase.java：

package zhangphil.demo;

import android.arch.persistence.room.Database;
import android.arch.persistence.room.RoomDatabase;

/**
 * Created by Phil on 2017/11/22.
 */

@Database(entities = {User.class}, version = 1, exportSchema = false)
public abstract  class UserDatabase  extends RoomDatabase {
    public abstract UserDao getUserDao();
}

代码运行结果，初始化：

当点击“添加数据”添加完数据库数据后，点击“更新”按钮后：

小结：
（一）在本例中，使用Android Room获得分页数据时候，和之前的UserDao相比，增加了SQL查询约束LIMIT，关于LIMIT，详情见附录文章3。从SQL取数据时，就事先作为分页，把数据分块，而不像以前那样一次性无脑取出数据库表中的全部数据。从而提高了性能。
（二）AsyncListUtil需要延迟的主动refresh()，才能再初始化后且无滚动RecyclerView时加载出来数据。本例中在MainActivity的onCreate最后，开启一个线程，该线程故意延迟一定时间，然后才启动AsyncListUtil的refresh()。之所以这么做，有部分原因是因为AsyncListUtil和RecyclerView之间，UI绘制和数据的更新没有同步，导致第一次初始化加载后，无法刷出来数据。明显的现象就是：如果数据库中有数据，初次打开整个程序，RecyclerView加载出来的每个item是空的，但是明明此时数据库中有数据，按照道理应该初始化加载出来，但是没有。追踪代码就会发现，导致这一现象发生，极大程度上是AsyncListUtil的回调先于RecyclerView完成初始化，导致onDataRefresh和getItemRangeInto
捕捉和使用的第一个和最后一个RecyclerView可见item position均为-1引起。

附录：
1，《Android官方ORM数据库Room技术解决方案：@Embedded内嵌对象（二）》链接：http://blog.csdn.net/zhangphil/article/details/78621009
2，《Android官方ORM数据库Room技术解决方案简介（一）》链接：http://blog.csdn.net/zhangphil/article/details/78611632
3，《SQL数据库查询LIMIT 数据分页》链接：http://blog.csdn.net/zhangphil/article/details/78653677
4，《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
5，《基于Android官方AsyncListUtil优化经典ListView分页加载机制（二）》链接：http://blog.csdn.net/zhangphil/article/details/78645089

Android Room联合AsyncListUtil实现RecyclerView分页加载ORM数据

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