Android Room联合AsyncListUtil实现RecyclerView分页加载ORM数据

小灰灰 2024-02-18 16:47 13阅读 0赞

**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：  
![Center][]  
  
  
  
当点击“添加数据”添加完数据库数据后，点击“更新”按钮后：  
![Center 1][]  
  
  
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

[Center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/bde5a77d94d64f24960d8936f3d89481.png
[Center 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/e95af5c6d90c476c9d2523f91fc7a299.png