Android Room聯合AsyncListUtil實現RecyclerView分頁載入ORM資料

標籤：添加   .com   最佳化   XML   開啟   res   context   apt   分頁載入   

Android Room聯合AsyncListUtil實現RecyclerView分頁載入ORM資料
我之前寫了一系列關於AsyncListUtil實現RecyclerView和ListView的分頁載入機制和技術路線，見附錄文章4,5。同時也寫了一些列文章介紹Android官方推出的ORM資料庫：Room技術，見附錄文章1,2。現在結合Android分頁載入架構AsyncListUtil，以及Android官方ORM資料庫Room，實現資料庫資料分頁載入到RecyclerView裡面。
先給出一個例子，實現一個簡易功能，在Android Room資料庫中增加一批資料，然後在RecyclerView滾動時候，觸發分頁載入邏輯，把資料庫中的資料分頁分段的載入出來，本例中儲存的資料為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 = "輸出";    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 + "重新整理", "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();            }        });        //主動重新整理資料。        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() {            //更新資料的元素個數。            Log.d(TAG + "refreshData", Integer.MAX_VALUE + "");            return Integer.MAX_VALUE;        }        /**         * 在這裡完成耗時的資料載入的耗時任務。         *         * @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("年齡:" + String.valueOf(u.age));            }        }    }    private void writeDatabase() {        Log.d(TAG + "writeDatabase", "開始寫入資料...");        for (int i = 0; i < 100; i++) {            User user = new User();            user.name = "張" + i;            user.age = (int) (Math.random() * 100);            user.updateTime = System.currentTimeMillis();            mUserDao.insertUser(user);        }        Log.d(TAG + "writeDatabase", "寫入資料庫完畢.");    }    @Override    protected void onDestroy() {        super.onDestroy();        mUserDatabase.close();    }}

MainActivity需要的布局檔案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="添加資料" />    <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. */@Daopublic 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();}

代碼運行結果，初始化：




當點擊“添加資料”添加完資料庫資料後，點擊“更新”按鈕後：



小結：
（一）在本例中，使用Android Room獲得分頁資料時候，和之前的UserDao相比，增加了SQL查詢約束LIMIT，關於LIMIT，詳情見附錄文章3。從SQL取資料時，就事先作為分頁，把資料分塊，而不像以前那樣一次性無腦取出資料庫表中的全部資料。從而提高了效能。
（二）AsyncListUtil需要延遲的主動refresh()，才能再初始化後且無滾動RecyclerView時載入出來資料。本例中在MainActivity的onCreate最後，開啟一個線程，該線程故意延遲一定時間，然後才啟動AsyncListUtil的refresh()。之所以這麼做，有部分原因是因為AsyncListUtil和RecyclerView之間，UI繪製和資料的更新沒有同步，導致第一次初始化載入後，無法刷出來資料。明顯的現象就是：如果資料庫中有資料，初次開啟整個程式，RecyclerView載入出來的每個item是空的，但是明明此時資料庫中有資料，按照道理應該初始化載入出來，但是沒有。追蹤代碼就會發現，導致這一現象發生，極大程度上是AsyncListUtil的回調先於RecyclerView完成初始化，導致onDataRefresh和getItemRangeInto
捕捉和使用的第一個和最後一個RecyclerView可見item position均為-1引起。


附錄：
1，《Android官方ORM資料庫Room技術解決方案：@Embedded內嵌對象（二）》連結：http://blog.csdn.net/zhangphil/article/details/78621009 
2，《Android官方ORM資料庫Room技術解決方案簡介（一）》連結：http://blog.csdn.net/zhangphil/article/details/78611632 
3，《SQL資料庫查詢LIMIT 資料分頁》連結：http://blog.csdn.net/zhangphil/article/details/78653677 
4，《基於Android官方AsyncListUtil最佳化改進RecyclerView分頁載入機制（一）》連結：http://blog.csdn.net/zhangphil/article/details/78603499 
5，《基於Android官方AsyncListUtil最佳化經典ListView分頁載入機制（二）》連結：http://blog.csdn.net/zhangphil/article/details/78645089 

Android Room聯合AsyncListUtil實現RecyclerView分頁載入ORM資料