【笔记】Android Room学习笔记

前言

Android Room 学习笔记
使用Room可以简化SQLite数据库的创建和对数据的增删改查

引入依赖

/app/build.gradle

dependencies {

    ...
    
    def room_version = "2.2.0-alpha01"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version" // Room注解处理器
}

创建实体类

• 根据需要操作的数据表结构创建对应的实体类，实体类上使用@Entity注解标注

@PrimaryKey：定义主键
@PrimaryKey(autoGenerate = true)：定义主键自增

/app/src/main/java/.../pojo/User.java

@Entity
public class User {

    @PrimaryKey(autoGenerate = true)
    private Integer _id;
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public Integer get_id() {
        return _id;
    }

    public void set_id(Integer _id) {
        this._id = _id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "_id=" + _id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

创建Dao接口

• 创建Dao接口，定义增删改查抽象方法，可以使用@Query注解手动指定SQL语句

/app/src/main/java/.../dao/UserDao.java

@Dao
public interface UserDao {

    @Insert
    void insertUser(User ... users);

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

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

    @Query("SELECT * FROM user")
    List<User> getAllUsers();

}

创建Database类

• 创建Database抽象类，使用单例模式实例化数据库对象

.allowMainThreadQueries()：强制开启主线程也可以操作数据库，一般在测试时使用

/app/src/main/java/.../UserDatabase.java

// 关联实体类
@Database(entities = {User.class}, version = 1, exportSchema = false)
public abstract class UserDatabase extends RoomDatabase {

    // 将Dao接口暴露给用户
    public abstract UserDao getUserDao();

    // 单例模式
    private static UserDatabase instance;
    public static synchronized UserDatabase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(
                    context.getApplicationContext(),
                    UserDatabase.class,
                    "user_database" // 定义数据库名
            )
                    //.allowMainThreadQueries()
                    .build();
        }
        return instance;
    }

}

自定义数据库引擎类

• 在数据库引擎类中定义增删改查的方法

/app/src/main/java/.../DBEngine.java

public class DBEngine {

    private UserDao userDao;

    public DBEngine(Context context) {
        UserDatabase userDatabase = UserDatabase.getInstance(context);
        userDao = userDatabase.getUserDao();
    }

    /*
    增
     */
    public void insertUsers(User ... users) {
        new InsertAsyncTask(userDao).execute(users);
    }

    static class InsertAsyncTask extends AsyncTask<User, Void, Void> {

        private UserDao userDao;

        public InsertAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(User... users) {
            userDao.insertUsers(users);
            return null;
        }
    }

    /*
    改
     */
    public void updateUsers(User ... users) {
        new InsertAsyncTask(userDao).execute(users);
    }

    static class UpdateAsyncTask extends AsyncTask<User, Void, Void> {

        private UserDao userDao;

        public UpdateAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(User... users) {
            userDao.updateUsers(users);
            return null;
        }
    }

    /*
    删
     */
    public void deleteUsers(User ... users) {
        new InsertAsyncTask(userDao).execute(users);
    }

    static class DeleteAsyncTask extends AsyncTask<User, Void, Void> {

        private UserDao userDao;

        public DeleteAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(User... users) {
            userDao.deleteUsers(users);
            return null;
        }
    }

    /*
    删 全部
     */
    public void deleteAllUsers(User ... users) {
        new InsertAsyncTask(userDao).execute(users);
    }

    static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {

        private UserDao userDao;

        public DeleteAllAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            userDao.deleteAllUsers();
            return null;
        }
    }

    /*
    查 全部
     */
    public void selectAllUsers(User ... users) {
        new InsertAsyncTask(userDao).execute(users);
    }

    static class SelectAllAsyncTask extends AsyncTask<Void, Void, Void> {

        private UserDao userDao;

        public SelectAllAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            List<User> users = userDao.selectAllUsers();
            for (User user : users) {
                user.toString();
            }
            return null;
        }
    }
}

调用引擎类实现增删改查

/app/src/main/java/.../MainActivity.java

public class MainActivity extends AppCompatActivity {

    DBEngine dbEngine;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbEngine = new DBEngine(this);

        // 增 传递新的对象
        User zhangsan = new User("zhangsan", "123456");
        dbEngine.insertUsers(zhangsan);

        // 改 传递新的对象和要修改的id
        zhangsan.set_id(0);
        dbEngine.updateUsers(zhangsan);

        // 删 传递要删除的id
        User user = new User();
        dbEngine.deleteUsers(user);

        // 删除全部
        dbEngine.deleteAllUsers();

        // 查询全部
        dbEngine.selectAllUsers();

    }
}

完成

参考文献

哔哩哔哩——Android架构解析