使用 ROOM 数据库作为单一数据源，配合 LiveData 在 MVVM 模式中实现数据的访问、操作和展示。

示例代码如下：

1. 创建 ENTITY 类

@Entity(tableName = "user") data class User( @PrimaryKey val userId: Long, val userName: String )

2. 创建 DAO 接口

@Dao interface UserDao { @Query("SELECT * FROM user") fun getAll(): LiveData>

@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(user: User)

@Delete
suspend fun delete(user: User)

}

3. 创建数据库单例

@Database(entities = [User::class], version = 1) abstract class AppDatabase : RoomDatabase() { abstract fun userDao(): UserDao

companion object {
    @Volatile
    private var INSTANCE: AppDatabase? = null

    fun getDatabase(context: Context): AppDatabase {
        return INSTANCE ?: synchronized(this) {
            val instance = Room.databaseBuilder(
                context.applicationContext,
                AppDatabase::class.java,
                "app_database"
            ).build()
            INSTANCE = instance
            instance
        }
    }
}

}

4. 在 ViewModel 中使用

class MainViewModel(application: Application) : AndroidViewModel(application) {

private val userDao = AppDatabase.getDatabase(application).userDao()
val users = userDao.getAll()

fun insert(user: User) = viewModelScope.launch {
    userDao.insert(user)
}

fun delete(user: User) = viewModelScope.launch {
    userDao.delete(user)
}

}

5. 最后在 Activity 或 Fragment 中观察 LiveData 并更新 UI

viewModel.users.observe(viewLifecycleOwner, { userList -> // 更新 UI })