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Android 之 Jetpack- Room

news 2025/8/8 5:13:55

以下是一个使用 Kotlin 和 Android Jetpack Room 的完整示例，涵盖 实体定义 → DAO 接口 → 数据库构建 → MVVM 集成 的全流程，采用协程和 Flow 实现异步操作与数据监听。

1. 添加依赖（build.gradle.kts）

dependencies {val roomVersion = "2.7.2"implementation("androidx.room:room-runtime:$roomVersion")kapt("androidx.room:room-compiler:$roomVersion") // Kotlin 注解处理implementation("androidx.room:room-ktx:$roomVersion") // 协程支持implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.8.0") // ViewModel 协程
}

2. 定义实体类（Entity）

@Entity(tableName = "notes")
data class Note(@PrimaryKey(autoGenerate = true) val id: Int = 0,val title: String,val content: String,@ColumnInfo(name = "created_at") val createdAt: Long = System.currentTimeMillis()
)

@Entity：声明数据库表名
@PrimaryKey：自增主键
@ColumnInfo：自定义列名（可选）

3. 定义 DAO 接口

@Dao
interface NoteDao {@Insert(onConflict = OnConflictStrategy.REPLACE)suspend fun insert(note: Note)@Updatesuspend fun update(note: Note)@Deletesuspend fun delete(note: Note)@Query("SELECT * FROM notes ORDER BY createdAt DESC")fun getAllNotes(): Flow<List<Note>> // 使用 Flow 实时监听数据变化@Query("SELECT * FROM notes WHERE title LIKE :query")suspend fun searchNotes(query: String): List<Note>
}

协程支持：所有写操作（Insert/Update/Delete）使用 suspend
Flow 监听：查询返回 Flow，数据变化时自动更新 UI

4. 构建数据库类

@Database(entities = [Note::class], version = 1, exportSchema = false)
abstract class NoteDatabase : RoomDatabase() {abstract fun noteDao(): NoteDaocompanion object {@Volatileprivate var INSTANCE: NoteDatabase? = nullfun getDatabase(context: Context): NoteDatabase {return INSTANCE ?: synchronized(this) {val instance = Room.databaseBuilder(context.applicationContext,NoteDatabase::class.java,"note_database.db").build()INSTANCE = instanceinstance}}}
}

单例模式：避免重复打开数据库连接
@Volatile+ synchronized：确保线程安全

5. 实现 Repository 层（数据抽象）

class NoteRepository(private val noteDao: NoteDao) {val allNotes: Flow<List<Note>> = noteDao.getAllNotes()suspend fun insert(note: Note) = noteDao.insert(note)suspend fun update(note: Note) = noteDao.update(note)suspend fun delete(note: Note) = noteDao.delete(note)suspend fun search(query: String) = noteDao.searchNotes(query)
}

职责分离：ViewModel 不直接操作数据库，通过 Repository 中转

6. 创建 ViewModel

class NoteViewModel(application: Application) : AndroidViewModel(application) {private val repository: NoteRepositoryval allNotes: Flow<List<Note>>init {val dao = NoteDatabase.getDatabase(application).noteDao()repository = NoteRepository(dao)allNotes = repository.allNotes}fun insert(note: Note) = viewModelScope.launch(Dispatchers.IO) {repository.insert(note)}fun delete(note: Note) = viewModelScope.launch(Dispatchers.IO) {repository.delete(note)}
}

协程作用域：viewModelScope自动管理生命周期，避免内存泄漏
后台线程：使用 Dispatchers.IO执行数据库操作

7. 在 Activity 中使用（UI 层）

class MainActivity : AppCompatActivity() {private val viewModel: NoteViewModel by viewModels {NoteViewModelFactory(NoteDatabase.getDatabase(this).noteDao())}override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_main)// 监听数据变化并更新 UIlifecycleScope.launch {repeatOnLifecycle(Lifecycle.State.STARTED) {viewModel.allNotes.collect { notes ->notesAdapter.submitList(notes)}}}// 添加新笔记binding.fabAdd.setOnClickListener {val note = Note(title = "新笔记", content = "内容...")viewModel.insert(note)}}
}// ViewModelFactory（用于依赖注入）
class NoteViewModelFactory(private val dao: NoteDao) : ViewModelProvider.Factory {override fun <T : ViewModel> create(modelClass: Class<T>): T {return NoteViewModel(Application(), NoteRepository(dao)) as T}
}