Android Room学习笔记

1，添加KSP插件，在 build.gradle.kts(Project) -> plugins 里添加

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id("com.google.devtools.ksp") version "2.0.21-1.0.28" apply false // KSP 插件

2，添加KSP插件，在 build.gradle.kts(Module) -> plugins 里添加

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id("com.google.devtools.ksp") // 应用 KSP 插件

3, 添加Room依赖，在 build.gradle.kts(Module) -> dependencies 里添加

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implementation ("androidx.room:room-runtime:2.8.4")
implementation ("androidx.room:room-ktx:2.8.4" )// 支持协程
ksp("androidx.room:room-compiler:2.8.4")

4，编写实体类，新建 Banner.kt，写入

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@Entity(tableName = "banner")
data class Banner(
    val desc: String,
    @PrimaryKey
    val id: Int,
    val imagePath: String,
    val isVisible: Int,
    val order: Int,
    val title: String,
    val type: Int,
    val url: String
)

5,编写 BannerDao 文件

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@Dao
interface BannerDao {
    @Query("SELECT * FROM banner")
    suspend fun getBanners(): List<Banner>

    @Query("SELECT * FROM banner WHERE 'id' = :userId")
    suspend fun getBannerById(userId: Int): Banner?

    @Insert(onConflict = OnConflictStrategy.REPLACE) //重复时则会替换。
    suspend fun insert(user: Banner)

    @Delete
    suspend fun delete(user: Banner)

    @Update
    suspend fun update(user: Banner)
}

6,编写 AppDatabase

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@Database(entities = [Banner::class], version = 1)
abstract class AppDatabase: RoomDatabase() {
    abstract fun bannerDao():BannerDao

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

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

7,在 ViewModel 里调用

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class MainViewModel(application: Application) : AndroidViewModel(application) {
    private val _localBanners = MutableStateFlow<List<Banner>>(emptyList())
    val localBanners: StateFlow<List<Banner>> = _localBanners

    fun getLocalBanners() {
        viewModelScope.launch {
            _localBanners.value = AppDatabase.getInstance(application).bannerDao().getBanners()
        }
    }
}